Mac High Sierra hijinks continue: Nasty apps can pull your passwords

Apple still hasn't been able to seal up keychain access hole for unsigned applications

A security shortcoming in earlier versions of OS X has made its way into macOS High Sierra despite an expert's best efforts to highlight the flaw.

Patrick Wardle, of infosec biz Synack, found that unsigned, and therefore untrustworthy, applications running on High Sierra, aka macOS 10.13, were able to quietly access sensitive information – including stored passwords and keys – without any notification to the user. Normally, apps, even signed trusted ones, trigger a prompt to appear on screen when touching the operating system's Keychain database of saved passphrases and other secrets.

In a short video, Wardle showed how his proof-of-concept unsigned app was able to lift the highly personal information on an updated High Sierra Mac. Wardle said he provided Apple the software and details of the flaw earlier this month, but a fix could not be deployed in time for this week's official High Sierra release. Wardle said a patch is likely in the works.

Still, the researcher reckoned the app should serve as a note of caution to anyone who regularly installs and runs applications downloaded from the internet on their Mac. Even legitimate apps, he noted, could possibly be compromised to exploit the vulnerability.

"Obviously, random apps should not be able to access the entire keychain and dump things like plaintext passwords," Wardle explained this week. "In fact, even signed Apple utilities (ie, /usr/bin/security) that are designed to legitimately access the keychain explicitly require user approval; or most authenticate (with the user's password) before they are allowed to retrieve sensitive keychain data."

This is not the first time the Synack researcher has poked holes in Apple's handling of software permissions. In 2015, Wardle was credited with discovering weaknesses that would let an attacker circumvent the security protections in Apple's app checker, the OS X Gatekeeper.

This is also not the first major security hole to be uncovered in the day-old High Sierra macOS.

Last week, as the OS was nearing its formal release, Wardle revealed that a flaw in the Security Kernel Extension Loading (SKEL) security tool allowed its protections to be easily bypassed, potentially leaving users vulnerable to low-level infections such as rootkits.

It goes without saying that macOS users should avoid running unsigned applications, and disable their execution from the system control panel. Essentially, the take-home here is: don't run unsigned apps. And if you or your friends or family really must do so, be mindful that even untrusted software can exfiltrate sensitive information that applications typically shouldn't have access to without your permission. ®

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