CVE-2026-27456 util-linux: TOCTOU Race Condition in util-linux mount(8) - Loop Device Setup

What is CVE-2026-27456?

CVE-2026-27456 is a medium-severity vulnerability in util-linux, published on 3 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

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.

Weakness: CWE-59, CWE-367, CWE-269

Which versions are affected by CVE-2026-27456?

It affects 1 product.

Products include Kernel Util-Linux.

How do I fix CVE-2026-27456?

Upgrade to a fixed version.

Is CVE-2026-27456 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-27456 exists.

Other vulnerabilities in util-linux

• CVE-2015-5224 Race condition in n/a Critical 9.8
• CVE-2018-7738 Command injection in n/a High 7.8
• CVE-2016-2779 Privilege escalation in n/a High 7.8
• CVE-2026-13595 Util-linux: util-linux: heap use-after-free in libblkid nested partition probing Medium 6.8
• CVE-2020-21583 Command injection in n/a Medium 6.7

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as ALPINE-CVE-2026-27456, AZL-81846, BELL-CVE-2026-27456, CLEANSTART-2026-ZQ21115, CLSA-2026-1782989143, DEBIAN-CVE-2026-27456 and 17 more.