CVE-2026-78409
Published: September 5, 2026Last modified: September 15, 2026
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.
Severity score breakdown
| Parameter | Value |
|---|---|
| Base score | 7 |
| Attack Vector | LOCAL |
| Attack complexity | HIGH |
| Privileges required | LOW |
| User interaction | NONE |
| Scope | UNCHANGED |
| Confidentiality | HIGH |
| Integrity impact | HIGH |
| Availability impact | HIGH |
| Vector | CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H |
Status
| Product | Release | Package | Status |
|---|---|---|---|
| Alpaquita Linux | 23 LTS | util-linux | Unknown (2.38.1-r2) |
| 25 LTS | util-linux | Unknown (2.41-r6) | |
| Stream | util-linux | Fixed (2.42.3-r1) | |
| Hardened Containers | 23 LTS | util-linux | Unknown (2.38.1-r2) |
| 25 LTS | util-linux | Unknown (2.41-r6) | |
| Stream | util-linux | Fixed (2.42.3-r1) |