Security

Apple fixed macOS flaw that could allow to bypass Gatekeeper security feature

Apple recently addressed fixed a flaw in the macOS that could be potentially exploited by an attacker to bypass Gatekeeper security feature.

Apple recently addressed a vulnerability in the macOS operating system, tracked as CVE-2021-30853, that could be potentially exploited by an attacker to bypass the Gatekeeper security feature and run arbitrary code. The vulnerability was reported to Apple by Gordon Long of Box and addressed the flaw with the release of macOS 11.6 updates on September 20, 2021. According to the security advisory published by Apple, this issue was addressed with improved checks.

“A malicious application may bypass Gatekeeper checks.” reads the advisory. “This issue was addressed with improved checks.

A malicious code could bypass automated notarization security checks, which scan for malicious components in the applications, and could be launched by Gatekeeper.

The popular white-hat hacker Patrick Wardle, analyzed the vulnerability and explained why it is so dangerous.

Wardle pointed out that the bug is very intriguing, its exploitation could allow bypassing also File Quarantine, and macOS’s recent notarization requirements.

The experts explained that an attacker can trigger the flaw by tricking the victims into opening a malicious application masqueraded as a harmless PDF, that could be sent to them via email.

Wardle explained that the root cause is that an unsigned, non-notarized script-based application can not explicitly specify an interpreter.

“The astute reader may have noticed that though the script started with the familiar #! (“Shebang”), it is missing an interpreter such as /bin/bash. However when launched, macOS seems to handle this without issue, and still executed the script.” reads post published by Wardle. “Though the process monitor output confirms that macOS will execute the “interpreter-less” script via bash, that fact that no interpreter was specified is ultimately what triggers a (rather nuanced) bug in the kernel. A bug, that allows the PoC to execute without being subjected to File Quarantine, Gatekeeper, nor notarization checks!”

shebang (#!) interpreter directive (e.g. #!/bin/sh or #!/bin/bash) is used to parse and interpret a shell. A malicious application used to exploit this issue can incorporate the shebang line missing an interpreter (i.e., #!) to get the underlying operating system to attempt to execute the script without raising any alert.

“The syspolicyd daemon will perform various policy checks and ultimately prevent the execution of untrusted applications, such as those that are unsigned or unnotarized,” continues the researcher. “But, what if the AppleSystemPolicy kext decides that the syspolicyd daemon does not need to be invoked? Well then, the process is allowed! And if this decision is made incorrectly, well then, you have a lovely File Quarantine, Gatekeeper, and notarization bypass.”

This is not the first issue in macOS that was discovered by researchers and that would enable attackers to bypass the security features implemented by the Apple operating system.

In April, Apple fixed a zero-day vulnerability, tracked as CVE-2021-30657, exploited by Shlayer malware to bypass Apple’s security features and deliver second-stage malicious payloads.

In October, Microsoft discovered a vulnerability in macOS, dubbed Shrootless (CVE-2021-30892), that can allow attackers to bypass System Integrity Protection (SIP) and perform malicious activities, such as gaining root privileges and installing rootkits on vulnerable devices.

Follow me on Twitter: @securityaffairs and Facebook

[adrotate banner=”9″][adrotate banner=”12″]

Pierluigi Paganini

(SecurityAffairs – hacking, Gatekeeper)

[adrotate banner=”5″]

[adrotate banner=”13″]

Pierluigi Paganini

Pierluigi Paganini is member of the ENISA (European Union Agency for Network and Information Security) Threat Landscape Stakeholder Group and Cyber G7 Group, he is also a Security Evangelist, Security Analyst and Freelance Writer. Editor-in-Chief at "Cyber Defense Magazine", Pierluigi is a cyber security expert with over 20 years experience in the field, he is Certified Ethical Hacker at EC Council in London. The passion for writing and a strong belief that security is founded on sharing and awareness led Pierluigi to find the security blog "Security Affairs" recently named a Top National Security Resource for US. Pierluigi is a member of the "The Hacker News" team and he is a writer for some major publications in the field such as Cyber War Zone, ICTTF, Infosec Island, Infosec Institute, The Hacker News Magazine and for many other Security magazines. Author of the Books "The Deep Dark Web" and “Digital Virtual Currency and Bitcoin”.

Recent Posts

Meta plans to train AI on EU user data from May 27 without consent

Meta plans to train AI on EU user data from May 27 without consent; privacy…

5 hours ago

AI in the Cloud: The Rising Tide of Security and Privacy Risks

Over half of firms adopted AI in 2024, but cloud tools like Azure OpenAI raise…

7 hours ago

Google fixed a Chrome vulnerability that could lead to full account takeover

Google released emergency security updates to fix a Chrome vulnerability that could lead to full…

8 hours ago

Nova Scotia Power discloses data breach after March security incident

Nova Scotia Power confirmed a data breach involving the theft of sensitive customer data after…

19 hours ago

Coinbase disclosed a data breach after an extortion attempt

Coinbase confirmed rogue contractors stole customer data and demanded a $20M ransom in a breach…

21 hours ago

U.S. CISA adds a Fortinet flaw to its Known Exploited Vulnerabilities catalog

U.S. Cybersecurity and Infrastructure Security Agency (CISA) adds a Fortinet vulnerability to its Known Exploited Vulnerabilities…

1 day ago