# netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag

CVE record · `CVE-2026-80634`

- **Identifiers:** `CVE-2026-80634`
- **State:** Confirmed
- **Severity:** CVSS 9.8 Critical
- **Critical:** Yes: CVSS 9+
- **CNA:** Linux
- **Technologies:** [Linux kernel](https://agentprime.io/advisories/technology/linux-kernel.md)
- **Published:** 28 Aug 2026
- **Updated:** 30 Oct 2026
- **Reviewed by a person:** No

Published by the CVE Program (CNA: Linux) at 28 Aug 2026, 06:48 UTC. agentprime has not analysed this yet, so whether it affects any app is not known. This CVE names a vendor and product rather than a package, so the lockfile check doesn’t match it.

## Critical

Critical, because:

- CVSS score 9.8: 9.0 or more.

How we decide what’s critical: <https://agentprime.io/advisories/critical.md>

## Affected products, as the CNA wrote them

- Vendor: Linux. Product: Linux.
  - affected: `e990cef6516daa4e1e236433579e333f74fd38cb to before 9a4e3a9017ba3da2de187b72ed6545641a0d0a84` (git)
  - affected: `e990cef6516daa4e1e236433579e333f74fd38cb to before 1b52aeb40c9f04bf50eeb4ea09142139d163e239` (git)
  - affected: `e990cef6516daa4e1e236433579e333f74fd38cb to before ee8440bb000fff4ef8acbfc99652851e9ca0a35b` (git)
  - affected: `e990cef6516daa4e1e236433579e333f74fd38cb to before 547ea9f567498e4accc89e7816264f15a1a0629f` (git)
  - affected: `e990cef6516daa4e1e236433579e333f74fd38cb to before 2f55fa28011c97d6495d5787808db10a8c2d690d` (git)
  - affected: `e990cef6516daa4e1e236433579e333f74fd38cb to before e052f920773b73be49eb4d8702a9f85de7464363` (git)
  - Other versions: unaffected
- Vendor: Linux. Product: Linux.
  - affected: `5.13`
  - unaffected: `before 5.13` (semver)
  - unaffected: `6.1.191 to 6.1.*, inclusive` (semver)
  - unaffected: `6.6.160 to 6.6.*, inclusive` (semver)
  - unaffected: `6.12.114 to 6.12.*, inclusive` (semver)
  - unaffected: `6.18.57 to 6.18.*, inclusive` (semver)
  - unaffected: `7.1.5 to 7.1.*, inclusive` (semver)
  - unaffected: `7.2 to *, inclusive` (original_commit_for_fix)
  - Other versions: affected

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> The Linux kernel netfilter flowtable code, from 5.13, can underflow a counter during bridge VLAN untagging when a bridge path stack is malformed, leading to an out-of-bounds stack read. The source gives few details on how an attacker would reach this. Upgrade to 6.1.191, 6.6.160, 6.12.114, 6.18.57, or a later fixed release in those series.

Written 12 Nov 2026.

## Not analysed yet

We haven’t published our own analysis of this CVE. If a person reviews it, this page will say what’s affected and what has to be true for it to matter.

## Severity and exploitation

- 9.8 Critical, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`, from CNA (Linux)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0060, the 49th percentile, on 15 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

This record came from the full history of the CVE Program, published 28 Aug 2026. New records show when each source confirmed them.

## Sources

- [CVE List: CVE-2026-80634](https://www.cve.org/CVERecord?id=CVE-2026-80634)
- [NVD: CVE-2026-80634](https://nvd.nist.gov/vuln/detail/CVE-2026-80634)

### References from the CNA

- <https://git.kernel.org/stable/c/9a4e3a9017ba3da2de187b72ed6545641a0d0a84>
- <https://git.kernel.org/stable/c/1b52aeb40c9f04bf50eeb4ea09142139d163e239>
- <https://git.kernel.org/stable/c/ee8440bb000fff4ef8acbfc99652851e9ca0a35b>
- <https://git.kernel.org/stable/c/547ea9f567498e4accc89e7816264f15a1a0629f>
- <https://git.kernel.org/stable/c/2f55fa28011c97d6495d5787808db10a8c2d690d>
- <https://git.kernel.org/stable/c/e052f920773b73be49eb4d8702a9f85de7464363>

Facts on this page come from the CVE List as the CNA published them, with CVSS from the sources named above, CISA KEV and FIRST EPSS. Vendors, products and versions are shown as the CNA wrote them. We don’t reproduce the CVE’s description.

## Check whether this affects you

This CVE names a vendor and product rather than a package, so the lockfile check doesn’t match it. Compare the affected versions above with what you run.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), `get_advisory` returns this record and `search_advisories` finds related ones. Setup: <https://agentprime.io/mcp.md>
- As JSON: <https://api.agentprime.io/v1/advisories/CVE-2026-80634>
- Everything that needs attention now: <https://agentprime.io/advisories/critical.md>

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The web page: <https://agentprime.io/advisories/CVE-2026-80634/>. Everything for agents: <https://agentprime.io/llms.txt>.