Loose words confuse, and one of the words used most loosely in macOS is permissions. This explainer tries to separate them from other access controls.

Permissions

The access permissions of files and folders are set in their attributes in the file system, stay with that item, and are applied universally for all apps and processes that try to access them.

The simplest and most basic of access controls, these can be inspected and changed in the Finder’s Get Info dialog for all accessible files and folders. They control the ability of apps and other code to read from and write to each file and folder. Normally, if you’re the named owner of a file or folder, you expect to have both read and write access, and that ensures the apps you run with user privileges can open, edit and save changed files.

Permissions are relatively crude controls, so Access Control Lists (ACLs) can refine those permissions with more specific restrictions. They were introduced in Mac OS X 10.4 Tiger in 2005, and are now applied as standard to some widely used folders including the Home folder. The presence of ACLs is normally indicated in the Get Info dialog by the words You have custom access.

No matter what security controls and privacy protection might give you access to, they can’t override the fundamental limits imposed by permissions, and can only limit access further.

Security controls

The macOS security system imposes its own controls according to its rules. Most obvious among those are System Integrity Protection (SIP) and sandboxing.

SIP was introduced in 2015 with El Capitan, and primarily puts system folders, files and some components, including certain extended attributes, beyond the reach of even the root user. The only way to get past SIP is to disable it, a serious undertaking as it has more general effects on security.

Sandboxing is security protection that limits the files individual apps can access by imposing a sandbox as set by their entitlements. It’s therefore determined by the app trying to access files, and doesn’t apply to apps that don’t run in the sandbox. As an app’s entitlements are baked into its signature, there’s nothing a user can do to alter them.

Privacy protection

macOS designates certain locations and resources as being private, and protects them using its Transparency, Consent and Control (TCC) system. Although it has a longer history, this was first implemented in its current form in macOS 10.14 Mojave in 2018, and since then has grown with every new major version of macOS. Privacy protection operates outside of file attributes, using a rule-based system applied to each app, and applies to command tools and other processes as well.

Among the folders this protects are the Desktop, Documents, Downloads, and those on removable storage. While access to individual folders is controlled, if you do encounter problems it’s usually simplest to add that app to the list of those with Full Disk Access, in Privacy & Security settings, in the first instance. That can leave a lot of apps with unnecessary access to private data, so you should periodically check through the list of apps with Full Disk Access to ensure they all still require it. Remember that Full Disk Access can’t override restrictions imposed by permissions or ACLs.

In Tahoe, privacy-protected folders include:

• ~/Desktop
• ~/Documents
• ~/Downloads
• iCloud Drive
• third-party cloud storage
• removable volumes
• network volumes
• Time Machine backups.

Unlike permissions and security controls, there’s no command line interface to these controls, which can only be accessed by the user in Privacy & Security settings. As a result, TCC uses an attribution chain that traces up through the call chain to an app that is responsible for the privacy settings to be applied. For example, when you run commands in Terminal, the privacy settings used by TCC are those of the Terminal app, while helper apps are normally the responsibility of their parent app.

Privacy protection is built around the user’s consent and intent. When a process tries to save a file to a protected folder that it doesn’t already have access to, you should be prompted to give your consent before TCC allows that. Alternatively, when an app tries that, it should display the File Save dialog, where you can express your intent to save the file to that folder. Without consent or intent, TCC should block that file from being saved there unless that app has been given Full Disk Access in Privacy & Security settings.

Privacy protection is the most complex and opaque of these, and can present the toughest problems to solve.

Key points

• Permissions by attributes
• Security by security system
• Privacy protection by TCC, the app and rules
• Loose words confuse.

Some who use SilentKnight for the first time discover that their Mac has been running for months with one of its security systems disabled. As macOS doesn’t have a dashboard to warn you of such dangerous settings, you may not notice until it’s too late. This article explains how to check those essential security settings on Macs with T2 or Apple silicon chips, and how to put them right. Intel Macs without T2 chips are different, and are covered in a previous version.

Secure Boot

Running your Mac in Full Security ensures it gets full protection from its Secure Boot technology. In an Apple silicon Mac this prevents it from loading third-party kernel extensions, and requires recent approved versions of macOS. Check this in System Information by selecting the Controller item in its Hardware section, or in SilentKnight.

This is controlled in Startup Security Utility, accessed from Recovery. Note that it only works with the paired Recovery system, the one you normally use; Apple silicon fallback Recovery doesn’t have this ability.

If you need to run kernel extensions or other software that can’t be loaded in Full Security, use Startup Security Utility to set the Mac to Reduced Security, and enable kexts. Avoid doing this if at all possible.

Settings are different for Intel Macs with T2 chips, where there are three levels of boot security, and the most common reason for reduction from Full Security is to enable that Mac to boot from external drives, something that Apple silicon Macs can do in Full Security.

System Integrity Protection (SIP)

Since El Capitan, macOS has protected all its system files, even down to bundled apps, using System Integrity Protection. This should make it impossible for malware or other software to change those protected files. SIP is also required for a wide range of other security protection, and should be fully enabled unless you have a compelling reason for disabling it partially or completely. In Apple silicon Macs, its status is reported in System Information’s Controller item, but Intel Macs instead give it in the Software section. It’s also checked by SilentKnight and Skint.

You can turn SIP off, something very occasionally needed to perform certain essential tasks. Doing so requires you to start up in Recovery mode, enter a command in Terminal there, and restart; Apple silicon Macs also need to have their boot security reduced in Startup Security Utility before SIP can be disabled.

To enable SIP, start up in Recovery mode, open Terminal, and type the following command:
csrutil enable; reboot
Once that’s done your Mac will restart in normal mode, and you should confirm that SIP is reported as enabled.

If you ever do need to disable SIP, do yourself a favour and put a sticky note on your Mac’s display to remind you to turn it back on.

Gatekeeper/XProtect

Gatekeeper runs checks on apps when they’re opened, and those can include scans for known malicious software using XProtect. As part of your Mac’s frontline protection against malware, you should leave those enabled unless there’s a compelling reason to temporarily disable them. However, I don’t know of anywhere in the macOS GUI that informs you whether these checks are being performed, although they are reported by SilentKnight and Skint.

If it has been disabled, you may be able to enable it using the command
spctl --enable
but chances are that you will instead need to invoke
sudo spctl --global-enable
requiring you to authenticate using your admin password. Be careful with those commands: the hyphens before enable and global-enable aren’t long dashes, but two separate hyphens.

Signed System Volume (SSV)

When you install Big Sur or later, the vast majority of its system files are saved in its System volume. For your Mac to boot from this, it has to be turned into a snapshot, sealed using a tree of cryptographic hashes, and the master seal ‘signed’ by a hash, which is compared against that set by Apple. This signed system volume is extremely secure and thoroughly reliable. On Intel Macs, this is only reported in Disk Utility, but Apple silicon Macs list it in System Information as well. It’s also reported by SilentKnight and Skint.

The SSV should always be enabled. If it isn’t, you’ll need to re-install macOS.

FileVault

Intel Macs with T2 chips and Apple silicon Macs encrypt the whole of the Data volume on their internal SSD. By default, that uses an internally-generated key that’s used automatically when any user logs in. Although it provides good security in most situations, you’re far better off enabling FileVault, as that protects the encryption key with your password as well. This imposes no overhead on accessing encrypted data, and provides valuable protection for your data at no cost.

Check whether FileVault is enabled in Privacy & Security settings, where you can enable it if it’s not already turned on. SilentKnight checks it as well.

macOS and firmware

To ensure your Mac and its apps are best protected from malware, keep its firmware and macOS up to date. As those are updated together, Macs with T2 or Apple silicon chips that are running the most recent release of their major version of macOS will also be running the current firmware, which no longer needs to be checked separately. Check the version of macOS in the About This Mac command at the top of the Apple menu.

Apple lists current supported versions of macOS on its Security Releases page. Those, and versions of security data software, are also listed and detailed here on this page.

If your Mac is running an older release of macOS and its firmware, update them together using Software Update in General settings.

XProtect Remediator scans

This anti-malware scanner performs automatic background scans to detect and remove a wide range of malicious software. It’s normally scheduled to run at least once a day, when your Mac is awake but not busy, and supplied with mains power. You’re wise to check that its scans are being run correctly, and will probably want to know if it has detected and remediated any malware. SilentKnight and Skint run a quick check of its activity over the previous 36 hours, and XProCheck provides detailed reporting and analysis.

Over the last year or so, XProtect Remediator has been using a timer during its scans, and automatically cancelling them if a scan takes longer than allowed. On many Macs, most scans are terminated early, and that results in warnings from SilentKnight and Skint. If you’re concerned, check the reports in XProCheck, where you’ll see that plugin was cancelled with a status_code of 30, as is typical with the timer.

Check:

• the Mac boots in Full Security, if possible,
• SIP is enabled,
• Gatekeeper/XProtect is enabled,
• it has booted from an SSV,
• FileVault is enabled,
• it’s up to date with macOS,
• XProtect Remediator scans are taking place daily.

SilentKnight does all of those and more.