CVE-2026-78409
Published:September 02, 2026
Updated:September 22, 2026
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.
Affected Packages
https://github.com/util-linux/util-linux.git (GITHUB):
Affected version(s) >=v2.42 <v2.42.3Fix Suggestion:
Update to version v2.42.3Related Resources (4)
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Contact UsCVSS v4
Base Score:
7.3
Attack Vector
LOCAL
Attack Complexity
HIGH
Attack Requirements
NONE
Privileges Required
LOW
User Interaction
NONE
Vulnerable System Confidentiality
HIGH
Vulnerable System Integrity
HIGH
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
7
Attack Vector
LOCAL
Attack Complexity
HIGH
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
HIGH
Weakness Type (CWE)
Improper Link Resolution Before File Access ('Link Following')
EPSS
Base Score:
0.12