CVE-2026-80585

CRITICALPre-NVD 9.49.4—
EchelonGraph scoreHIGH confidence

Score 9.4 from GitHub Security Advisory (severity: CRITICAL) published 2026-08-27. a secondary CVSS source baseline 9.4; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 5 sources updated this week
9.4EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 9.4Exploit: 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:

mptcp: fastopen: only mark MPTFO subflows with SYN data

Passive TCP Fast Open accepts a valid-cookie SYN even when it carries no data. In that case the child socket's receive queue is intentionally left empty.

mptcp_fastopen_subflow_synack_set_params() set is_mptfo before checking for queued SYN data. That made data-less TFO SYNs hit a WARN and, if the warning was non-fatal, left stale MPTFO state behind. The stale flag could later trigger a state-confusion bug in check_fully_established().

Only mark the subflow as MPTFO after confirming that an SKB was queued. Return quietly when the receive queue is empty.

Note that mptcp_subflow_context's is_mptfo field is now not just about subflows where the TFO was present, but about MPTFO subflow that consumed SYN data. Only having a valid cookie but not carrying data is not really "doing TFO".

CVSS v3
9.4
EG Score
9.4(high)
EG Risk
47(Track)
EG Risk 47/100SSVC: 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
Severity94% × 45%
Exploitation0% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
24%
KEV
Not listed

Published

August 26, 2026

Last Modified

August 27, 2026

Advisory Details (5)

Auto-updated Aug 27, 2026
No patch confirmed yet.
generic

mptcp: fastopen: only mark MPTFO subflows with SYN data - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/e00b63056fb4f261455b3e5df5268a1f8ce47a87
generic

mptcp: fastopen: only mark MPTFO subflows with SYN data - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/72b4a0c51a4b550d40301d60a366b429b8c8e78d
generic

mptcp: fastopen: only mark MPTFO subflows with SYN data - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5
generic

mptcp: fastopen: only mark MPTFO subflows with SYN data - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/fca7e444c04689fe4cc6b56f2725f804a4bb1ef9
generic

mptcp: fastopen: only mark MPTFO subflows with SYN data - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/f75f174edc865738522e514d042cf5627f084859

Vendor Advisories for CVE-2026-80585(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 29× in last 7d / 29× 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 03:31 UTCEG score recompute
  2. 2026-08-30 03:31 UTCGHSA enrichment
  3. 2026-08-30 01:22 UTCEPSS rescore
  4. 2026-08-29 23:36 UTCGHSA enrichment
  5. 2026-08-29 19:41 UTCGHSA enrichment
  6. 2026-08-29 15:46 UTCGHSA enrichment
  7. 2026-08-29 11:51 UTCGHSA enrichment
  8. 2026-08-29 07:51 UTCGHSA enrichment
  9. 2026-08-29 03:55 UTCGHSA enrichment
  10. 2026-08-28 23:57 UTCEG score recompute
  11. 2026-08-28 23:57 UTCGHSA enrichment
  12. 2026-08-28 21:42 UTCEPSS rescore
  13. 2026-08-28 17:44 UTCGHSA enrichment
  14. 2026-08-28 13:42 UTCGHSA enrichment
  15. 2026-08-28 09:46 UTCGHSA enrichment
  16. 2026-08-28 05:49 UTCGHSA enrichment
  17. 2026-08-28 01:53 UTCGHSA enrichment
  18. 2026-08-27 21:59 UTCGHSA enrichment
  19. 2026-08-27 18:04 UTCEG score recompute
  20. 2026-08-27 18:04 UTCGHSA enrichment
  21. 2026-08-27 14:25 UTCEPSS rescore
  22. 2026-08-27 14:08 UTCGHSA enrichment
  23. 2026-08-27 10:13 UTCEG score recompute
  24. 2026-08-27 10:13 UTCGHSA enrichment
  25. 2026-08-27 06:18 UTCEG score recompute▲ 9.40
Show 4 more
  1. 2026-08-27 06:11 UTCMITRE cvelistV5CVSS v3 → 9.4 · severity → CRITICAL
  2. 2026-08-26 15:43 UTCNVD update
  3. 2026-08-26 14:42 UTCEG score recompute
  4. 2026-08-26 14:41 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-80585?
CVE-2026-80585 is a critical vulnerability published on August 26, 2026. In the Linux kernel, the following vulnerability has been resolved: mptcp: fastopen: only mark MPTFO subflows with SYN data Passive TCP Fast Open accepts a valid-cookie SYN even when it carries no data. In that case the child socket's receive queue is intentionally left empty.…
When was CVE-2026-80585 disclosed?
CVE-2026-80585 was first published in the National Vulnerability Database on August 26, 2026, with the most recent update on August 27, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-80585 actively exploited?
CVE-2026-80585 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 76.0% of all scored CVEs.
What is the CVSS score of CVE-2026-80585?
CVE-2026-80585 has a CVSS v3 base score of 9.4 (NVD).
How do I remediate CVE-2026-80585?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-80585, 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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