IT Pro is supported by its audience. When you purchase through links on our site, we may earn an affiliate commission. Learn more

Critical macOS vulnerability found to bypass SIP restrictions

The flaw lies in how the OS handles software packages and post-installation scripts

Screen of code displaying Microsoft's proof of concept for the Shrootless exploit on macOS

Security researchers at Microsoft have discovered a flaw in Apple’s macOS that can hackers could use to bypass the System Integrity Protection (SIP) feature and execute arbitrary code.

Dubbed Shrootless, the flaw has been identified as CVE-2021-30892 and was included in the security updates released by Apple on 26 October.

The flaw lies in how Apple signs the software package and how the post-installation scripts are installed in it. The researchers found that attackers can use this mechanism for malicious purposes by creating a custom package that can intercept the installation process. After SIP bypass, an attacker can install rootkits and undetectable malware, and even overwrite system files.

A design flaw means that in some cases software packages require access to directories protected by SIP, as is the case with system updates. Files with the extended attribute 'com.apple.rootless' are similarly SIP-protected. Of course, there’s no way to add that extended attribute to a file legitimately, otherwise malware could use SIP for its own protection. 

While analyzing macOS processes to bypass SIP, researchers came across the 'system_installd' daemon with powerful 'com.apple.rootless.install.inheritable' rights. With these rights, any 'system_installd' child process can avoid all SIP-set file system restrictions.

Related Resource

The top three IT pains of the new reality and how to solve them

Driving more resiliency with unified operations and service management

Man at his computer next to title card - whitepaper from ServiceNowFree download

The researchers decided to examine all the child processes of 'system_installd' and were surprised to find several cases that allow hackers to abuse this functionality to bypass SIP.

For example, if an Apple-signed package (.pkg file) is installed, the package will start the 'system_installd' process, which is responsible for installing it. If the package contains any post-installation scripts, 'system_installd' starts them by initiating the default shell (on macOS, this is zsh).

It's important to note that after starting zsh, it then looks for the '/etc/zshenv' file and, if found, automatically runs commands from it, even in a non-interactive mode. Therefore, to perform arbitrary operations on the device, attackers can create a malicious '/etc/zshenv' file and then wait for 'system_installd' to invoke zsh.

Researchers said that the research underscores the importance of collaboration among security researchers, software vendors, and the larger security community.

“As cross-platform threats continue to increase, vulnerability discoveries, coordinated response, and other forms of threat intelligence sharing help enrich our protection technologies that secure users’ computing experience regardless of the platform or device they’re using,” said Jonathan Bar Or, senior security researcher at Microsoft’s 365 Defender Research Team.

Featured Resources

Four strategies for building a hybrid workplace that works

All indications are that the future of work is hybrid, if it's not here already

Free webinar

The digital marketer’s guide to contextual insights and trends

How to use contextual intelligence to uncover new insights and inform strategies

Free Download

Ransomware and Microsoft 365 for business

What you need to know about reducing ransomware risk

Free Download

Building a modern strategy for analytics and machine learning success

Turning into business value

Free Download

Recommended

Microsoft to double salary budget to retain workers
Careers & training

Microsoft to double salary budget to retain workers

17 May 2022
Microsoft warns of new botnet variant targeting Windows and Linux systems
Security

Microsoft warns of new botnet variant targeting Windows and Linux systems

16 May 2022
The Total Economic Impact™ of Apple Mac in Enterprise: M1 update
Whitepaper

The Total Economic Impact™ of Apple Mac in Enterprise: M1 update

12 May 2022
Windows Server admins say latest Patch Tuesday broke authentication policies
Server & storage

Windows Server admins say latest Patch Tuesday broke authentication policies

12 May 2022

Most Popular

Windows Server admins say latest Patch Tuesday broke authentication policies
Server & storage

Windows Server admins say latest Patch Tuesday broke authentication policies

12 May 2022
Russian hackers declare war on 10 countries after failed Eurovision DDoS attack
hacking

Russian hackers declare war on 10 countries after failed Eurovision DDoS attack

16 May 2022
IT admin deletes company’s databases and is jailed for seven years
Policy & legislation

IT admin deletes company’s databases and is jailed for seven years

16 May 2022