CVE-2026-80634

CRITICALPre-NVD 9.89.8—
EchelonGraph scoreHIGH confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2026-08-28. a secondary CVSS source baseline 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 5 sources updated this week
9.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 9.8Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

In the Linux kernel, the following vulnerability has been resolved:

netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag

The DEV_PATH_BR_VLAN_UNTAG case post-decrements info->num_encaps inside WARN_ON_ONCE(). num_encaps is u8, so if it's already 0 the decrement still happens and wraps it to 255. The break only leaves the inner switch -- a later path entry can set info->indev back to a real device, and we end up returning with num_encaps == 255.

nft_dev_forward_path() then walks info.encap[] (size 2) up to num_encaps, which means an OOB stack read and a bogus count copied into the route descriptor.

Should only happen on a malformed bridge path stack, hence the WARN, but worth handling sanely. Move the decrement out of the WARN.

[ While at this, remove the WARN_ON_ONCE since this can only happen with a buggy bridge path stack --pablo ].

CVSS v3
9.8
EG Score
9.8(high)
EG Risk
49(Track)
EG Risk 49/100SSVC: 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
Severity98% × 45%
Exploitation0% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
31%
KEV
Not listed

Published

August 28, 2026

Last Modified

August 29, 2026

Advisory Details (2)

Auto-updated Aug 29, 2026
No patch confirmed yet.
generic

netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/e052f920773b73be49eb4d8702a9f85de7464363
generic

netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/2f55fa28011c97d6495d5787808db10a8c2d690d

Vendor Advisories for CVE-2026-80634(1)

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

Data Freshness Timeline

(refreshed 17× in last 7d / 17× 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. 2026-08-30 05:24 UTCEG score recompute
  2. 2026-08-30 05:24 UTCGHSA enrichment
  3. 2026-08-30 01:22 UTCEPSS rescore
  4. 2026-08-30 01:01 UTCGHSA enrichment
  5. 2026-08-29 20:39 UTCGHSA enrichment
  6. 2026-08-29 16:15 UTCGHSA enrichment
  7. 2026-08-29 11:51 UTCEG score recompute
  8. 2026-08-29 11:51 UTCGHSA enrichment
  9. 2026-08-29 07:27 UTCEG score recompute
  10. 2026-08-29 07:27 UTCGHSA enrichment
  11. 2026-08-29 06:37 UTCEG score recompute▲ 9.80
  12. 2026-08-29 06:36 UTCGHSA enrichment
  13. 2026-08-29 06:33 UTCMITRE cvelistV5CVSS v3 → 9.8 · severity → CRITICAL
  14. 2026-08-28 21:42 UTCEPSS rescore
  15. 2026-08-28 08:20 UTCNVD update
  16. 2026-08-28 07:34 UTCEG score recompute
  17. 2026-08-28 07:32 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-80634?
CVE-2026-80634 is a critical vulnerability published on August 28, 2026. In the Linux kernel, the following vulnerability has been resolved: netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag The DEVPATHBRVLANUNTAG case post-decrements info->num_encaps inside WARNONONCE(). num_encaps is u8, so if it's already 0 the decrement still happens and wraps it…
When was CVE-2026-80634 disclosed?
CVE-2026-80634 was first published in the National Vulnerability Database on August 28, 2026, with the most recent update on August 29, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-80634 actively exploited?
CVE-2026-80634 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 69.2% of all scored CVEs.
What is the CVSS score of CVE-2026-80634?
CVE-2026-80634 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2026-80634?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-80634, 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.

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