CVE-2026-80585mptcp: fastopen: only mark MPTFO subflows with SYN data
Updated under an hour ago ()
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No exploitation reported and no EPSS estimate yet.
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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
- 9.4 CRITICAL (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H
- Weakness (CWE)
- Not given
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Linux
- NVD analysis
- Received
- Record last updated
- Oct 16, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Linux Linux linux:linux (from the name) | from 36b122baf6a8bd46b4a591f12f4ed17b22257408 before f75f174edc865738522e514d042cf5627f084859; from 36b122baf6a8bd46b4a591f12f4ed17b22257408 before fca7e444c04689fe4cc6b56f2725f804a4bb1ef9; from 36b122baf6a8bd46b4a591f12f4ed17b22257408 before 75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5; from 36b122baf6a8bd46b4a591f12f4ed17b22257408 before 72b4a0c51a4b550d40301d60a366b429b8c8e78d; from 36b122baf6a8bd46b4a591f12f4ed17b22257408 before e00b63056fb4f261455b3e5df5268a1f8ce47a87 | CNA record |
References
- https://git.kernel.org/stable/c/f75f174edc865738522e514d042cf5627f084859
- https://git.kernel.org/stable/c/fca7e444c04689fe4cc6b56f2725f804a4bb1ef9
- https://git.kernel.org/stable/c/75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5
- https://git.kernel.org/stable/c/72b4a0c51a4b550d40301d60a366b429b8c8e78d
- https://git.kernel.org/stable/c/e00b63056fb4f261455b3e5df5268a1f8ce47a87
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.