CVE-2026-78409
That flag does not stop intermediate symlink traversal or keep resolution inside the newly mounted filesystem.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.12%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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 3.1
- 7.0 HIGHCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 0.12% probability · 2th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-59
- Source
- secalert@redhat.com
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
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.