Friday, June 4, 2021

TCC Bypass in XCSSET Malware

Stuart Ashenbrenner, Jaron Bradley, and Ferdous Saljooki (via Juli Clover, Dan Goodin):

In the latest macOS release (11.4), Apple patched a zero-day exploit (CVE-2021-30713) which bypassed the Transparency Consent and Control (TCC) framework. This is the system that controls what resources applications have access to, such as granting video collaboration software access to the webcam and microphone, in order to participate in virtual meetings. The exploit in question could allow an attacker to gain Full Disk Access, Screen Recording, or other permissions without requiring the user’s explicit consent — which is the default behavior. We, the members of the Jamf Protect detection team, discovered this bypass being actively exploited during additional analysis of the XCSSET malware, after noting a significant uptick of detected variants observed in the wild. The detection team noted that once installed on the victim’s system, XCSSET was using this bypass specifically for the purpose of taking screenshots of the user’s desktop without requiring additional permissions.


If any of the appID’s are found on the system, the command returns the path to the installed application. With this information, the malware crafts a custom AppleScript application and injects it into the installed, donor application.


Once all files are in place, the custom application will piggyback off of the parent application, which in the example above is Zoom. This means that the malicious application can take screenshots or record the screen without needing explicit consent from the user. It inherits those TCC permissions outright from the Zoom parent app.

Unfortunately, Apple’s fix does not seem to precisely target the actual vulnerability and introduced more problems.


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