CVE-2026-80585
Description
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".
How to fix
- Linux Linuxf75f174edc865738522e514d042cf5627f084859, fca7e444c04689fe4cc6b56f2725f804a4bb1ef9, 75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5, 72b4a0c51a4b550d40301d60a366b429b8c8e78d, e00b63056fb4f261455b3e5df5268a1f8ce47a87 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| Linux Linux | 36b122baf6a8bd46b4a591f12f4ed17b22257408 ≤ v < f75f174edc865738522e514d042cf5627f084859, 36b122baf6a8bd46b4a591f12f4ed17b22257408 ≤ v < fca7e444c04689fe4cc6b56f2725f804a4bb1ef9, 36b122baf6a8bd46b4a591f12f4ed17b22257408 ≤ v < 75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5, 36b122baf6a8bd46b4a591f12f4ed17b22257408 ≤ v < 72b4a0c51a4b550d40301d60a366b429b8c8e78d, 36b122baf6a8bd46b4a591f12f4ed17b22257408 ≤ v < e00b63056fb4f261455b3e5df5268a1f8ce47a87, 6.2 | f75f174edc865738522e514d042cf5627f084859, fca7e444c04689fe4cc6b56f2725f804a4bb1ef9, 75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5, 72b4a0c51a4b550d40301d60a366b429b8c8e78d, e00b63056fb4f261455b3e5df5268a1f8ce47a87 |
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