CVE-2026-78409CWE-59

CVE-2026-78409

High · published September 2, 2026

CVSS v3.1
7.0
EPSS
0%
Percentile
2.4
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
7.0 · HIGH
Vector
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
CVSS v4.0
Not supplied
EPSS
0.00124 · 2.4th percentile
Weakness
CWE-59 · Improper Link Resolution Before File Access ('Link Following')
Published
2026-09-02T20:17Z
References (5)
https://access.redhat.com/errata/RHSA-2026:63162 · [email protected]https://access.redhat.com/security/cve/CVE-2026-78409 · [email protected]https://bugzilla.redhat.com/show_bug.cgi?id=2522607 · [email protected]https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv · [email protected]https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv · 134c704f-9b21-4f2e-91b3-4a467353bcc0
EPSS history
Timeline
  • 04 SEP 03:44Z
    EPSS moved — → 0%
    epss
  • 02 SEP 15:11Z
    Util-linux: util-linux: x-mount.subdir detached-tree resolution can escape via intermediate symlinks
    cvelistv5