Apple has recently released macOS Big Sur 11.3. This update addresses numerous security flaws including a zero-day under attack. As revealed, this zero-day attracted Shlayer malware to target vulnerable macOS devices via Gatekeeper bypass.
Shlayer Malware Exploiting macOS Zero-day
Apple security firm Jamf Protect has shared details of a serious macOS zero-day that a Shlayer malware variant actively exploits.
The vulnerability first caught the attention of researcher Cedric Owens who then reported it to Apple. It was a serious security issue that allowed an adversary with a malicious app to bypass Apple’s security check Gatekeeper.
Elaborating further on this issue, Patrick Wardle explained that a logic issue existed in the way macOS evaluates an app. Due to the bug, the system even allowed unsigned apps to run uninhibited. As stated,
Any script-based application that does not contain an Info.plist file will be misclassified as “not a bundle” and thus will be allowed to execute with no alerts nor prompts.
Wardle has shared how an app could exploit this flaw in his blog post.
Following this discovery, Wardle reached out to Jamf Protect that detected active exploitation of the bug by a Shlayer variant.
Shlayer first caught attention in June 2020 when researchers noticed it actively targeting macOS devices. The malware would easily bypass Apple’s underlying security mechanisms, such as Gatekeeper, Notarization, and File Quarantine.
And now, Jamf detected a Shlayer variant already designed in a way to exploit this logic issue CVE-2021-30657. Thus, the malware now requires no user interaction (such as the right-click limitation of the previous variant) to execute. All it takes is to trick a user into downloading the malicious file on the device and attempting to install it.
The attackers are currently distributing this malware via hacked and phishing websites appearing in Google SERPs.
Another Gatekeeper Also Fixed With Other Bugs
In addition to the above, one more Gatekeeper bypass bug has also received a fix with macOS Big Sur 11.3.
This vulnerability caught the attention of F-Secure researcher Rasmus Sten who then reported it to Apple.
Elaborating on this flaw in a blog…