Answer in brief
CVE-2026-80585 records a Critical severity (CVSS 9.4) vulnerability in mptcp: fastopen: only mark MPTFO subflows with SYN data. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 9.4. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=36b122baf6a8bd46b4a591f12f4ed17b22257408 <f75f174edc865738522e514d042cf5627f084859 || >=36b122baf6a8bd46b4a591f12f4ed17b22257408 <fca7e444c04689fe4cc6b56f2725f804a4bb1ef9 || >=36b122baf6a8bd46b4a591f12f4ed17b22257408 <75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5 || >=36b122baf6a8bd46b4a591f12f4ed17b22257408 <72b4a0c51a4b550d40301d60a366b429b8c8e78d || >=36b122baf6a8bd46b4a591f12f4ed17b22257408 <e00b63056fb4f261455b3e5df5268a1f8ce47a87 | f75f174edc865738522e514d042cf5627f084859, fca7e444c04689fe4cc6b56f2725f804a4bb1ef9, 75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5, 72b4a0c51a4b550d40301d60a366b429b8c8e78d, e00b63056fb4f261455b3e5df5268a1f8ce47a87 |
| Linux/Linuxgeneric | 6.2 | Not reported |
Published upstream
Aug 26, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 27, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 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. 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".
Quoted source text, attributed separately from HOL analysis.