Util-linux: util-linux: x-mount.subdir detached-tree resolution can escape via intermediate symlinks
Priority HIGH 66CWE-59Published · Updated
Key facts
- Attack vector
- Local
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- High
- Impact type
- —
- Confidentiality · integrity · availability
- High · High · High
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat.
Summary
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.
Why it matters now
Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00189 8th percentileScored 2026-11-07
Fix Fixed Red Hat: 1 advisory
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- No
- Technical impact
- Total
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Red Hat | Red Hat Hardened Images | — | 2.42.2-3.4.hum1 | Patch available | CNA |
| Red Hat | Red Hat Enterprise Linux 10 | — | — | Not affected | CNA |
| Red Hat | Red Hat Enterprise Linux 7 | — | — | Not affected | CNA |
| Red Hat | Red Hat Enterprise Linux 8 | — | — | Not affected | CNA |
| Red Hat | Red Hat Enterprise Linux 9 | — | — | Not affected | CNA |
| Red Hat | Red Hat Enterprise Linux 9 | — | — | Not affected | CNA |
| Red Hat | Red Hat Enterprise Linux 9 | — | — | Not affected | CNA |
| Red Hat | Red Hat OpenShift Container Platform 4 | — | — | Not affected | CNA |
| Red Hat | Red Hat OpenShift Container Platform 4 | — | — | Not affected | CNA |
| Red Hat | Red Hat OpenShift Container Platform 5 | — | — | Not affected | CNA |
- Red Hat Hardened Images VendorRed Hat Affected — Fixed in 2.42.2-3.4.hum1 Patch available CNA
- Red Hat Enterprise Linux 10 VendorRed Hat Affected — Fixed in — Not affected CNA
- Red Hat Enterprise Linux 7 VendorRed Hat Affected — Fixed in — Not affected CNA
- Red Hat Enterprise Linux 8 VendorRed Hat Affected — Fixed in — Not affected CNA
- Red Hat Enterprise Linux 9 VendorRed Hat Affected — Fixed in — Not affected CNA
- Red Hat Enterprise Linux 9 VendorRed Hat Affected — Fixed in — Not affected CNA
- Red Hat Enterprise Linux 9 VendorRed Hat Affected — Fixed in — Not affected CNA
- Red Hat OpenShift Container Platform 4 VendorRed Hat Affected — Fixed in — Not affected CNA
- Red Hat OpenShift Container Platform 4 VendorRed Hat Affected — Fixed in — Not affected CNA
- Red Hat OpenShift Container Platform 5 VendorRed Hat Affected — Fixed in — Not affected CNA
CPE names CNA · 7
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:/a:redhat:hummingbird:1 | 1 | — | Red Hat |
| cpe:/a:redhat:enterprise_linux:10 | 10 | — | Red Hat |
| cpe:/o:redhat:rhel_els:7 | 7 | — | Red Hat |
| cpe:/a:redhat:enterprise_linux:8 | 8 | — | Red Hat |
| cpe:/a:redhat:enterprise_linux:9 | 9 | — | Red Hat |
| cpe:/a:redhat:openshift:4 | 4 | — | Red Hat |
| cpe:/a:redhat:openshift:5 | 5 | — | Red Hat |
- cpe:/a:redhat:hummingbird:1 Versions 1 — ·Red Hat
- cpe:/a:redhat:enterprise_linux:10 Versions 10 — ·Red Hat
- cpe:/o:redhat:rhel_els:7 Versions 7 — ·Red Hat
- cpe:/a:redhat:enterprise_linux:8 Versions 8 — ·Red Hat
- cpe:/a:redhat:enterprise_linux:9 Versions 9 — ·Red Hat
- cpe:/a:redhat:openshift:4 Versions 4 — ·Red Hat
- cpe:/a:redhat:openshift:5 Versions 5 — ·Red Hat
Remediation
Red Hat 1 advisory
- RHSA-2026:63162 Released 2026-09-03 · Red Hat rating ImportantRed Hat Hardened Images RPMs Security Update
- Red Hat Hardened Images libblkid-2.42.2-3.4.hum1@aarch64, libblkid-2.42.2-3.4.hum1@x86_64, libblkid-devel-2.42.2-3.4.hum1@aarch64 +34
Fixed in the same release
Records fixed by the same vendor advisory or release, as the CNA lists them.
- Advisory ·
Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7 and 5 more products — RHSA-2026:63162
3 records Highest priority Priority HIGH 3 HIGH
Other records, highest priority first
- TI-2026-54523 Util-linux: util-linux: restricted bind mounts do not pin the source, allowing x-mount.owner/group/mode redirectionPriority HIGH 69
- TI-2026-54521 Util-linux: util-linux: nsenter --join-cgroup leaks root cgroup migration authorityPriority HIGH 68
Vendor assessments
Red Hat
Red Hat rating: Important. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Hardened Images | Fixed | RHSA-2026:63162 |
Not affected: 6 products
- 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
- Red Hat OpenShift Container Platform 5
Timeline
- 2026-10-02 Threatist record created from CVE-2026-78409
- 2026-10-21 Affected versions changed · CNA
- 2026-11-04 Affected versions changed · CNA
- 2026-11-05 Affected versions changed · Red Hat
References
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- TI-2018-16080 A code execution vulnerability exists in the Stapler web framework used by Jenkins 2.153… KEVCVSS 3.1CRITICAL 9.8
Sources
- CVE-2026-78409 · CVE Program
- CVE-2026-78409 · NVD
- FIRST EPSS
- CVE-2026-78409 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences