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Vulnerability record · CVE-2026-78409 · published 2 September 2026

CVE-2026-78409: Link following vulnerability

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.

7.0 CVSS 3.1 High EPSS 0.15% · top 96.2% CWE-59 · Link following Awaiting Analysis
7.0CVSS 3.1 base score
0.15%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
5References
3 Sep 2026Last modified by NVD

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.

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

References

LinkTags
https://access.redhat.com/errata/RHSA-2026:63162
https://access.redhat.com/security/cve/CVE-2026-78409
https://bugzilla.redhat.com/show_bug.cgi?id=2522607
https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv
https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv

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Source: NIST National Vulnerability Database (record CVE-2026-78409), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.