Gvfs: gvfs-admin socket ownership race permits local root

Overview

A flaw was found in the admin backend of gvfs. The privileged gvfsd-admin daemon changes the ownership of newly created private D-Bus sockets by calling the link-following chown() function on a pathname inside a user-controlled directory. A local attacker can exploit this via a Time-of-Check Time-of-Use (TOCTOU) race condition and exchange the socket pathname with a symbolic link pointing to an arbitrary root-owned file (such as /etc/pam.d/su). The daemon subsequently follows the symlink and changes the ownership of the targeted root-owned file to the attacker's user ID. This allows an authenticated local attacker to modify critical system files, leading to a full local privilege escalation to root.

Affected

• gvfs >= 1.48.1 < 1.62.0
• gvfs >= 1.48.1 < 1.60.3
• gvfs >= 1.48.1 < 1.58.5
• gvfs (all versions)
• gvfs (all versions)
• gvfs (all versions)
• gvfs (all versions)
• gvfs (all versions)

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Workarounds

To mitigate this issue, adjust Polkit rules to require password authentication to start gvfsd-admin or remove execute permissions of the gvfsd-admin binary to prevent execution.