High severity7.0NVD Advisory· Published Sep 2, 2026· Updated Sep 3, 2026
CVE-2026-78409
CVE-2026-78409
Description
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.
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Affected products
2- Range: Linux 6.15 and later
Patches
Vulnerability mechanics
References
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