CVE-2026-78409

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 3.1

7.0CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS

0.2% chance of exploitation in the next 30 days; higher than 8% of CVEs (scores of 2026-10-25)

CWE

CWE-59

Published

2026-09-02

Modified

2026-10-21

Record from

the NVD, synced 2026-10-22

References

• https://access.redhat.com/errata/RHSA-2026:63162
• https://access.redhat.com/security/cve/CVE-2026-78409
• https://bugzilla.redhat.com/show_bug.cgi?id=2522607
• https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv
• https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv

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