Microsoft Particulars Gatekeeper Bypass Vulnerability in Apple macOS Techniques

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Dec 20, 2022Ravie LakshmananEndpoint Safety / Vulnerability

Microsoft has disclosed particulars of a now-patched safety flaw in Apple macOS that could possibly be exploited by an attacker to get round safety protections imposed to forestall the execution of malicious purposes.

The shortcoming, dubbed Achilles (CVE-2022-42821, CVSS rating: 5.5), was addressed by the iPhone maker in macOS Ventura 13, Monterey 12.6.2, and Big Sur 11.7.2, describing it as a logic concern that could possibly be weaponized by an app to bypass Gatekeeper checks.

“Gatekeeper bypasses corresponding to this could possibly be leveraged as a vector for preliminary entry by malware and different threats and will assist improve the success price of malicious campaigns and assaults on macOS,” Jonathan Bar Or of the Microsoft 365 Defender Analysis Workforce said.


Gatekeeper is a security mechanism designed to make sure that solely trusted apps run on the working system. That is enforced by way of an prolonged attribute known as “” that is assigned to recordsdata downloaded from the web. It’s analogous to the Mark of the Net (MotW) flag in Home windows.

Thus when an unsuspecting person downloads a doubtlessly dangerous app that impersonates a bit of official software program, the Gatekeeper characteristic prevents the apps from being run as it isn’t validly signed and notarized by Apple.

Even in situations the place an app is accepted by Apple, customers are displayed a immediate when it is launched for the primary time to hunt their express consent.

Given the essential position performed by Gatekeeper in macOS, it is onerous to not think about the results of sidestepping the security barrier, which may successfully allow menace actors to deploy malware on the machines.

The Achilles vulnerability recognized by Microsoft exploits a permission mannequin known as Entry Management Lists (ACLs) so as to add extraordinarily restrictive permissions to a downloaded file (i.e., “everybody deny write,writeattr,writeextattr,writesecurity,chown”), thereby blocking Safari from setting the quarantine prolonged attribute.

In a hypothetical assault situation, an adversary may embrace the approach to craft a rogue app and host it on a server, which may then be delivered to a potential goal through social engineering, malicious advertisements, or a watering gap.

The tactic additionally circumvents Apple’s newly launched Lockdown Mode in macOS Ventura – an opt-in restrictive setting to counter zero-click exploits – necessitating that customers apply the newest updates to mitigate threats.

“Pretend apps stay one of many high entry vectors on macOS, indicating Gatekeeper bypass methods are a beautiful and even a mandatory functionality for adversaries to leverage in assaults,” Bar Or stated.

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