CVE-2026-76642

Description

When an external mount. helper runs but exits with a nonzero status, libmount still treats the helper invocation as successful and runs privileged post-mount hooks. A local unprivileged user with an /etc/fstab entry that uses the user option together with X-mount.idmap or X-mount.owner/group/mode can cause those hooks to clone or re-own the underlying filesystem after the helper fails, leading to local privilege escalation.

Statement

Affected versions: util-linux v2.39 through v2.42.2. Fixed in v2.41.6 and v2.42.3.

Mitigation

Upgrade to util-linux v2.41.6, v2.42.3, or later. Until a fix is applied, avoid combining the user (or users) fstab option with X-mount.idmap or X-mount.owner/group/mode on entries that invoke an external mount.<type> helper. Administrators can also remove or restrict user-mountable fstab entries that specify those X-mount.* options.

Common Vulnerability Scoring System (CVSS) Score Details

Info alert:Important note

CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).

The following CVSS metrics and score provided are preliminary and subject to review.

CVSS v3 Score Breakdown

Red HatNVDcve.org
Base Score7.8N/AN/A
Attack VectorLocalN/AN/A
Attack ComplexityLowN/AN/A
Privileges RequiredLowN/AN/A
User InteractionNoneN/AN/A
ScopeUnchangedN/AN/A
ConfidentialityHighN/AN/A
Integrity ImpactHighN/AN/A
Availability ImpactHighN/AN/A

Vector

Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Red Hat CVSS v3 Score Explanation

Deterministic local privilege escalation after a failed external mount helper; no race. Requires a user-mountable fstab entry with X-mount.idmap or X-mount.owner/group/mode. AC:L because exploitation does not depend on winning a race once those options are present.

Understanding the Weakness (CWE)

CWE-390

Integrity,Other

Technical Impact: Varies by Context; Unexpected State; Alter Execution Logic

An attacker could utilize an ignored error condition to place the system in an unexpected state that could lead to the execution of unintended logic and could cause other unintended behavior.

Acknowledgements

Red Hat would like to thank Andreas Gabriel Berbescu (Independent Security Researcher) and Iván Redondo Plaza (Independent Security Researcher) for reporting this issue.

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