Apple has released a security update to fix the vulnerability in macOS Big Sur 11.3 and to block malware campaigns that actively abuse it. It fixes a zero-day vulnerability in macOS that is exploited in the wild by Shlayer malware to bypass Apple’s file quarantine, gatekeeper, and even notary security checks.
With the new update, users are now advised that malicious apps “cannot be opened because the developer cannot be identified.” They are also advised to eject the mounted disk image because it may contain malware.
Whereas in the past, the creators of Shlayer succeeded in getting their malicious payloads through Apple’s automated notarization process, passing Apple’s automated security audit means that macOS apps are allowed by Gatekeeper to run macOS security functionality on the system.
Shlayer also used a two-year-old technique to extend privileges and disable macOS ‘Gatekeeper while executing unsigned second-stage payloads in a campaign detected by Carbon Black’s Threat Analysis Unit. According to security expert Patrick Wardle, the bug that has now been fixed will exploit gatekeepers logic flaws in the way it verifies that app packages have been notarized to run on fully patched macOS systems.
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