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Securing the modern Mac: an overview

Modern Macs and macOS feature multiple layers of protection, most of which I have recently described. This article tries to assemble them into an overview to see how they all fit together, and protect your Mac from startup to shutdown. There are also many additional options in macOS and third-party products that can augment security, but I’ll here concentrate on making best use of those that come with a modern Mac and macOS. My recommendations are for the ‘standard’ user, as a starting point. If your needs differ, then you may of course choose to be different, but should always do so in the full knowledge of what you are doing and what its penalties are.

Startup

Whether your Mac has a T2 or Apple silicon chip, it’s designed to boot securely, which means that every stage of the boot process, from its Boot ROM to running the kernel and its extensions, is verified as being as Apple intends. To ensure that, your Mac should run at Full Security. For a T2 model, that means disabling its ability to boot from external disks; for an Apple silicon Mac, that means no third-party kernel extensions. If you need to run your Mac at reduced security, that should be an informed decision when there’s no good alternative.

A vital part of the Secure Boot process is the firmware loaded by the Boot ROM. That needs to be kept up to date by updating to the latest minor release of the major version of macOS. That doesn’t prevent your Mac from staying with an older supported version of macOS, as Apple supplies the same firmware updates for all three supported versions of macOS.

The System volume should be signed and sealed, as the SSV created by a macOS installer or updater. System Integrity Protection (SIP) should also be fully enabled, as without it many macOS security features work differently or not at all. Some need to disable specific SIP features, but again that should only be set when you’re fully aware of their effects and consequences, and should be the minimum needed for the purpose.

User Data

Having got the system up and running, the boot process moves to what is in mutable storage on the Mac’s Data volume. In the internal SSD of a modern Mac, that’s always encrypted, thanks to the Secure Enclave. Although that might appear sufficient, you should always turn FileVault on if your Mac starts up from its internal SSD. That ensures the encryption is protected by your password: an intruder then has to know your password before they can unlock the contents of its Data volume. They have limited attempts to guess that password before the Mac locks them out from making any further attempts. As FileVault comes free from any performance penalty, there’s no good reason for not using it.

Good security is even more important for Data volumes on external boot disks, where FileVault is just as important, but needs additional physical measures to ensure the external disk isn’t mislaid or stolen. That’s a more complex issue, for which the simplest solution is to start your Mac up from its internal SSD with the benefit from FileVault there.

Run Apps

With the user logged in successfully, and the Data volume fully accessible, the next stage to consider is running apps and other software. For this there’s another series of security layers.

When an app is launched or other code run, Gatekeeper will first check it, and in many circumstances run a check for malware using XProtect. Those shouldn’t be disabled, or macOS will still make those checks, but will simply ignore the results. XProtect looks for evidence that the code about to be run matches that of known malware. Although on its own this won’t detect unknown malware, it’s an effective screen against what’s most common. You also need to keep your Mac up to date with the latest security data updates, as those can change every week or two as new malware is identified and included.

Currently, no well-known malware has been notarized by Apple, and most isn’t even signed using a trusted developer certificate. Most therefore attempt to trick you into bypassing checks made by macOS. In Sonoma and earlier, the most common is to show you how to use the Finder’s Open command to bypass the requirement for notarization. As that has changed in Sequoia, those who develop malware have had to adapt, and some now try to trick you into dropping a malicious script into Terminal. Expect these to become more sophisticated and persuasive as more upgrade to Sequoia.

There are simple rules you can apply to avoid getting caught by these. The first time you run any new app supplied outside macOS or the App Store, drag the app to your Applications folder and double-click it in the Finder to open it. If it can’t be launched that way, don’t be tempted to use the Finder’s Open bypass, or (in Sequoia) to enable the app in Privacy & Security settings. Instead, ask its developer why it isn’t correctly notarized. Never use an unconventional method to launch an app: that’s a giveaway that it’s malicious and you shouldn’t go anywhere near it.

macOS now checks the hashes (CDHashes) of apps and code it doesn’t already recognise, for notarization and known malware. Those checks are run over a connection to iCloud that doesn’t need the user to be signed in. Don’t intentionally or inadvertently block those connections, for instance using a software firewall, as they’re in your interest.

Private Data

Traditional Unix permissions weren’t intended to protect your privacy. Now so many of us keep important or valuable secrets in our Home folders, privacy protection is essential. While you might trust an app to check through some files, you may not expect or want that app to be looking up details of your bank cards and accounts.

Privacy protection is centred on a system known as TCC (Transparency, Consent and Control), and its labyrinthine Privacy & Security settings. One of the most tedious but important routine tasks is to check through these every so often to ensure that nothing is getting access to what it shouldn’t.

No matter how conscientious we might be, there’s always the request for access that you don’t have time to read properly, or items that end up getting peculiar consents, like a text editor that has access to your Photos library or your Mac’s camera. Take the time to check through each category and disable those you don’t think are in your best interests. If you get through a lot of new apps, you might need to do this every week or two, but it needn’t be as frequent in normal use, and shouldn’t become an obsession.

There’s some dispute over whether it’s better to leave an app turned off in a category that you control, like Full Disk Access, or to remove it. I tend to disable rather than remove, with the intention of removal later, but seldom get round to that.

Downloaded Apps

While macOS continues checking apps in Gatekeeper and XProtect, there are a couple of other important protections you need to know about. Since macOS Catalina, every 24 hours or so macOS runs a paired set of scans by XProtect Remediator, looking for signs of known malware. If it finds any, it then attempts to remove, or remediate, that. The snag is that it does this in complete silence, so you don’t know whether it has run any scans, and you don’t know if it came across anything nasty, or removed it. I like to know about such things, and have written my own software that lets me find out, in SilentKnight, Skint and XProCheck. One day Apple might follow suit.

Some browsers like Safari have a potentially dangerous setting, in which they will automatically open files they consider to be safe, once they have been downloaded. This can include Zip archives that might not be as innocent as you expect. If you leave that behaviour set, you could discover your Downloads folder with all sorts of items in it. I much prefer to turn that off and handle those downloads myself. You’ll find this control in Safari’s General settings, where it’s called Open “safe” files after downloading.

Bad Links

Most of the protection so far relies more on features in your Mac and macOS, and less on your habits and behaviour. But it’s the user who is the kingpin in both security and privacy protection. Nowhere is this more important than dealing with links in web pages, emails, messages, and elsewhere. If you’re happy to click on a link without checking it carefully, you can so easily end up in the company of your attackers, inviting them into your Mac and all your personal data.

Unless it’s a trusted web page or contact, I always inspect each link before even considering whether to open it. For emails, my general rule is never, and I inspect the text source of each message to see what that really links to. It’s harder on the web, where even ads placed by Google can whisk your browser into an ambush. One invaluable aid here is Link Unshortener, from the App Store, which is a ridiculously cheap and simple way to understand just where those cryptic shortened links will take you. If you can’t convince yourself that a link is safe and wholesome, then don’t whatever you do click on it, just pass on in safety.

Summary

That has been a whirlwind tour through getting the best from macOS security, summarised in the following diagram. Fuller details about each of those topics are easy to find using the 🔎 Search tool at the top right of this page. There’s plenty more to read, and for deeper technical information, try Apple’s Platform Security Guide.

overallsecurity1

Work and play safely!

Is there more XProtection in Sequoia?

If you’ve already upgraded to macOS Sequoia, you’ll probably be well aware of the changes it has brought in updating the data used by XProtect. Although it’s now designed to get those updates from iCloud, so far most have been delivered through the traditional Software Update route, and have had to be installed in their new location either manually in Terminal, or by waiting for the new system to get round to it. So is it worth this extra hassle: how has the new XProtect improved?

We’ve now seen two updates only for Sequoia’s XProtect, one for all Macs, and one only for older macOS. Although still early days, the differences in the XProtect bundle have been obvious. Both versions 5273 and 5275, which were only released for macOS 15, contained large additions to their detection rules, which vanished just as suddenly in 5276, the latest version common to all versions of macOS. To see what has changed, we must examine their XProtect.yara files, the only one in its bundle that has seen any changes.

YARA rules

XProtect performs static checks on code before it’s run, to assess whether there’s evidence that it’s malicious. Its tests are based on YARA rules, explained in detail here. Each rule sets out conditions that must be met for XProtect to conclude that a file is known to be malicious. For example, the rule used by XProtect to detect the Eicar test, a standard non-malicious sample used in testing, is:
rule EICAR
{
meta:
description = "OSX.eicar.com.i"
xprotect_rule = true
condition:
filesize <= 100000000 and hash.sha1(0, filesize) == "3395856ce81f2b7382dee72602f798b642f14140"
}

Its meta section names the detection and states that it’s an XProtect rule. The condition to be met for this rule requires a file size of less than 100 MB and the SHA1 hash of the whole file, from its start (0) to the end (filesize), matches the hash given. Some rules have far more complicated conditions, requiring combinations of tests.

Changing rules

New rules that have only appeared in YARA files used by Sequoia have followed a different pattern. Here’s an excerpt from an example:
rule XProtect_MACOS_DOLLITLE_CT
{
meta:
description = "MACOS.DOLITTLE.CT"
uuid = "[UUID]"
condition:
hash.sha256(0, filesize) == "[SHA256 hash]" or

}

where [UUID] is the rule’s unique identifier, and [SHA256 hash] is the hash value for that part of the condition.

For the first time this rule’s metadata includes a UUID, and its conditions require the SHA256 hash of the file contents to match one of a number of specific values. In this case, the rule gives only six different hashes, but in the rule for MACOS.SOMA.CT there are 3,124 hashes to match against.

So the new YARA rules tested by Apple using Sequoia’s XProtect don’t yet reveal any evidence of new capabilities. What they do suggest is that it’s capable of handling even larger sets of rules, including single rules testing well over 3,000 file hashes. Over the last year, XProtect’s YARA files have increased considerably in their size and complexity. XProtect.yara from version 2173 a year ago had only 223 rules in just over 3,000 lines of code, while version 5275 for XProtect in Sequoia has more than 350 rules requiring nearly 17,000 lines of code.

XProtect future

It seems most unlikely that Apple will ever update Sonoma or earlier versions of macOS to use comparable code in XProtect to that in Sequoia. We have already seen how it has forked XProtect’s YARA rules to deliver different versions for Sequoia and previous macOS, with the newer XProtect receiving odd-numbered releases, and older ones even-numbered. Although those have been confusing for those users who track security data updates, Apple expects us to leave it to macOS to download and install the right updates promptly.

If the last couple of weeks have been chaotic, I fear that the future will be similar. I’ll continue to do my best to inform you of updates to XProtect’s data, and to help you keep your Macs up to date, whichever version of macOS they’re running.

[Thanks to Arnaud for correcting my original reference to file sizes, rather whole-file hashes.]

Living with(out) notarization

When Apple introduced notarization six years ago, it warned us that it would eventually become obligatory for developers, and reassured us that we would still be able to run our own apps that aren’t notarized. macOS Sequoia is the first version of macOS to expect apps delivered from outside the App Store to be notarized, but still to allow us to run apps that aren’t. This article explains how that’s accomplished, and what you should do to work within these new rules.

Sequoia’s rules

When an app is being launched for the first time on that Mac, if it has been put into quarantine with a quarantine extended attribute, Gatekeeper will check whether it has been notarized. If it has, then its launch will progress to further checks such as those of XProtect. If it hasn’t been notarized, then macOS will warn you of that, and halt its launch.

notarizn1

If you want to launch the app despite that warning, open Privacy & Security settings, where you can click the button to Open Anyway.

notarizn2

You will then be warned again, and given the advice “don’t open this unless you are certain it is from a trustworthy source.”

notarizn3

Clicking Open Anyway then takes you to the third dialog, where you’ll need to authenticate to launch the app.

notarizn4

Why all the dialogs?

The old Finder bypass for Gatekeeper was simple: use the contextual menu to Open the app, and there’s a single dialog to get through. That’s so simple that it has become widely used by malware.

zamosshot

These are the helpful instructions provided by one of the most widely encountered malicious apps, Atomic Stealer, when you mount its disk image. The invitation is hard to refuse unless you know the trouble it will bring. Detailing the new bypass system is going to prove a real challenge to those intent on delivering us their malicious apps.

How to run your own apps

The best way to avoid getting embroiled in this process is to build your own apps locally. All modern build systems such as Xcode and its tools now apply an ad-hoc signature to the app or command tool, but their products aren’t put into quarantine. Starting with the source code gives you the opportunity to satisfy yourself that the code hasn’t been tampered with, or is malicious. You may also be able to verify checksums or hashes to provide additional reassurance.

Using pre-built apps and tools brings significant risk. Supply-chain attacks are increasingly common, so even if you’re prepared to trust the source of the app, they may be unaware that it has been tampered with. Remember that, in security terms, there’s no robust way to tell the difference between a benign app and malware unless it has been notarized.

How to move apps between Macs

One of AirDrop’s annoyances is that everything transferred so conveniently also acquires a quarantine extended attribute, so putting it through full Gatekeeper first run checks on notarization. This isn’t just done to annoy, but allows for the fact that AirDropped apps can come from untrusted sources.

If, instead of using AirDrop, you use local file sharing, no quarantine extended attribute is added, and your unnotarized app won’t be put through a full first run check, so you won’t have to suffer the dance of the three dialogs before it will launch.

If you have access to a Developer ID and need to distribute an app more widely, you can notarize other developers’ apps. Apple has made it clear that submission of an app for notarization doesn’t have to be performed by its developer, the owner of the certificate used to sign the app with, but anyone with a current developer account with Apple can do so provided they follow the correct process. This is most appropriate for those in enterprise and organisations who need to use third-party products that aren’t yet notarized by their developer.

Tricks to avoid

You can of course strip the quarantine extended attribute before trying to run an app for the first time. This is a potentially dangerous workaround, as it bypasses first run checks that could spot malware. For those of us who often transfer our own apps for testing using AirDrop, it’s easy to drop them into a folder, Zip that, then on the recipient Mac strip the quarantine xattr before unZipping the archive. My utility Cormorant can make that even simpler. If you were to opt to do that, you must be absolutely certain of the provenance of the app you’re transferring.

For those who have test systems that frequently need to run unnotarized apps, another potential solution has been to disable Gatekeeper on them. Perhaps anticipating a move to do that, Apple has changed how this can be done, making it a two-step procedure, in which you first allow the disabling of checks, then in Privacy & Security settings control how that’s implemented. Apple encourages those who need to do this to use installed profiles instead, or handle it through MDM payloads. This has been explored in detail by Brandon Dalton in his account of these changes.

Is notarization worth it?

In terms of risk alone, only ever running code on your Mac that has been signed by Apple (all macOS code, all App Store apps) or has been notarized by Apple, is almost the safest policy (after running only those apps bundled with macOS). In the early years of notarization, a handful of malicious apps did manage to get notarized for a brief time, but it has been a good while since the last of those. The highest risk strategy is to ignore notarization completely, as it allows all malware to run freely.

There has been a lot of misinformation as to how notarization does or doesn’t work. It’s a key part of Apple’s switch from relying on the chain of trust in code signatures to assessing executable code using its CDHashes. Every notarized app is associated with CDHashes that can verify the integrity of its code, and can be compared against those obtained during the notarization process. This allows Apple to divide code into one of three classes:

  1. known good, gathered from notarization,
  2. known bad, discovered in malicious code in the wild,
  3. unknown, found in code that hasn’t been notarized, or found in known malware.

If all the code that your Mac runs is in the first category, or signed by Apple, then it’s at lowest risk. What you should aim for is to ensure that any code in the third category can’t turn out to be malicious.

Silently updated security data files in Sequoia

Each of the main security services in macOS, such as XProtect, relies on data commonly stored in separate files on the Data volume so they can be updated directly outside full macOS system updates. Those are released silently by Apple, unannounced, and you aren’t even sent a notification when they’ve been updated.

Currently, those most frequently updated are XProtect and XProtect Remediator, normally released in two-week cycles. However, Sequoia has changed the way that XProtect’s data is updated, and it’s now intended occur over a connection to iCloud rather than through Software Update, while XProtect Remediator continues to rely on the latter rather than iCloud.

This article details each of the main security data files found in macOS 15 Sequoia, together with others involved in related system functions. Several other bundles that formerly had roles in security have now been emptied, or left frozen in time, and three have been removed completely; those are listed below for the record. As Apple doesn’t document any of them beyond mentioning their existence and simplified role, the information given is the best that I can find currently.

Main Security Data

XProtectPayloads, alias XProtect.app and XProtect Remediator
Latest version: 145, 3 September 2024.
This contains a suite of specialised malware detection and remediation tools, in the app bundle XProtect.app on the Data volume at /Library/Apple/System/Library/CoreServices. This was introduced in macOS 12.3, then version 62 was pushed to Catalina and later on 17 June 2022. Executables include a replacement for MRT, and many scanners for specific malware types. My free XProCheck inspects its reports for malware detection and remediation. This is normally updated every two weeks using Software Update or a substitute.

XProtectPlistConfigData
Latest version: 1.0 5275, 24 September 2024.
These are the whitelists and blacklists used by XProtect, as detailed here. In Sequoia, two different locations are used: the primary is at /var/protected/xprotect/XProtect.bundle, on the Data volume; the secondary is also on the Data volume at the traditional location of /Library/Apple/System/Library/CoreServices/XProtect.bundle, and is used as a fallback when there’s no bundle at the primary location. While previous versions of macOS still obtain updates through Software Update, Sequoia is intended to update the primary bundle via a CloudKit connection to iCloud, although it can still update the secondary bundle using those released via Software Update when they’re available. This is expected to be updated every two weeks, but may not be the same as updates for previous versions of macOS. You can force an update using the command sudo xprotect update in Terminal, and that will also copy an update obtained through Software Update to the primary location.

Bastion
Latest version: not given, but bundled in the current XProtectPayloads.
These provide rules and exceptions for XProtect Behaviour Service (XBS). First introduced in Ventura, this service monitors for and logs processes that access sensitive locations such as folders containing browser data. As of XProtectPayloads 137 it has 12 Bastion rules, but doesn’t block behaviours, only records them in its database at /var/protected/xprotect/XPdb. Bastion rules are defined in bastion.sb and BastionMeta.plist inside /Library/Apple/System/Library/CoreServices/XProtect.app Those are updated infrequently.

AppleKextExcludeList
Latest version: 20.0.0, 5 September 2024 (15.0 release).
This is a huge list of kernel extensions which are to be treated as exceptions to Sequoia’s security rules, and is stored on the Data volume in /Library/Apple/System/Library/Extensions/AppleKextExcludeList.kext, at Contents/Resources/ExceptionLists.plist.

Others

IncompatibleAppsList
Latest version: 140.191 (15.0 release).
This is a bundle on the Data volume at /Library/Apple/Library/Bundles/IncompatibleAppsList.bundle which contains IncompatibleAppsList.plist, listing many known incompatible versions of third-party products, including Flash Player.

Vestigial Data

MRTConfigData
Latest version: 1.93, 14 July 2022.
This was Apple’s Malware Removal Tool stored on the Data volume at Library/Apple/System/Library/CoreServices/MRT.app, so that it could remove any malware which macOS detected. This has now been replaced by the XProtectRemediatorMRTv3 executable module in XProtect Remediator, and may disappear in future versions of macOS. It usually isn’t installed as part of macOS, but may be later as a security data update.

Gatekeeper Configuration Data (GK Opaque)
Latest version: 181, but can instead be 94.
This is an SQLite database on the Data volume in /private/var/db/gkopaque.bundle/Contents/Resources/gkopaque.db may have been used to provide whitelists for Gatekeeper’s security system, which checks the code signatures of apps. Macs that have never had Catalina or earlier installed normally have the very old version 94, indicating this database is no longer used.

Gatekeeper E Configuration Data (GKE)
Latest version: 8.0.
This is an SQLite database on the Data volume in /private/var/db/gke.bundle/Contents/Resources/gk.db with an additional file gke.auth, which may have provided whitelists for Gatekeeper’s security system. gke.auth is believed to contain data for checking signed disk images, and seems to have remained largely unchanged since Sierra. gk.db was new in Catalina and hasn’t changed since.

Recently Removed

TCC_Compatibility Bundle
This used to be a bundle on the Data volume at /Library/Apple/Library/Bundles/TCC_Compatibility.bundle which has been removed from Sequoia.

Core Services Application Configuration Data
This used to be a bundle on the System volume at /System/Library/CoreServices/CoreTypes.bundle/Contents/Library/AppExceptions.bundle, containing a list of app exceptions in /System/Library/CoreServices/CoreTypes.bundle/Contents/Library/AppExceptions.bundle/Exceptions.plist. This has been removed from Sequoia.

CompatibilityNotificationData
This used to be a bundle on the Data volume at /Library/Apple/Library/Bundles/CompatibilityNotificationData.bundle, containing CompatibilityNotificationData.plist, and listing version ranges of third-party products to be notified as being (in)compatible. This has been removed from Sequoia.

Last updated: 24 September 2024.

Last Week on my Mac: 15.0 or wait for 15.1?

It’s strange to think that, as we’re wondering whether and when to upgrade to Sequoia, Apple’s engineering teams are already at work on macOS 16. While they’re thinking out what we’ll chew over next summer, you may well be asking if you should upgrade to 15.0 next week, wait for the AI features coming in 15.1 next month, or leave your decision until 2025?

For those with Macs and iPhones that can both be upgraded, iPhone Mirroring is probably the most obviously attractive new feature. It completes the integration of Continuity, and could transform your workflows. Fortunately for such a key feature, it should work with all supported Macs, not just Apple silicon models. There’s one small and temporary disappointment, though, as drag and drop between Mac and iPhone isn’t expected in 15.0, but in an update “later this year”.

The new Passwords app should spare you from wanting to pay for a third-party password manager. This is much more than just shelling out the existing Passwords feature from Safari and System Settings, and at last gives full control over passkeys and other shared secrets in your Keychain in iCloud.

Although some see Sequoia’s new dislike for apps that aren’t notarized (or from the App Store) as an unnecessary burden, for most of us this will raise the bar against running malware and increase our margin of safety. It has been some time since any malicious software has been successfully notarized, and most of the current epidemic of stealers aren’t even signed with a Developer certificate. Instead, they usually prompt the user to open them using the existing Finder bypass, something that no longer works in Sequoia without explicitly and individually giving permission to that app in Privacy & Security settings.

It will be interesting to see how malware developers respond to this challenge, as trying to give the user detailed instructions as to how they can be run without being blocked by Gatekeeper should now arouse the suspicion of even the most careless and inattentive.

While we’re on the subject of security, remember that Sequoia is now the only version of macOS that gets full security updates over the coming year. While Sonoma and Ventura will still get some, if you want the lot then you’ll need to upgrade. Monterey, of course, now gets none at all. This gets more brutal when considering other bugs that aren’t relevant to security: those will only be fixed in Sequoia, not even in Sonoma.

For those who virtualise macOS on Apple silicon, support for Apple ID gives VMs access to iCloud Drive at last, although it stops short of enabling the App Store or its apps, so isn’t as useful as it should have been. There are two important restrictions to this:

  • Apple ID can only be used in a Sequoia guest running on a Sequoia host, and
  • the Sequoia VM has to be built from a Sequoia IPSW file, and can’t be upgraded from a Sonoma or earlier VM.

As long as your Mac stays with Sonoma, you won’t be able to use Apple ID in any of its VMs, including Sequoia. This still leaves us with the paradox that Apple wants us to buy and run apps from its App Store, but VMs are the one place where you can’t use them.

Among the less prominent improvements that have caught my attention are a timed messaging feature of Send Later in Messages, and a batch of improvements in Freeform. If you’ve come to like that relatively new app, you should find Sequoia worth the effort. I’ve also been impressed to see one of the oldest bugs remaining in the Finder has finally been addressed in macOS 15. I’ll be putting the bunting out in celebration after I’ve upgraded on Monday.

As with Sonoma, some of the most important new features haven’t been documented even for developers. Among those are changes to XProtect in terms of its updating and management, and speculation as to how that might affect its function. As I have explained, XProtect’s detection rules have grown enormously over the last few months, and it’s likely that Apple intends improving how XProtect can apply its Yara rules, and making their updating more efficient.

Finally, Sequoia is almost certainly going to be delivered as if it were an update, and won’t download its installer app unless you’re upgrading from a significantly older version of macOS, just as has happened in all recent macOS upgrades. Remember that upgrading macOS these days comes with a one-way ticket: changing your mind afterwards will cost you a lot of time and messing about to step back to Sonoma. However, accidental upgrades shouldn’t be feared. For instance, if you inadvertently click the Install all updates button in SilentKnight and want to reverse that for a macOS update, let the download complete, shut down, start up in Safe mode, wait a minute, then restart in normal mode.

Whatever you choose tomorrow, I hope it works well for you. And in case you’re wondering, if you’ve got an Apple silicon Mac, you’re going to love 15.1.

Launching apps in Sonoma 14.6.1: Conclusions

Over a series of three articles last week, I pored over thousands of log entries to examine how macOS Sonoma 14.6.1 checks applications it’s launching, under normal full security settings, with reduced security, and for known malware. This article draws together my conclusions from those tests run in virtual machines on an Apple silicon Mac.

Layered security

Like other security functions in macOS, app launch security is built in layers, including checks of

  • code-signing certificates (multiple times);
  • CDHashes, including their consistency, and against Apple’s database for notarized apps, and their revocation;
  • quarantine extended attributes, which normally trigger a user consent dialog, and may result in app translocation;
  • previous launch, in the LaunchServices database;
  • matches with Yara rules in XProtect’s data;
  • user consent to a first launch prompt dialog;
  • launch and other constraints.

Additional data may also be collected and stored in the provenance database that first appeared in Ventura.

Not all checks are performed on every launch of an app. At a minimum, for a notarized app that has been run only recently, these might consist of only local checks against CDHashes and with the app’s existing entry in the LaunchServices database. Checks are also modified by reducing security settings:

  • Disabling Gatekeeper checks doesn’t stop those checks from taking place, but apparently ignores some results, notably those obtained by XProtect. It doesn’t affect checks of CDHashes against Apple’s database.
  • Disabling SIP has more pervasive effects in largely disabling the com.apple.syspolicy sub-system, affecting several layers, although checks of CDHashes against Apple’s database are unaffected.

com.apple.syspolicy

In full security conditions, one sub-system dominates log entries concerning app launch security, com.apple.syspolicy. This is clearest in Gatekeeper and XProtect checks. Although the log entries that follow may appear bewildering, they are the best illustration of this point.

When launching a notarized app that hasn’t previously been run on that Mac and has a quarantine xattr, Gatekeeper and XProtect scans are reported in the following sequence of entries:
com.apple.syspolicy.exec GK process assessment: <private> <-- (<private>, <private>)
com.apple.syspolicy.exec Gatekeeper assessment rooted at: <private>
com.apple.syspolicy.exec Skipping TCC check due to process: 692, 0, 692
com.apple.syspolicy.exec queueing up scan for code: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: (null)), (id: (null)), (bundle_id: (null))
com.apple.syspolicy.exec starting work for scan for code: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: (null)), (id: (null)), (bundle_id: (null))
com.apple.syspolicy.exec allowUI is YES, creating codeEval object: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: (null)), (id: (null)), (bundle_id: (null))
com.apple.syspolicy.exec Adding default exception for team: <private>
com.apple.syspolicy.exec Registered app bundle for protection: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: QWY4LRW926), (id: (null)), (bundle_id: (null))
com.apple.syspolicy.exec GK performScan: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: QWY4LRW926), (id: (null)), (bundle_id: (null))
com.apple.xprotect XProtectScan beginAnalysisWithResultsHandler continueOnError is set to 0
com.apple.xprotect XPAssessment performAnalysisOnFileImpl continueOnError set to 0
com.apple.xprotect Xprotect is performing a direct malware and dylib scan: <private>

Those checks later complete in entries such as:
com.apple.syspolicy.exec GK Xprotect results: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: QWY4LRW926), (id: (null)), (bundle_id: (null)), XPScan: 0,-7676743164328624005,2024-08-26 08:19:01 +0000,(null)
com.apple.syspolicy.exec GK scan complete: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: QWY4LRW926), (id: (null)), (bundle_id: (null)), 4, 4, 0
com.apple.syspolicy.exec scan finished, waking up any waiters: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: QWY4LRW926), (id: co.eclecticlight.SystHist), (bundle_id: co.eclecticlight.SystHist)
com.apple.syspolicy.exec App gets first launch prompt because responsibility: <private>, <private>
com.apple.syspolicy.exec GK evaluateScanResult: 0, PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: QWY4LRW926), (id: co.eclecticlight.SystHist), (bundle_id: co.eclecticlight.SystHist), 1, 0, 1, 0, 4, 4, 0
com.apple.syspolicy.exec GK eval - was allowed: 1, show prompt: 1
com.apple.syspolicy.exec Skipping TCC check due to process: 692, 0, 692
com.apple.syspolicy Found console users: <private>
com.apple.syspolicy.exec Prompt shown (5, 0), waiting for response: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: QWY4LRW926), (id: co.eclecticlight.SystHist), (bundle_id: co.eclecticlight.SystHist)

When SIP has been disabled, there are precious few entries from com.apple.syspolicy or com.apple.syspolicy.exec. Instead, XProtect appears to be left to its own devices, and doesn’t fare well:
com.apple.xprotect XPAssessment performAnalysisOnFileImpl continueOnError set to 0
com.apple.xprotect XprotectService Calling SecAssessmentCreate with URL <private>, context <private>
XprotectService SecTrustEvaluateIfNecessary
com.apple.xprotect XprotectService Bundle is not apple signed
com.apple.xprotect XprotectService Bundle size result: 18388222 (YES)
com.apple.xprotect XprotectService Always scan: YES
com.apple.xprotect XprotectService Starting malware scan for: <private>
kernel XprotectService [697] crossed memory high watermark (15 MB); EXC_RESOURCE
kernel Full corpse enqueued for XprotectService
com.apple.xnu memorystatus kernel kernel EXC_RESOURCE -> XprotectService[697] exceeded mem limit: ActiveSoft 15 MB (non-fatal)
ReportCrash event condition bump 0 -> 1
ReportCrash post-exception thread qos drop 21 -> 17
ReportCrash PID 697 exceeded the memory high watermark; Invoking ReportMemoryException with corpse.

There are no other entries referring to Gatekeeper or those checks. The effects of disabling SIP appear extensive and pervasive throughout several of the layers of app launch security.

CDHashes are central

With the adoption of notarization, apps run in macOS should now fall into one of five categories:

  • signed by Apple, either its own apps or those delivered through its App Store;
  • notarized by Apple, with its CDHashes added to Apple’s database;
  • signed (either with a Developer certificate, or ad hoc) locally, and not distributed over the internet, with its own unique CDHashes;
  • unwanted or malicious, with revoked CDHashes,
  • unrecognised, and potentially malicious.

These emphasise the importance of the online ‘notarization’ checks of CDHashes performed in all circumstances where macOS doesn’t have previous records of saved CDHashes for that code. Their primary purpose isn’t to validate notarization, but to identify code as known good, known bad, or unknown. When Apple’s security engineers identify new malware, its CDHashes can quickly be added to the database as being revoked, so ensuring that all subsequent checks of the same CDHash will be classified as revoked, for malicious code. This is a rapid response that should have no false positives, in which benign code is mistakenly identified as being malicious.

Typically, the checking sequence is reported in the log with:
com.apple.syspolicy looking up ticket: <private>, 2, 1
com.apple.syspolicy cloudkit record fetch: <private>, <private>
com.apple.syspolicy cloudkit request cache info: <private>, max-age=300
com.apple.syspolicy CKTicketStore network reachability: 1, Mon Aug 26 09:15:45 2024
com.apple.syspolicy Inserting ticket: <private>
com.apple.syspolicy completing lookup: <private>, 0

[and so on with further lookups]
and those are among the only entries from com.apple.syspolicy seen when SIP is disabled.

When full security is enabled, those are completed with
com.apple.syspolicy.exec GK evaluateScanResult: 0, PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: QWY4LRW926), (id: co.eclecticlight.SystHist), (bundle_id: co.eclecticlight.SystHist), 1, 0, 1, 0, 4, 4, 0
But when SIP is disabled, those don’t appear, and seem to be substituted by application of Security rule 11 instead.

The downside of CDHash checks is that their false negative rate can be alarmingly high. Change a single bit in the code being hashed, and the hash will amplify that change, and is completely different. Hence the importance of notarization to establish which CDHashes definitely aren’t from malicious code.

One threat to this system occurs when a user mistakenly blocks their Mac from connecting to Apple’s database using CloudKit, for example using a misconfigured software firewall. Without a suitable vulnerability, malicious software shouldn’t be able to use this approach to block a payload from being checked.

I don’t know whether any third-party security products use a similar checking mechanism with their own local or remote CDHash databases, but this appears to be a great advantage to the protection built into macOS.

Performance

Two of the checks performed with full security enabled are dependent on the size of the app being checked. Fully validating an app’s CDHashes against those in its signature or notarization ticket should benefit from hardware acceleration, particularly on Apple silicon, and can be tackled hierarchically. It appears unlikely to result in significant delays to launching an app.

XProtect scans are more likely to be responsible for observable delays in app launch times, though. With the recent growth in the number of Yara rules, and their length, scans performed after an app’s first launch are the most probable cause of large and complex app bundles requiring several seconds before the app can be run.

Summary

I have updated the flow chart I first proposed as a result of observations made of app launches in Sonoma 14.4.1:

launchsonomaapp2

This is also available as a tear-out PDF here: launchsonomaapp2

I welcome any evidence that will refine and improve that, please.

Previous articles

Launching apps in Sonoma 14.6.1: Full security
Launching apps in Sonoma 14.6.1: Reduced security
Launching apps in Sonoma 14.6.1: Known malware
How does Sonoma check an app before launch? (Sonoma 14.4.1)

Launching apps in Sonoma 14.6.1: Known malware

Previous articles in this series described how macOS 14.6.1 security systems check the launch of apps when full security is in force on an Apple silicon Mac, and how those are changed by disabling SIP and Gatekeeper checks. Those have shown how checks are layered in accordance with the Security architecture of macOS, how different layers are invoked according to the status of an app (whether it’s quarantined, notarized, or has been run previously), and how extensive are the effects of disabling SIP. But no account of app security can be complete without examining how it protects against real malware, the aim of this article.

Methods

In these tests, I have again run four variants of the same 14.6.1 VM:

  • Full Security, with SIP and Gatekeeper/XProtect enabled;
  • Full Security, with Gatekeeper/XProtect disabled;
  • Permissive Security, with SIP disabled;
  • Permissive Security, with both SIP and Gatekeeper/XProtect disabled.

Samples of malicious software were obtained from the Objective-See Foundation’s collection. Three were chosen:

  • Atomic Stealer (AMOS, or Soma)
  • Genieo (InstallMac)
  • XCSSET

These were downloaded directly to each of the four VMs, when they were running in isolation in ViableS. Each was then unZipped and the contents moved to the Documents folder to try to ensure that their code wouldn’t be subjected to app translocation. Full log extracts were obtained from the Full Security VM for the first 5 seconds after launching Atomic Stealer and XCSSET; as the Genieo sample only installed its payload and didn’t launch its code, no log record was obtained for that. Log records weren’t obtained for the other three VMs, although the results of running the malicious payloads were observed for comparison against those of the Full Security VM.

Atomic Stealer

zamosshot

This was presented in a disk image that hadn’t been signed by a Developer certificate, and encouraged the user to try to bypass full Gatekeeper checks by opening the malicious payload CardGame.app using the Open command in the Finder’s contextual menu, a common strategy adopted by malware developers. This ruse was spotted early as a security exception with the code -67062, indicating that the disk image was unsigned, and that resulted in the app being translocated in its disk
SecTranslocateCreateSecureDirectoryForURL: created /private/var/folders/s0/[…]/CardGame.app
This appears to be a less usual cause of translocation, although strictly within its rules.

AMFI quickly found a code signature issue, as reported by the kernel
AMFI: '/private/var/folders/s0/[…]/CardGame.app/Contents/MacOS/My Go Application.app' has no CMS blob?
AMFI: '/private/var/folders/s0/[…]/CardGame.app/Contents/MacOS/My Go Application.app': Unrecoverable CT signature issue, bailing out.
AMFI: code signature validation failed.

Gatekeeper and XProtect scans followed, and the CDHashes were checked with Apple’s database over CloudKit. This discovered that one of the hashes had been revoked
Notarization daemon found revoked hash: {length = 20, bytes = 0xe430ea6d59a70ac00c1b8552092f4de0bbb80232}
resulting in another security exception, this time of -66992, confirming that this code has been revoked. That check was then repeated with the same result.

Shortly after that, the XProtect scan was completed, finding a match for Atomic Stealer A
GK Xprotect results: PST: (vuid: 11F66D42-5827-3465-A741-F434860C2862), (objid: 20), (team: (null)), (id: (null)), (bundle_id: (null)), XPScan: 11,-7676743164328624005,2024-08-27 07:31:10 +0000,MACOS.SOMA.A
and the decision was made to present the malware warning prompt
present prompt: uid=501, conn=yes, type=Malware, op.ident=2F90B5EF-D483-43C7-BBD1-77E8EABF4D62, info.ident=8D56578B-833F-4629-86F0-4E0A8EDD7D49, info={<private>}
indicating that it’s game over for the CardGame app and its disk image.

This sample of Atomic Stealer was thus detected by two different and independent methods: its CDHash ‘notarization’ check revealing its revocation, and the XProtect scan matching it to the known signature of MACOS.SOMA.A. As the first of those is unaffected by disabling SIP or Gatekeeper, it’s not surprising that the sample was detected and blocked in each of the four VMs.

Genieo

zgenieshot

This was presented in an Installer package as an Intel binary. This claimed to install “Apple software” and triggered a request to download and install Rosetta 2 if that wasn’t already available. The installer appeared to complete without eliciting any warnings, and it’s presumed that the malware would either have been detected later when there was an attempt to launch it, or in an XProtect Remediator scan.

All four VMs behaved identically, and there was no sign of recognition that the software installed might be malicious. This raises questions about the security inherent to Installer packages and whether there might be exploits available using Intel binaries in Rosetta 2, given that it resigns translated executable code.

XCSSET

zxcsshot

This was presented in a bogus app named Xcode. Attempting to run that resulted in its detection, and the invitation to remove it, in this case without it being positively identified.

As this was presented as an app containing unsigned code, that came under suspicion early during its assessment, and it was translocated even though it had been moved from its original location
SecTranslocateCreateSecureDirectoryForURL: created /private/var/folders/s0/[…]/Xcode.app
That appears to have occurred beyond previous rules for translocation.

Gatekeeper and XProtect scans followed, and it was confirmed that the code was unsigned
Error Domain=NSOSStatusErrorDomain Code=-67062
Unsigned code in: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 81906), (team: (null)), (id: (null)), (bundle_id: (null))

CDHash checks using CloudKit didn’t find a match, and were simply reported as
ticket not available: <private>
Gatekeeper’s scan reported that the app didn’t contain a bundle, but XProtect found no match with current Yara rules. The decision was made to present the malware warning prompt
present prompt: uid=501, conn=yes, type=Malware, op.ident=A66F9ED6-EDE7-48E9-B1F8-74CB77C43C9E, info.ident=39D1FBB5-2620-483B-AD3C-6FC5118A406F, info={<private>}
and the attempt to launch the app was blocked.

As these traits would still be detected with SIP and Gatekeeper disabled, all four VMs blocked the code and displayed the same alert to the user.

Limitations

In reality, it’s common for attacks to consist of the initial download of a small dropper, which in turn downloads the main payload. One of the disadvantages of testing malware samples is that this presentation of the payload can’t be taken into account. Payloads are often downloaded using methods that escape quarantine. Another significant difference is that samples often lack code signatures that may be present in the originals, and may change frequently as Developer certificates are revoked and replaced.

Detection information

There appears to be almost no information on how macOS detects different groups of malicious software. Inevitably, Apple provides none at all, and few in-depth analyses of malware give any details about its presentation, in terms of any signatures used, and whether they or CDHashes have since been revoked by Apple. This is a difficult area, given that many of those who analyse and report on malware work for vendors of security products. There appears to be a valuable role for independent assessment of whether and how detection takes place in macOS, major factors in any risk assessment.

I’d like to express my gratitude to the Objective-See Foundation for collecting and making available its extensive library of malware samples, without which none of these tests would have been possible.

Launching apps in Sonoma 14.6.1: Reduced security

In the first of these articles, I examined security aspects of the process of launching various app configurations in macOS Sonoma 14.6.1, on an Apple silicon Mac with full boot security and other security settings. This article moves on to discover how those change when boot security and security settings are reduced. Full details of how this was done are given in the previous article.

To remind you, the apps used were:

  • SystHist – notarized, quarantined, moved from its landing folder to avoid app translocation;
  • SilentKnight – notarized, not quarantined, previously run;
  • Sparsity – notarized, not quarantined, not previously run;
  • DelightEd3 – not notarized, signed with a Developer certificate, not quarantined, not previously run;
  • DelightEd3resigned – not notarized, ad hoc signed, not quarantined, not previously run.

None of the apps run in an app sandbox, and those notarized use a hardened runtime.

This article covers these three variants of the same 14.6.1 VM:

  • Full Security, with Gatekeeper/XProtect disabled;
  • Permissive Security, with SIP disabled;
  • Permissive Security, with both SIP and Gatekeeper/XProtect disabled.

In each VM, settings were confirmed using SilentKnight, which in turn calls standard system tools to determine current security settings, such as those when both SIP and Gatekeeper were disabled.

sksipoff

Gatekeeper disabled

Surprisingly, with Gatekeeper assessments disabled, com.apple.syspolicy.exec still reported that Gatekeeper assessments were made
GK process assessment: <private> <-- (<private>, <private>)
Gatekeeper assessment rooted at: <private>

and later
queueing up scan for code: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 69229), (team: (null)), (id: (null)), (bundle_id: (null))
GK performScan: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 69229), (team: QWY4LRW926), (id: (null)), (bundle_id: (null))

Following that, XProtect scanned
XPAssessment performAnalysisOnFileImpl continueOnError set to 0
Xprotect is performing a direct malware and dylib scan: <private>

using its standard Yara rules.

CloudKit ticket lookup also proceeded as normal. After a while, though, XProtect announced
Xprotect is skipping executable assessment: <private>

This concluded with
GK scan complete: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 69229), (team: QWY4LRW926), (id: (null)), (bundle_id: (null)), 4, 4, 0
and
GK evaluateScanResult: 0, PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 69229), (team: QWY4LRW926), (id: co.eclecticlight.SystHist), (bundle_id: co.eclecticlight.SystHist), 1, 0, 1, 0, 4, 4, 0
GK eval - was allowed: 1, show prompt: 1

The normal prompt for user consent was displayed, and handled as expected. Following that, launch proceeded normally.

Similar entries appeared in the checks made on all apps that had undergone Gatekeeper and XProtect assessment when full security was in force. There is nothing in the log entries to indicate that disabling Gatekeeper had any effect on the checks that were made, although as none of these apps failed assessment, it’s possible that any failures would have been ignored.

SIP disabled

When SIP was disabled, the structure of pre-launch assessments changed, and appeared disordered in comparison to those performed under full security and with only Gatekeeper disabled. Most notable, perhaps, was the almost complete absence of log entries from the com.apple.syspolicy subsystem, which in full security is so prominent, although its service syspolicyd did appear in entries.

Although quarantine was recognised, no entry reported the start or conclusion of any GK (Gatekeeper) assessment, nor subsequent XProtect scans. Instead, the XProtect service wrote
Bundle is not apple signed
Bundle size result: 18388222 (YES)
Always scan: YES

Normal ticket checks were made via CloudKit, but shortly after those were completed, XProtect tried to use its standard Yara rules, and ran out of memory doing so, with the kernel reporting
process XprotectService [697] crossed memory high watermark (15 MB); EXC_RESOURCE
XProtectService therefore ran into trouble before it had even started to scan the app. While some entries suggested prompting the user for their consent, that doesn’t appear to have happened. Eventually the app launched in spite of the disorder that had preceded.

When launching a notarized app that wasn’t quarantined, neither Gatekeeper nor XProtect appear to have had any involvement in the approval of the launch.

SIP and Gatekeeper disabled

Results were essentially identical to those obtained with SIP alone disabled, even down to XProtectService exceeding its memory high watermark, and the almost complete absence of log entries from the com.apple.syspolicy subsystem.

SIP and Gatekeeper settings

Prior to examining these log records, I thought I had a clear idea as to what these two controls do. In fact, neither of them does what you’d expect.

Disabling Gatekeeper or XProtect checks doesn’t stop them from occurring, although it might result in macOS ignoring any errors they might find. That would be consistent with the statement in the spctl man page: “Operations that would be denied by system policy will be allowed to proceed; assessment APIs always report success.”

On the other hand, disabling SIP almost completely stops the whole com.apple.syspolicy subsystem, which ordinarily plays a major role in pre-launch checking of apps. This effectively kills both Gatekeeper and XProtect, leaving those checks in disarray. When the XProtectService tries to lend a hand, its attempt to ingest the current Yara rules runs it out of memory, and it appears unable to render any useful assistance to the pre-launch checks.

This may explain why disabling SIP has the effect of shortening the time to launch an app, most noticeably with larger and more complex apps. In return for launching in a shorter time, the app probably isn’t checked against XProtect’s Yara definitions, so could still contain malicious code that would pass undetected.

In the next article I’ll show what does happen when this system encounters live malware.

Launching apps in Sonoma 14.6.1: Full security

This is the first of a series of three articles that look in detail at the launch process of apps in macOS Sonoma 14.6.1, with the emphasis on security checks. This follows my earlier look in 14.4.1, and covers a wider range of situations, including the effects of disabling SIP and Gatekeeper, and how known malicious software is handled.

Methods

All tests were performed in a series of Sonoma 14.6.1 virtual machines (VMs) running on a Mac Studio M1 Max host, also running 14.6.1. VMs are preferred as they enable a consistent environment and easy control of boot security and security settings, together with relatively low rates of log entries. Log extracts were obtained using Ulbow and analysed in their entirety for the first 5-7 seconds after launching apps in the Finder.

Apps used were:

  • SystHist – notarized, quarantined, moved from its landing folder to avoid app translocation;
  • SilentKnight – notarized, not quarantined, previously run;
  • Sparsity – notarized, not quarantined, not previously run;
  • DelightEd3 – not notarized, signed with a Developer certificate, not quarantined, not previously run;
  • DelightEd3resigned – not notarized, ad hoc signed, not quarantined, not previously run.

None of the apps run in an app sandbox, and those notarized use a hardened runtime.

Four variants of the same 14.6.1 VM were run:

  • Full Security, with SIP and Gatekeeper/XProtect enabled;
  • Full Security, with Gatekeeper/XProtect disabled;
  • Permissive Security, with SIP disabled;
  • Permissive Security, with both SIP and Gatekeeper/XProtect disabled.

All had bridged network access to the network and internet, and shared folders with the host, when running these non-malicious apps.

This article describes what happens in the log in the first of those conditions, full security with both SIP and Gatekeeper/XProtect enabled.

Quarantined notarized app

This underwent the fullest checks of these tests. Once LaunchServices announces that it’s opening the app, the following sequence of events is recorded.

CDHashes from the app are copied, here only those for the Arm architecture. As the app is unknown, it’s next registered with LaunchServices. Gatekeeper assessment is then started just 0.07 seconds after announcement of the launch, in the log entry
GK process assessment: <private> <-- (<private>, <private>)
com.apple.syspolicy.exec then starts work on scanning for code, followed by the first mention by LaunchServices that the app is quarantined.

The Gatekeeper scan is announced in
GK performScan: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: QWY4LRW926), (id: (null)), (bundle_id: (null))
followed by the XProtect scan in
Xprotect is performing a direct malware and dylib scan: <private>
and assignment of the risk category according to its quarantine
QUARANTINE: Setting risk category to LSRiskCategoryUnsafeExecutable
XProtect states the Yara rules it’s using
Using XProtect rules location: /Library/Apple/System/Library/CoreServices/XProtect.bundle/Contents/Resources/XProtect.yara

com.apple.syspolicy next processes the app’s notarization ticket
looking up ticket: <private>, 2, 1
by trying to fetch its record using CloudKit. That’s followed by entries indicating the network access required to connect with iCloud and check the ticket. Success is reported by com.apple.syspolicy in
CKTicketStore network reachability: 1, Mon Aug 26 09:15:45 2024
looking up ticket: <private>, 2, 0

and further lookups.

A little later, Gatekeeper announces the XProtect results
GK Xprotect results: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: QWY4LRW926), (id: (null)), (bundle_id: (null)), XPScan: 0,-7676743164328624005,2024-08-26 08:19:01 +0000,(null)
and its scan is complete
GK scan complete: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: QWY4LRW926), (id: (null)), (bundle_id: (null)), 4, 4, 0

Because this is the first launch of a quarantined app, com.apple.syspolicy.exec decides it gets a first launch or “code-evaluation” prompt “because responsibility”. If the user gives approval, the app is allowed to proceed. Its quarantine flag is updated, and the bundle record registered as trusted. The final step is then to create and save its provenance data
Created provenance data for target: TA(e8217440d9326f59, 2), PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: QWY4LRW926), (id: co.eclecticlight.SystHist), (bundle_id: co.eclecticlight.SystHist)
Handling provenance root: TA(e8217440d9326f59, 2)
Wrote provenance data on target: TA(e8217440d9326f59, 2), PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 62947), (team: QWY4LRW926), (id: co.eclecticlight.SystHist), (bundle_id: co.eclecticlight.SystHist)
Putting executable into provenance with metadata: TA(e8217440d9326f59, 2)
Putting process into provenance tracking with metadata: 692, TA(e8217440d9326f59, 2)
Tracking process with attributes: 692, TA(e8217440d9326f59, 2)

Without quarantine

A notarized app that hasn’t been run previously on that system and isn’t quarantined undergoes a similar sequence, but without the first launch or “code-evaluation” prompt. Its bundle record is registered as trusted, rather than being classified as an Unsafe Executable, but it still gets a full XProtect scan and ticket lookup using CloudKit.

Subsequent launches

The briefest launch process is that for an app that has only recently been run. That appears to skip Gatekeeper and XProtect assessments, and there’s no ticket lookup either. Pre-launch processes can then take less than 0.1 second.

Launching a known app following a cold boot can be as quick, although in this case there is a brief Gatekeeper assessment reported in the log. The key entry here comes from com.apple.syspolicy.exec:
Code already evaluated, using results.
Those are checked by Gatekeeper before launch proceeds, with the kernel reporting
evaluation result: 2, exec, allowed, cache, 1724654056, 4, c0a2e35c20a69dfd, /Applications/SilentKnight.app

Signed with developer certificate

An unquarantined app that isn’t notarized but is correctly signed using a Developer certificate is similar to its notarized equivalent, except that looking up the ticket using CloudKit is of course unsuccessful. Repeated attempts are made to find it, though, before going on to check “the legacy list” and check “legacy policy”. This results in the decision
Match downgraded from DevID to None based on legacy policy for: PST: (vuid: 7C5C43BF-A338-4228-B61E-5038F1D93EDB), (objid: 60118), (team: QWY4LRW926), (id: (null)), (bundle_id: (null))
but the kernel decides to allow launch to proceed
evaluation result: 6, exec, allowed, cache, 1724660700, 0, 9576bac3e248c07b, /Applications/DelightEd3.app

Ad hoc signature

This is detected early during pre-launch checks by AMFI (Apple Mobile File Integrity), despite the bundle record being registered as trusted. The kernel reports
AMFI: '/Applications/DelightEd3resigned.app/Contents/MacOS/DelightEd' is adhoc signed.
AMFI then records
No certificate chain found
Failure getting cert chain
Basic requirement validation failed, error: Error Domain=NSOSStatusErrorDomain Code=-67050 UserInfo={SecCSArchitecture=<private>}

and an error code of -423, given as “The file is adhoc signed or signed by an unknown certificate chain”.

Despite that, Gatekeeper assessment continues, with an XProtect scan. Attempts to look up the app’s ticket inevitably fail despite many attempts, and an error code of -67018 “Code did not match any currently allowed policy” is awarded. Launch then proceeds.

In the next article I’ll show how those are affected by disabling SIP and Gatekeeper assessments.

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