CVE-2026-27456
MediumCVSS 4.7Exploitation Probability (EPSS)
Low risk2th percentile - higher than 2% of all known CVEs
Summary
In util-linux prior to version 2.41.4, a TOCTOU vulnerability has been identified in the SUID binary /usr/bin/mount. When setting up loop devices, mount validates the source file path with user privileges but later re-canonicalizes and opens it with root privileges without verifying that the path has not been replaced. A local unprivileged user can replace the source file with a symlink pointing to any root-owned file or device.
Risk Assessment
An attacker can gain unauthorized read access to root-protected files and block devices, including backup images, disk volumes, and any file containing a valid filesystem. Exploitation requires an /etc/fstab entry with user,loop options and the SUID bit set on /usr/bin/mount.
Recommendation
Immediately update util-linux to version 2.41.4. Also review /etc/fstab entries and consider removing the SUID bit from /usr/bin/mount if not required.
Original NVD description (English source)
util-linux is a random collection of Linux utilities. Prior to version 2.41.4, a TOCTOU (Time-of-Check-Time-of-Use) vulnerability has been identified in the SUID binary /usr/bin/mount from util-linux. The mount binary, when setting up loop devices, validates the source file path with user privileges via fork() + setuid() + realpath(), but subsequently re-canonicalizes and opens it with root privileges (euid=0) without verifying that the path has not been replaced between both operations. Neither O_NOFOLLOW, nor inode comparison, nor post-open fstat() are employed. This allows a local unprivileged user to replace the source file with a symlink pointing to any root-owned file or device during the race window, causing the SUID binary to open and mount it as root. Exploitation requires an /etc/fstab entry with user,loop options whose path points to a directory where the attacker has write permission, and that /usr/bin/mount has the SUID bit set (the default configuration on virtually all Linux distributions). The impact is unauthorized read access to root-protected files and block devices, including backup images, disk volumes, and any file containing a valid filesystem. This issue has been patched in version 2.41.4.