# CVE-2026-78409

## Summary

- **CVE ID:** CVE-2026-78409
- **Severity:** HIGH
- **CVSS Score:** 7 (CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** CWE-59
- **Published:** Sep 2, 2026
- **Last Modified:** Sep 3, 2026

## 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.

## Affected Products

- Red Hat — Red Hat Hardened Images (2.42.2-3.4.hum1)

## References

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

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.12%
- **EPSS Percentile:** 2.4

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._