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Fencer Vulns
high 7.0

CVE-2026-78409 json

Util-linux: util-linux: x-mount.subdir detached-tree resolution can escape via intermediate symlinks

published 2026-09-02 2 mo ago modified 2026-11-05 4 d ago also EUVD-2026-70107

cvss
7.0
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 8%
public exploits
0
none known

Summary

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.

Patch / fix

  • Red Hat Red Hat Hardened Images 2.42.2-3.4.hum1
  • util-linux Debian 14 2.42.3-1

debian advisories DEBIAN-CVE-2026-78409

  • uuidd hummingbird 1 2.42.2-3.4.hum1
  • libuuid hummingbird 1 2.42.2-3.4.hum1
  • libblkid hummingbird 1 2.42.2-3.4.hum1
  • libfdisk hummingbird 1 2.42.2-3.4.hum1
  • libmount hummingbird 1 2.42.2-3.4.hum1
  • util-linux hummingbird 1 2.42.2-3.4.hum1
  • liblastlog2 hummingbird 1 2.42.2-3.4.hum1
  • libsmartcols hummingbird 1 2.42.2-3.4.hum1

red hat advisories RHSA-2026:63162

  • util-linux openSUSE Tumbleweed 2.42.3-1.1

opensuse advisories openSUSE-SU-2026:11870-1

  • util-linux Alpine 3.24 2.42.3-r0

alpine advisories ALPINE-CVE-2026-78409

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-78409 updated cvss 7.0

util-linux: util-linux: X-mount.subdir detached-tree resolution can escape via intermediate symlinks

  • Red Hat Hardened Images uuidd 2.42.2-3.4.hum1, libuuid 2.42.2-3.4.hum1, libblkid 2.42.2-3.4.hum1, libfdisk 2.42.2-3.4.hum1, libmount 2.42.2-3.4.hum1, util-linux 2.42.2-3.4.hum1, +6 more
    fixed: vendor fix “Upgrade to util-linux v2.41.6, v2.42.3, or later. Until a fix is applied, do not allow unprivileged /etc/fstab entries that specify X-mount.subdir.” RHSA-2026:63162
  • Red Hat Enterprise Linux 7 uuidd, libuuid, libblkid, libmount, util-linux Red Hat Enterprise Linux 8 uuidd, libuuid, libblkid, libfdisk, libmount, util-linux, +3 more Red Hat Enterprise Linux 9 uuidd, libuuid, libblkid, libfdisk, libmount, util-linux, +6 more Red Hat Enterprise Linux 10 util-linux Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
total
Assessed
2 mo ago

Exploit prediction

0.19% chance of exploitation in the next 30 days, higher than 8% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 7.0 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Red Hat Red Hat Hardened Images
  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 7
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 9
  • Red Hat Red Hat OpenShift Container Platform 4
  • Red Hat Red Hat OpenShift Container Platform 5

Classification

Weakness
  • CWE-59 Improper Link Resolution Before File Access

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.