CVE-2026-78409

HIGHPre-NVD 7.07.0—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.0 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.1%, top 98% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
Trending — 3 sources updated this weekElevated
7.0EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 7.0Exploit: Elevated riskExposed: 0

A fix is available — apply it.

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 v3
7.0
EG Score
7.0(medium)
EG Risk
48(Track*)
EG Risk 48/100SSVC: Track*

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity70% × 45%
Exploitation40% × 40%
Automatability0% × 15%
Action: Watch closely — could escalate to Attend.
EPSS PROB
0%
EPSS %ILE
2%
KEV
Not listed

Published

September 2, 2026

Last Modified

September 3, 2026

Advisory Details (2)

Auto-updated Sep 2, 2026
🔬 Proof of concept available. Patch available. Sources: redhat, github.
github Patch Available🟡 PoC Available

`X-mount.subdir` detached-tree resolution can escape via intermediate symlinks and procfs paths · Advisory · util-linux/util-linux · GitHub

https://github.com/util-linux/util-linux/security/advisories/GHSA-8f2p-47x3-43mv
redhat

2522607 – (CVE-2026-78409) CVE-2026-78409 util-linux: util-linux: X-mount.subdir detached-tree resolution can escape via intermediate symlinks

https://bugzilla.redhat.com/show_bug.cgi?id=2522607

Vendor Advisories for CVE-2026-78409(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(1)

Vendor / EcosystemFixed in / PatchReleasedSource
redhatutil-linux-main-2.42.2-3.4.hum12026-09-03redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(4 across 4 ecosystems)
Alpine:v3.24(1)
PackageVulnerable rangeFixed inDependents
util-linux—2.42.3-r0—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
util-linux2.38.1-5 ... 2.42~rc2-1 (119 versions)——
Debian:13(1)
PackageVulnerable rangeFixed inDependents
util-linux2.41-5 ... 2.42~rc2-1 (35 versions)——
Debian:14(1)
PackageVulnerable rangeFixed inDependents
util-linux2.41-5 ... 2.42~rc2-1 (34 versions)——

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 26× in last 7d / 64× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-19 09:10 UTCVendor advisory
  2. 2026-09-18 21:24 UTCEG score recompute
  3. 2026-09-18 21:24 UTCVendor advisory
  4. 2026-09-18 19:28 UTCEPSS rescore
  5. 2026-09-18 08:39 UTCVendor advisory
  6. 2026-09-17 20:53 UTCEG score recompute
  7. 2026-09-17 20:53 UTCVendor advisory
  8. 2026-09-17 09:07 UTCVendor advisory
  9. 2026-09-16 21:21 UTCEG score recompute
  10. 2026-09-16 21:21 UTCVendor advisory
  11. 2026-09-16 14:08 UTCEPSS rescore
  12. 2026-09-16 09:16 UTCEG score recompute
  13. 2026-09-16 09:16 UTCVendor advisory
  14. 2026-09-16 05:15 UTCEPSS rescore
  15. 2026-09-15 21:30 UTCVendor advisory
  16. 2026-09-15 09:44 UTCEG score recompute
  17. 2026-09-15 09:44 UTCVendor advisory
  18. 2026-09-15 03:12 UTCEPSS rescore
  19. 2026-09-15 03:12 UTCEPSS rescore
  20. 2026-09-14 21:58 UTCVendor advisory
  21. 2026-09-14 10:11 UTCVendor advisory
  22. 2026-09-13 22:25 UTCEG score recompute
  23. 2026-09-13 22:25 UTCVendor advisory
  24. 2026-09-13 10:39 UTCVendor advisory
  25. 2026-09-12 22:53 UTCEG score recompute
Show 39 more
  1. 2026-09-12 22:53 UTCVendor advisory
  2. 2026-09-12 11:06 UTCVendor advisory
  3. 2026-09-11 23:16 UTCEG score recompute
  4. 2026-09-11 23:16 UTCVendor advisory
  5. 2026-09-11 14:53 UTCEPSS rescore
  6. 2026-09-11 14:53 UTCEPSS rescore
  7. 2026-09-11 10:59 UTCEG score recompute
  8. 2026-09-11 10:59 UTCVendor advisory
  9. 2026-09-10 23:13 UTCVendor advisory
  10. 2026-09-10 11:27 UTCEG score recompute
  11. 2026-09-10 11:27 UTCVendor advisory
  12. 2026-09-10 09:35 UTCEPSS rescore
  13. 2026-09-09 23:32 UTCVendor advisory
  14. 2026-09-09 10:59 UTCVendor advisory
  15. 2026-09-08 23:13 UTCEG score recompute
  16. 2026-09-08 23:13 UTCVendor advisory
  17. 2026-09-08 22:01 UTCEPSS rescore
  18. 2026-09-08 04:17 UTCVendor advisory
  19. 2026-09-07 16:30 UTCEG score recompute
  20. 2026-09-07 16:30 UTCVendor advisory
  21. 2026-09-07 04:43 UTCVendor advisory
  22. 2026-09-06 16:58 UTCEG score recompute
  23. 2026-09-06 16:58 UTCVendor advisory
  24. 2026-09-06 13:48 UTCEPSS rescore
  25. 2026-09-06 05:11 UTCVendor advisory
  26. 2026-09-05 17:25 UTCEG score recompute
  27. 2026-09-05 17:25 UTCVendor advisory
  28. 2026-09-05 05:38 UTCVendor advisory
  29. 2026-09-04 17:52 UTCEG score recompute
  30. 2026-09-04 17:52 UTCVendor advisory
  31. 2026-09-04 06:05 UTCEG score recompute
  32. 2026-09-04 06:05 UTCVendor advisory
  33. 2026-09-04 05:07 UTCEPSS rescore
  34. 2026-09-03 13:16 UTCEG score recompute
  35. 2026-09-03 13:02 UTCEG score recompute
  36. 2026-09-02 16:38 UTCEG score recompute
  37. 2026-09-02 16:04 UTCEG score recompute
  38. 2026-09-02 15:27 UTCEG score recompute
  39. 2026-09-02 15:26 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-78409?
CVE-2026-78409 is a high vulnerability published on September 2, 2026. The X-mount.subdir option uses a detached-tree fast path on Linux 6.15 and later and passes the configured subdirectory to opentree() with ATSYMLINK_NOFOLLOW. That flag does not stop intermediate symlink traversal or keep resolution inside the newly mounted filesystem. A local unprivileged user…
When was CVE-2026-78409 disclosed?
CVE-2026-78409 was first published in the National Vulnerability Database on September 2, 2026, with the most recent update on September 3, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-78409 actively exploited?
CVE-2026-78409 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 97.5% of all scored CVEs.
What is the CVSS score of CVE-2026-78409?
CVE-2026-78409 has a CVSS v3 base score of 7.0 (NVD).
How do I remediate CVE-2026-78409?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-78409, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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