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CVE-2026-27456 util-linux CVE debrief

A Time-of-Check-Time-of-Use (TOCTOU) vulnerability was identified in the SUID binary /usr/bin/mount from util-linux prior to version 2.41.4. This issue 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.

Vendor
util-linux
Product
Unknown
CVSS
MEDIUM 4.7
CISA KEV
Not listed in stored evidence
Original CVE published
2026-04-03
Original CVE updated
2026-07-24
Advisory published
2026-04-03
Advisory updated
2026-07-24

Who should care

System administrators and users of Linux distributions that utilize util-linux, especially those with /usr/bin/mount having the SUID bit set, should be aware of this vulnerability. This vulnerability could allow local unprivileged users to gain unauthorized read access to root-protected files and block devices.

Technical summary

The mount binary validates the source file path with user privileges but subsequently re-canonicalizes and opens it with root privileges 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.

Defensive priority

Medium priority should be given to patching this vulnerability, as it requires local access and specific conditions to be exploited.

Recommended defensive actions

  • Apply the patch from version 2.41.4 or later
  • Verify and restrict write permissions to directories used in /etc/fstab with user,loop options
  • Monitor for suspicious activities around /usr/bin/mount and /etc/fstab
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record was published on 2026-04-03T22:16:25.400Z and was last modified on 2026-07-24T22:10:00.140Z. The NVD entry is currently Analyzed. Evidence is limited to public sources and may not reflect the full scope or details of the vulnerability. Defenders should verify the impact on their systems and review official advisories for specific guidance.

Official resources

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-04-03T22:16:25.400Z and has not been modified since then. The NVD entry is currently Analyzed.