high · 7

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

CVE-2026-78409 · published 2 Sept 2026

How serious is it

  • Severity: high, CVSS score 7 out of 10.
  • No exploit prediction (EPSS) score yet.
  • Not on the CISA list of exploited vulnerabilities.
  • No public exploit in Exploit-DB.

Is your app affected by CVE-2026-78409?

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Who is affected

  • 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 Enterprise Linux 9
  • Red Hat Red Hat Enterprise Linux 9
  • Red Hat Red Hat OpenShift Container Platform 4
  • Red Hat Red Hat OpenShift Container Platform 4

How to check

  1. Find out whether you run the affected product and which version, then compare it with the versions above.

How to fix

Copies a prompt for Claude Code, Cursor or Codex that asks it to check whether you run this product.
  1. Apply the vendor's update or mitigation from the references below. If there is none yet, limit exposure of the affected service until there is.
  2. If a vulnerable version was live, check your logs and rotate the secrets that server could read.

The advisory

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.

Check your whole app

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References

Merged from CVE List. Last updated 29 Oct 2026. All vulnerabilities · RSS · JSON

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