CVE-2026-78409

Util-linux: util-linux: x-mount.subdir detached-tree resolution can escape via intermediate symlinks

Published Sep 2, 2026 CVSS 3.1 · 7 High EPSS < 1% KEV · Not listed
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.

Remediation

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.

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
First Time appeared Redhat rhel Els
CPEs cpe:/o:redhat:enterprise_linux:10
cpe:/o:redhat:enterprise_linux:7
cpe:/o:redhat:enterprise_linux:8
cpe:/o:redhat:enterprise_linux:9
cpe:/a:redhat:enterprise_linux:10
cpe:/a:redhat:enterprise_linux:8
cpe:/a:redhat:enterprise_linux:9
cpe:/a:redhat:openshift:5
cpe:/o:redhat:rhel_els:7
Vendors & Products Redhat rhel Els
Type Values Removed Values Added
First Time appeared Linux
Linux util-linux
Redhat hardened Images
Redhat openshift Container Platform
Vendors & Products Linux
Linux util-linux
Redhat hardened Images
Redhat openshift Container Platform
Type Values Removed Values Added
Metrics ssvc

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

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'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
redhat
Published
Updated
Nov 4, 2026, 11:37 PM
Reserved
Aug 24, 2026, 2:40 PM
Status
Awaiting Analysis
Published
Sep 2, 2026, 4:17 PM
Modified
Nov 5, 2026, 12:17 AM
Severity
Important
Public date
Sep 2, 2026, 12:00 AM