CVE-2026-78409
Linux Kernel Mount Subdirectory Symlink Traversal Vulnerability
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.
INFO
Published Date :
Sept. 2, 2026, 4:17 p.m.
Last Modified :
Sept. 2, 2026, 4:17 p.m.
Remotely Exploit :
No
Source :
[email protected]
Affected Products
The following products are affected by CVE-2026-78409
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | MITRE-CVE | ||||
| CVSS 3.1 | HIGH | [email protected] |
Solution
- Update the Linux kernel to a patched version.
- Review and sanitize fstab entries for X-mount.subdir.
- Disable X-mount.subdir if updates are not immediate.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-78409.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-78409 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-78409
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-78409 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-78409 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by [email protected]
Sep. 02, 2026
Action Type Old Value New Value Added 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. Added CVSS V3.1 AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H Added CWE CWE-59 Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/78xxx/CVE-2026-78409.json">CVE-2026-78409</a> Added Reference https://access.redhat.com/security/cve/CVE-2026-78409 Added Reference https://bugzilla.redhat.com/show_bug.cgi?id=2522607 Added Reference https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Sep. 02, 2026
Action Type Old Value New Value Added Reference https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv Added SSVC {'id': 'CVE-2026-78409', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-09-02T15:29:06.011028Z'}