What’s Vulnerable › Vulnerabilities

CVE-2026-76642: util-linux libmount Privilege Escalation via Failed Mount Helper

• Severity: high (CVSS 7.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-03 · updated 2026-09-24
• Weakness: CWE-390

Description

util-linux versions through 2.41.5 and 2.42.2 fail to check mount helper exit status before running post-mount hooks, allowing unprivileged users to execute privileged operations on pre-existing filesystems. Attackers can exploit X-mount.idmap or X-mount.owner hooks to clone filesystems with inherited suid bits or modify target inode permissions after a helper fails, achieving privilege escalation.

Affected products

• util-linux: from 2.39 before 2.41.6; from 2.42 before 2.42.3 — fixed in 2.41.6, 2.42.3

How to fix

Upgrade to a fixed version: util-linux 2.41.6, 2.42.3. Check the vendor advisory for mitigations.

References

• https://github.com/util-linux/util-linux
• https://github.com/util-linux/util-linux/blob/v2.42.2/libmount/src/context_mount.c#L476
• https://github.com/util-linux/util-linux/blob/v2.42.2/libmount/src/context_mount.c#L892
• https://github.com/util-linux/util-linux/commit/1d14676ea70003e9f5b2a6a76af0cadb1190411a
• https://github.com/util-linux/util-linux/commit/a15c00a9e545aa8b9cf6ec0f888ff6c7b3eaeedc
• https://github.com/util-linux/util-linux/commit/f57cea130839c0af8dc0525274267ae4cfd66bbf
• https://github.com/util-linux/util-linux/security/advisories/GHSA-m25x-3hj9-m26f
• https://www.vulncheck.com/advisories/util-linux-libmount-privilege-escalation-via-failed-mount-helper
• https://github.com/util-linux/util-linux/security/advisories/GHSA-m25x-3hj9-m26f

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