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util-linux CVE-2026-78409

| EUVDEUVD-2026-70107 HIGH
Improper Link Resolution Before File Access (CWE-59)
2026-09-02 redhat
Red Hat Red Hat Enterprise Linux 10 Red Hat Enterprise Linux 7 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 9 Red Hat Openshift Container Platform 4 Suse Red Hat Hardened Images Red Hat
7.0
CVSS 3.1 · Vendor: redhat
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Severity by source

Vendor (redhat) PRIMARY
7.0 HIGH
AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
vuln.today AI
7.8 HIGH

Local attack with two required preconditions (AC:H); in container/OpenShift context mount escape crosses to host scope (S:C), warranting a scope-changed vector over the provided S:U.

3.1 AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
4.0 AV:L/AC:H/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
SUSE
7.8 HIGH
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Red Hat
7.0 HIGH
qualitative

Primary rating from Vendor (redhat).

CVSS VectorVendor: redhat

Attack Vector
Local
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

4
POC Analysis Generated
Sep 08, 2026 - 23:28 vuln.today
Metadata Corrected
Sep 02, 2026 - 16:40 vuln.today
tag: Information Disclosure replaced by Privilege Escalation
Analysis Generated
Sep 02, 2026 - 16:02 vuln.today
CVE Published
Sep 02, 2026 - 15:11 cve.org
HIGH 7.0

DescriptionCVE.org

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.

AnalysisAI

Symlink traversal in util-linux's X-mount.subdir mount option allows a local unprivileged user with an fstab-authorized entry to redirect mount resolution to arbitrary host paths, achieving privilege escalation or container escape on Linux 6.15+ kernels. The root cause is that AT_SYMLINK_NOFOLLOW, passed to open_tree() in the detached-tree fast path, only blocks final-component symlinks - not intermediate path components - leaving an attacker who can plant a symlink in a middle directory able to substitute the intended subdirectory with any host path. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Vulnerability AssessmentAI

Exploitation Three specific conditions must all be met: (1) the target host must be running Linux kernel 6.15 or later, specifically the code path that uses open_tree() for X-mount.subdir - earlier kernels use a different implementation that may not be affected; (2) /etc/fstab must contain an entry authorizing the attacker's user or group to perform a mount using the X-mount.subdir option, which is a non-default configuration requiring explicit administrator action; and (3) the attacker must be able to replace or create a symlink at an intermediate component of the configured subdirectory path prior to the mount operation, requiring write access to that intermediate directory. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment CVSS 7.0 with AV:L/AC:H/PR:L reflects real constraints: the attack is local-only and requires two preconditions - a pre-existing fstab-authorized X-mount.subdir entry and attacker control over an intermediate path component. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation No confirmed patched release version is available at time of analysis; the upstream GitHub advisory (https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv) and Red Hat's advisory (https://access.redhat.com/security/cve/CVE-2026-78409) should be monitored for patch releases and applied immediately when available. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours, identify all systems running RHEL 7-10 or OpenShift 4 on Linux 6.15+ kernels and audit fstab configurations for X-mount.subdir mount entries; document which applications depend on this mount option. …

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SLES15-SP5-CHOST-BYOS-SAP-CCloud Not-Affected
SLES15-SP6-CHOST-BYOS Not-Affected
SLES15-SP6-CHOST-BYOS-Aliyun Not-Affected
SLES15-SP6-CHOST-BYOS-Azure Not-Affected
SLES15-SP6-CHOST-BYOS-EC2 Not-Affected

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CVE-2026-78409 vulnerability details – vuln.today
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