High severity · published Sep 2, 2026
CVE-2026-78409
Util-linux: util-linux: x-mount.subdir detached-tree resolution can escape via intermediate symlinks
7.0
CVSS
0.2%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Attack vector
Local
Complexity
High
Privileges
Low
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 8% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
RH
Red Hat Hardened Images · Red Hat
All versions, or not specified · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-78409
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-78409
access.redhat.com
https://access.redhat.com/errata/RHSA-2026:63162
access.redhat.com
https://access.redhat.com/security/cve/CVE-2026-78409
bugzilla.redhat.com
https://bugzilla.redhat.com/show_bug.cgi?id=2522607
github.com
https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv
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