# mptcp: fix uninitialized local_id in syncookie MP_JOIN reconstruction

CVE record · `CVE-2026-89554`

- **Identifiers:** `CVE-2026-89554`
- **State:** Confirmed
- **Severity:** CVSS 8.2 High
- **Critical:** No
- **CNA:** Linux
- **Technologies:** [Linux kernel](https://agentprime.io/advisories/technology/linux-kernel.md)
- **Published:** 11 Sept 2026
- **Updated:** 19 Oct 2026
- **Reviewed by a person:** No

Published by the CVE Program (CNA: Linux) at 11 Sept 2026, 19:44 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.

## Affected products, as the CNA wrote them

- Vendor: Linux. Product: Linux.
  - affected: `9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 4534e0eead692bb069ad1e6a5a245fc2e2078300` (git)
  - affected: `9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 63cacb05e51a1c6e1349d2e593d00fd6ef43def4` (git)
  - affected: `9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 954b5ea836eb118d188975ced803448537ab8479` (git)
  - affected: `9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 9df36a4846375a9b75bf42d77bfed216b0f366f9` (git)
  - affected: `9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 64f2c5dd49b956a542c8c02b8dad5d262a462bba` (git)
  - affected: `9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before 51887ccd88791ddaa8755a7c614fda031ecf7982` (git)
  - affected: `9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before bf19d166337c6488b39cb03eeeffb30a941d6326` (git)
  - affected: `9466a1ccebbe54ac57fb8a89c2b4b854826546a8 to before b878dfdd12d7a5b8722a78d35e313506140ca3d9` (git)
  - Other versions: unaffected
- Vendor: Linux. Product: Linux.
  - affected: `5.9`
  - unaffected: `before 5.9` (semver)
  - unaffected: `5.10.270 to 5.10.*, inclusive` (semver)
  - unaffected: `5.15.221 to 5.15.*, inclusive` (semver)
  - unaffected: `6.1.188 to 6.1.*, inclusive` (semver)
  - unaffected: `6.6.157 to 6.6.*, inclusive` (semver)
  - unaffected: `6.12.109 to 6.12.*, inclusive` (semver)
  - unaffected: `6.18.50 to 6.18.*, inclusive` (semver)
  - unaffected: `7.2.4 to 7.2.*, inclusive` (semver)
  - unaffected: `7.3 to *, inclusive` (original_commit_for_fix)
  - Other versions: affected

## 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

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

- **CISA KEV:** Not listed.
- **EPSS:** 0.0060, the 49th percentile, on 14 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 11 Sept 2026. New records show when each source confirmed them.

## Sources

- [CVE List: CVE-2026-89554](https://www.cve.org/CVERecord?id=CVE-2026-89554)
- [NVD: CVE-2026-89554](https://nvd.nist.gov/vuln/detail/CVE-2026-89554)

### References from the CNA

- <https://git.kernel.org/stable/c/4534e0eead692bb069ad1e6a5a245fc2e2078300>
- <https://git.kernel.org/stable/c/63cacb05e51a1c6e1349d2e593d00fd6ef43def4>
- <https://git.kernel.org/stable/c/954b5ea836eb118d188975ced803448537ab8479>
- <https://git.kernel.org/stable/c/9df36a4846375a9b75bf42d77bfed216b0f366f9>
- <https://git.kernel.org/stable/c/64f2c5dd49b956a542c8c02b8dad5d262a462bba>
- <https://git.kernel.org/stable/c/51887ccd88791ddaa8755a7c614fda031ecf7982>
- <https://git.kernel.org/stable/c/bf19d166337c6488b39cb03eeeffb30a941d6326>
- <https://git.kernel.org/stable/c/b878dfdd12d7a5b8722a78d35e313506140ca3d9>

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-2026-89554>
- Everything that needs attention now: <https://agentprime.io/advisories/critical.md>

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The web page: <https://agentprime.io/advisories/CVE-2026-89554/>. Everything for agents: <https://agentprime.io/llms.txt>.