High [CVE-2026-76642] failed external mount helper still runs privileged X-mount post-hooks
This high-severity Red Hat Linux advisory covers CVE-2026-76642 affecting Red Hat Enterprise Linux 10, Red Hat Hardened Images, Red Hat package: util-linux.
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Summary
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. Affected versions: util-linux v2.39 through v2.42.2.
Fixed in v2.41.6 and v2.42.3. Red Hat severity: Important — CVSS 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H).
Weakness: CWE-390. Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Hardened Images.
Red Hat lists Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9; Red Hat OpenShift Container Platform 4 as not affected. Red Hat does not currently list a fixing RHSA for this CVE.
Affected products named by the advisory: Red Hat package: util-linux.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 51 minutes ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 51 minutes ago·verify at source
Mitigation checklist
- 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.
Official advisory · high-confidence parse· fetched 51 minutes ago·verify at source
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