CVE Catalog

CVE-2026-78409

HighCVSS 7.0
Published: Updated: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.12%

2th percentile - higher than 2% of all known CVEs

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.

Risk Assessment

Risk of unauthorized mounting of host paths, potentially leading to privilege escalation or filesystem isolation breach.

Recommendation

Update the Linux kernel to a version containing the fix. Restrict the use of X-mount.subdir option in fstab to trusted entries.

Other vulnerabilities in Linux kernel

See all
Original NVD description (English source)

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.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS