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high · CVSS 7

CVE-2026-78409

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

Published 2 Sept 2026 · Source updated 4 Nov 2026 · Retrieved 2026-11-05 00:19 UTC

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What happened?

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.

Description supplied by CVE Program. Formatting is simplified; follow the original advisory for full details.

Affected software and versions

Source-provided software and version information
SoftwareVersion informationFixed version
util-linux-mainRed Hatunaffected: 2.42.2-3.4.hum1 to < *See vendor advisory
util-linuxRed HatDefault status: unaffectedSee vendor advisory
util-linuxRed HatDefault status: unaffectedSee vendor advisory
util-linuxRed HatDefault status: unaffectedSee vendor advisory
rhel8/flatpak-runtimeRed HatDefault status: unaffectedSee vendor advisory
rhel8/flatpak-sdkRed HatDefault status: unaffectedSee vendor advisory
util-linuxRed HatDefault status: unaffectedSee vendor advisory
openshift/ose-rhel-coreos-8Red HatDefault status: unaffectedSee vendor advisory
openshift/ose-rhel-coreos-9Red HatDefault status: unaffectedSee vendor advisory
openshift/ose-rhel-coreos-9Red HatDefault status: unaffectedSee vendor advisory

Version information comes from the source record and can include unaffected products and exceptions. Distribution packages may contain backported fixes: an older upstream version alone does not prove a server is affected.

Is it being exploited?

This CVE was not listed in the CISA catalogue at our last retrieval. This does not establish that exploitation is absent.

CISA data retrieved 2026-11-06 16:38 UTC. Check CISA ↗

How to respond

  1. Confirm the product, installed package version, and any configuration requirements in the vendor advisory.
  2. Follow the vendor’s remediation or workaround guidance in the references below. Structured fixed-version data is unavailable here; the publisher’s description may include a fix or workaround.
  3. Restart affected services if required, then verify the running version. Known exploitation may warrant investigation as well as patching.

Sources and remediation references

This public advisory does not determine whether a particular server is affected. Records are refreshed as sources change; verify urgent decisions against the original advisory.

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