XProtect is the front-line tool in macOS for detecting known malware. When a downloaded app is run for the first time and put through Gatekeeper checks, those rely on detection rules defined in the XProtect.yara file inside the XProtect bundle in /System/Library/CoreServices. Those are updated periodically to extend their coverage as new malware is detected and analysed by Apple’s security engineers. This article looks at how they have changed over the last six years.

My starting point is XProtect version 2103 released on 2 May 2019, in the heyday of macOS 10.14.4 Mojave. That contains a total of 92 rules in a text file of 42,903 bytes, for an average rule size of 456 bytes. Among those are many old chestnuts such as Bundlore.

My end point is version 5310 released this week, on 12 August 2025, for macOS 15.6 Sequoia and earlier. That contains a total of 372 rules in a text file of 969,662 bytes, giving an average rule size of 2,572 bytes. Still among those are the same old chestnuts including Bundlore.

Thus the number of rules is now 4 times what it was six years ago, and they take over 22 times as much space.

For the period up to the end of 2023, I have analysed XProtect’s Yara file in updates every 6 months, in May and November, or the closest update available. From the start of 2024 updates became more frequent, and I have therefore analysed the last update in each month. In late 2024, XProtect in macOS Sequoia started using iCloud to deliver its XProtect data updates. For this analysis I have excluded version 5273, which was only released via iCloud and wasn’t provided through the regular softwareupdate route used by all previous versions.

The number of Yara rules increased steadily until updates became more frequent in 2024, following which there was a very steep rise early that year. Since then they have continued to rise more steeply than before 2024, but now appear more linear, as seen in the red line of regression. Over this period, hardly any Yara rules have been removed.

Total size of the Yara file has followed a similar pattern, with little change until the start of 2024. It then peaked briefly before reducing slightly, pausing a little, then undergoing a step increase from 288 KB to 877 KB. Growth has been steadier for the last year, although it appears to be on track to reach 1 MB in 2026.

Average size of Yara rules changed little between 2021-2023, but increased greatly with the addition of some very large rules in June-July 2024. It has since declined slowly, as more recent rules have been far smaller.

This prodigious growth in the number of Yara rules and their size has inevitably had its effect on the time taken to complete Gatekeeper checks that include XProtect scans. macOS Tahoe has been promised to limit that, by not scanning notarized apps with XProtect, so improving app launch times.

Given that remarkably few old Yara rules have been removed over the last six years, this growth has been inevitable. However, unless old malware is incapable of being run on Macs still supported by XProtect updates, it’s hard to see how it could be safe to remove old rules. When support for running x86 code (except that for “older unmaintained gaming titles”) is dropped from macOS 28, many older Yara rules could be dropped from XProtect updates without putting Apple silicon Macs at risk, but even that isn’t an easy decision. In the meantime, at least our faster Macs should be able to complete XProtect scans more quickly.

Apple has just released updates to XProtect for all supported versions of macOS, bringing it to version 5309, and to XProtect Remediator for all macOS from Catalina onwards, to version 153. As usual, Apple doesn’t release information about what security issues these updates might add or change.

Yara definitions in this version of XProtect add a single new detection rule for MACOS.SOMA.JUENB, part of the Soma/Amos family.

XProtect Remediator doesn’t change the list of scanner modules.

There are extensive changes to the Bastion rules, which add a new definition for common system binaries, extend Rule 1 coverage to include support folders for more browsers, tweak Rules 3 and 14-17, and add new Rules 18-24.

You can check whether these updates have been installed by opening System Information via About This Mac, and selecting the Installations item under Software.

A full listing of security data file versions is given by SilentKnight and SystHist for El Capitan to Tahoe available from their product page. If your Mac hasn’t yet installed this update, you can force it using SilentKnight or at the command line.

If you want to install these as named updates in SilentKnight, their labels are XProtectPayloads_10_15-153 and XProtectPlistConfigData_10_15-5309.

Sequoia and Tahoe systems only

The XProtect update has already been released for Sequoia and Tahoe via iCloud. If you want to check it manually, use the Terminal command
sudo xprotect check
then enter your admin password. If that returns version 5304 but your Mac still reports an older version is installed, you may be able to force the update using
sudo xprotect update

This week’s security data updates were quite a surprise. We’ve grown accustomed to Apple tweaking XProtect’s data most weeks, but this week was a bit different, and came with an update to XProtect Remediator as well, the first in four months. This article explores what they have brought.

Although this security data all goes under the name of XProtect, there are three different protection systems involved.

The traditional XProtect contains a set of ‘Yara’ rules used when performing Gatekeeper scans of new executable code, most notably when a quarantined app is first run, although recent macOS also runs XProtect checks on other occasions. Those rules are used to determine whether the code being scanned is known to be malicious, and if it’s found to be positive, macOS refuses to run that code and you’re told to trash the app.

XProtect Remediator only runs in Catalina and later, where it performs daily background scans to detect and remove software it believes to be malicious. It currently contains 24 separate scanning modules, each designed to detect and ‘remediate’ a different family of malware. Some of its modules also use the detection rules in traditional XProtect, so are improved by regular XProtect data updates. Surprisingly, if XProtect Remediator detects and removes malware, you aren’t notified, although that is recorded in the log and reported as an Endpoint Security event that can be detected by some third-party security software.

Inside the XProtect Remediator app are two files used by the third XProtect, which detects potentially malicious activity such as tampering with parts of a browser’s files. This is therefore referred to as XProtect Behavioural, or by the name it gives to the detection rules it uses, Bastion. Unlike the other two XProtects, this doesn’t rely on performing static checks, but is watching constantly for malicious activity. Although it records that in its local database, at present it doesn’t inform the user, but reports the activity to Apple, to help it acquire intelligence to improve the battle against malware.

XProtect

XProtect version 5304, provided by Apple on 8 July, makes substantial changes to its Yara detection rules to add what appears to be a new family of malware, code-named Bonzai. New rules refer to five different forms, which are most likely to be different components in the same malware, or separate variants, named Bonanza, Barricade, Blaster, Bonder and Banana. It’s likely that independent security researchers will identify these in the coming days, but for the moment the public name of this malware isn’t known.

Looking through these new Yara rules, they look most likely to be for a ‘stealer’, a type of malware that’s currently prevalent, and steals your secrets to send them to a remote server. There are references to Chrome, Brave, Edge and Firefox extensions, and most interestingly some of the malware has been compiled from code written in the Go language, which is becoming popular in cross-platform malicious code.

The last times that Apple added detection rules as substantial as these were in XProtect version 5284 for Adload and Bundlore, and in 5269 for Dolittle, each being major threats.

Bastion

Until now, the behavioural rules used by Bastion have evolved steadily, and the most rules added in one release has only been two, when XProtect Remediator version 123 came with rules 8 and 9, and changes to rule 7, back in January 2023. This update brings four new rules:

• Rule 14 detects sending AppleEvents to Safari, Firefox or Chrome.
• Rule 15 detects sending AppleEvents to the Finder or Terminal.
• Rule 16 detects Mach lookups for com.apple.pasteboard.1.
• Rule 17 detects writing shell files hidden in ~/ or /etc, such as ~/.zlogin, or /etc/zlogin.

The first two may be intended to detect AppleScript being used to control those browsers, the Finder or to run scripts in Terminal. Rule 16 may also be related to Apple’s recent announcement on controlling access to the pasteboard in macOS 26. Rule 17 concerns settings files commonly used by command shells, readily seen if you reveal hidden files for your Home folder.

These may well be related to Bonzai, and enable Apple to get a better idea of what is going on out here in the wild, and focus its efforts in improving its detection.

XProtect Remediator

Once samples of malware have been obtained, developing and testing new Yara rules to detect it is relatively quick, and often uses AI to accelerate the process. Writing a new scanning module for XProtect Remediator is more complicated, and takes more time. It may well be that an additional Bonzai scanner is already on its way, and might be delivered in a further update in the next couple of weeks, perhaps with some fine-tuning of the new Bastion rules. I’ll be keeping a lookout for those.

Above all, it will be interesting to see what changes are made in third-party security software, and how well those tackle what appears to be novel malware for macOS.

Apple has just released updates to XProtect for all supported versions of macOS, bringing it to version 5304, and to XProtect Remediator for all macOS from Catalina onwards, to version 152. As usual, Apple doesn’t release information about what security issues these updates might add or change.

Yara definitions in this version of XProtect add two private rules for Shebang, to match shell scripts by ‘shebang’, and _golang_macho, to match machos compiled by Golang. There are also 19 new rules for a novel family of what appear to be stealers based on the name BONZAI, including MACOS.BONZAIBONANZA.AUTO, MACOS.BONZAIBONANZA.TAAP, MACOS.BONZAIBONANZA.TAFI, MACOS.BONZAIBONANZA.VACA, MACOS.BONZAIBONANZA.VASN, MACOS.BONZAIBONANZA.FU, MACOS.BONZAIBONANZA.SC, MACOS.BONZAIBARRICADE.PE, MACOS.BONZAIBARRICADE.PA, MACOS.BONZAIBARRICADE.KE, MACOS.BONZAIBLASTER.FU, MACOS.BONZAIBLASTER, MACOS.BONZAIBLASTER.TA, MACOS.BONZAIBONDER.SO, MACOS.BONZAIBONDER.PE, MACOS.BONZAIBONDER.TEPL, MACOS.BONZAIBONDER.LA, MACOS.BONZAIBONDER.FU, and MACOS.BONZAIBANANA.

XProtect Remediator doesn’t change the list of scanner modules.

There are changes to the list of Bastion rule 2 paths, and four new Bastion rules 14-17. These cover sending AppleEvents to browsers, the Finder and Terminal, mach-lookup for com.apple.pasteboard.1, and writing to a long list of shell-related hidden directories in the user’s Home folder.

These are probably the greatest changes to XProtect’s Yara rules and Bastion rules for more than a year.

You can check whether these updates have been installed by opening System Information via About This Mac, and selecting the Installations item under Software.

A full listing of security data file versions is given by SilentKnight and SystHist for El Capitan to Tahoe available from their product page. If your Mac hasn’t yet installed this update, you can force it using SilentKnight or at the command line.

If you want to install these as named updates in SilentKnight, their labels are XProtectPayloads_10_15-152 and XProtectPlistConfigData_10_15-5304.

Sequoia and Tahoe systems only

The XProtect update has already been released for Sequoia and Tahoe via iCloud. If you want to check it manually, use the Terminal command
sudo xprotect check
then enter your admin password. If that returns version 5304 but your Mac still reports an older version is installed, you may be able to force the update using
sudo xprotect update