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macOS High Sierra Update Patches Keychain Access Flaw

An update released on Thursday by Apple for its macOS High Sierra operating system patches two vulnerabilities, including one that allows malicious applications to steal passwords from the Keychain.

The Keychain flaw, tracked as CVE-2017-7150, was disclosed last week by Patrick Wardle, director of research at Synack. Apple has now addressed the issue with the release of High Sierra 10.13 Supplemental Update.

The researcher warned that High Sierra and previous versions of macOS are affected by a security hole that can be exploited by unsigned applications to programmatically dump and exfiltrate sensitive data from the Keychain, including plaintext passwords. However, he only released a video demonstrating the attack, without making any technical details public.

“A method existed for applications to bypass the keychain access prompt with a synthetic click. This was addressed by requiring the user password when prompting for keychain access,” Apple said in its advisory.

SecurityWeek has reached out to Wardle to find out if the latest update properly patches the vulnerability he found. This article will be updated once the researcher responds.

Wardle also demonstrated recently how Apple's new Secure Kernel Extension Loading (SKEL) security feature, introduced in High Sierra, can be easily bypassed.

The High Sierra 10.13 Supplemental Update also fixes a password disclosure issue involving encrypted Apple File System (APFS) volumes.

Brazil-based developer Matheus Mariano discovered that passwords set by users via Disk Utility for new encrypted APFS volumes are displayed in clear text via the “Show Hint” button when the volume is mounted. The problem only appears to affect encrypted APFS volumes created via Disk Utility.

“This was addressed by clearing hint storage if the hint was the password, and by improving the logic for storing hints,” Apple said about the flaw, which it tracks as CVE-2017-7149.

Apple has also published a knowledge base article for the password leakage issue. The company has advised users to protect their existing APFS volumes by creating a backup, erasing the existing volume, and restoring the initial volume to set a new password.

“Changing the password on an affected volume clears the hint but doesn’t affect the underlying encryption keys that protect the data,” Apple said.

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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.