Security Experts:

Apple Silently Patched macOS Security Bypass Flaw

Researchers claim Apple has silently patched a macOS vulnerability that can be exploited to bypass one of the operating system’s security features and execute arbitrary JavaScript code without restrictions.

The issue, discovered by Filippo Cavallarin of Italian security firm Segment, has been described as a local JavaScript quarantine bypass flaw and it has been assigned a risk rating of 3/5.

When a file is downloaded from the Internet, macOS places it in “quarantine” by assigning it the extended attribute. This ensures that the user is alerted of the potential security risks before the file is executed.

Cavallarin said he found a way to bypass the file quarantine feature by exploiting DOM-based cross-site scripting (XSS) vulnerabilities in an HTML file named rhtmlPlayer.html, which is stored in the /System/Library/CoreServices folder of the OS.

According to the researcher, this file contains two DOM-based XSS vulnerabilities that can be exploited by hackers via Uniform Resource Identifier (URI) components.

One way to exploit the flaw is to use .webloc files, which allow users to save website addresses to the local system. On macOS, these types of files are automatically opened with the Safari web browser.

The attacker needs to embed the JavaScript code they want executed into a .webloc file, send it to the victim, and convince them to open it. Segment has published a detailed technical advisory and a video showing how an attacker can exploit this vulnerability to steal sensitive data from the targeted device:

The vulnerability is said to affect macOS 10.12, 10.11, 10.10 and likely prior versions of the operating system. The issue was reported to Apple via Beyond Security’s SecuriTeam Secure Disclosure (SSD) program and it was addressed without any mention in macOS High Sierra 10.13, which Apple released earlier this week.

Beyond Security told SecurityWeek that it informed Apple of the flaw on July 27. The company said the tech giant did not respond to its questions regarding the issue in the past two weeks.

SecurityWeek has reached out to Apple for clarifications and will update this article if the company responds.

This is not the only macOS vulnerability disclosed in recent days. Earlier this month, researcher Patrick Wardle demonstrated how unsigned apps can steal data from the Keychain password management system, and how attackers can bypass the Secure Kernel Extension Loading (SKEL) security feature.

Related: Apple Patches Hundreds of Vulnerabilities Across Product Lines

Related: Apple Patches Vulnerabilities Across All Platforms

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.