| Name | CVE-2026-78409 |
| 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. |
| Source | CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more) |
Vulnerable and fixed packages
The table below lists information on source packages.
| Source Package | Release | Version | Status |
|---|
| util-linux (PTS) | bookworm | 2.38.1-5+deb12u3 | fixed |
| bookworm (security) | 2.38.1-5+deb12u1 | fixed |
| trixie (security), trixie | 2.41.5-0+deb13u1 | vulnerable |
| forky, sid | 2.42.4-1 | fixed |
The information below is based on the following data on fixed versions.
| Package | Type | Release | Fixed Version | Urgency | Origin | Debian Bugs |
|---|
| util-linux | source | bookworm | (not affected) | | | |
| util-linux | source | (unstable) | 2.42.3-1 | | | |
Notes
[trixie] - util-linux <no-dsa> (Minor issue)
[bookworm] - util-linux <not-affected> (Vulnerable code not present, added in v2.42)
https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv