Util linux: The X-mount.subdir option uses a detached-tree fast path on Linux 6.15 and later and passes the configured
Affects util-linuxSource GCVE Database
Not known to be exploited · CVSS 7.0 High · fixed in 2.41.6 : patch util-linux soon.
Data as of 9 Nov 2026, 13:54 UTC
Thin evidence
One scorer or none| CNA (redhat) | CVSS 3.1 | 7.0 |
|---|
- Patch
- Available – fixed in 2.41.6
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 2 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 9 Nov 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 26.10util-linuxpkg:deb/ubuntu/util-linux?arch=source&distro=stonkingOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSutil-linuxpkg:deb/ubuntu/util-linux?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu Pro 20.04 LTSutil-linuxpkg:deb/ubuntu/util-linux?arch=source&distro=esm-infra/focalOther threats | Affected
| Fixed in– |
Ubuntu 18.04 LTSutil-linuxpkg:deb/ubuntu/util-linux?arch=source&distro=bionicOther threats | Affected
| Fixed in– |
Ubuntu Pro 16.04 LTSutil-linuxpkg:deb/ubuntu/util-linux?arch=source&distro=esm-infra/xenialOther threats | Affected
| Fixed in– |
Ubuntu 14.04 LTSutil-linuxpkg:deb/ubuntu/util-linux?arch=source&distro=trustyOther threats | Affected
| Fixed in– |
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
Upgrade util-linux to version 2.41.6, 2.42.3, or later to apply the official fix. If you cannot patch yet, do not allow unprivileged /etc/fstab entries that specify the X-mount.subdir option. This prevents exploitation by restricting unauthorized mount configurations.
Description
A vulnerability in util-linux's X-mount.subdir option affects versions 2.42 through 2.42.2 when used with Linux kernel 6.15 and later. The issue arises because the open_tree() call uses AT_SYMLINK_NOFOLLOW, which does not prevent traversal of intermediate symlinks, allowing a local unprivileged user with an fstab-authorized X-mount.subdir entry to mount a host path at the intended mountpoint. This can lead to unauthorized file system access and modification.
References
- ubuntu.com/security/CVE-2026-78409 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-78409 (opens in a new tab)
- github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv (opens in a new tab)
- access.redhat.com/security/cve/CVE-2026-78409 (opens in a new tab)
- bugzilla.redhat.com/show_bug.cgi?id=2522607 (opens in a new tab)