The X-mount.subdir option uses a detached-tree fast path on Linux 6.15 and later and passes the configured subdirectory to open_tree() with AT_SYMLINK_NOFOLLOW. That flag does not stop intermediate symlink traversal or keep resolution inside the newly mounted filesystem. A local unprivileged user with an fstab-authorized X-mount.subdir entry can attach a host path at the intended mountpoint.

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Fixes

Solution

No solution given by the vendor.


Workaround

Upgrade to util-linux v2.41.6, v2.42.3, or later. Until a fix is applied, do not allow unprivileged /etc/fstab entries that specify X-mount.subdir.

History

Thu, 03 Sep 2026 13:00:00 +0000

Type Values Removed Values Added
References

Thu, 03 Sep 2026 12:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

threat_severity

Important


Wed, 02 Sep 2026 16:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Wed, 02 Sep 2026 10:45:00 +0000

Type Values Removed Values Added
Description The X-mount.subdir option uses a detached-tree fast path on Linux 6.15 and later and passes the configured subdirectory to open_tree() with AT_SYMLINK_NOFOLLOW. That flag does not stop intermediate symlink traversal or keep resolution inside the newly mounted filesystem. A local unprivileged user with an fstab-authorized X-mount.subdir entry can attach a host path at the intended mountpoint.
Title Util-linux: util-linux: x-mount.subdir detached-tree resolution can escape via intermediate symlinks
First Time appeared Redhat
Redhat enterprise Linux
Redhat hummingbird
Redhat openshift
Weaknesses CWE-59
CPEs cpe:/a:redhat:hummingbird:1
cpe:/a:redhat:openshift:4
cpe:/o:redhat:enterprise_linux:10
cpe:/o:redhat:enterprise_linux:7
cpe:/o:redhat:enterprise_linux:8
cpe:/o:redhat:enterprise_linux:9
Vendors & Products Redhat
Redhat enterprise Linux
Redhat hummingbird
Redhat openshift
References
Metrics cvssV3_1

{'score': 7, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: redhat

Published:

Updated: 2026-09-03T12:50:56.499Z

Reserved: 2026-08-24T14:40:18.012Z

Link: CVE-2026-78409

cve-icon Vulnrichment

Updated: 2026-09-02T15:29:54.053Z

cve-icon NVD

Status : Received

Published: 2026-09-02T16:17:23.833

Modified: 2026-09-03T13:06:09.800

Link: CVE-2026-78409

cve-icon Redhat

Severity : Important

Publid Date: 2026-09-02T00:00:00Z

Links: CVE-2026-78409 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-09-03T13:15:04Z

Weaknesses