SECUFOCUSNOW
Home›CVE index›CVE-2026-80585
ReviewCritical

CVE-2026-80585

Linux

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 af...

CVSS
9.4
EPSS
-
- percentile
CISA KEV
Not listed
Published
2026.08.27
PRIORITY ASSESSMENT

Review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability-
Technical severityCVSS 9.4

Vulnerability overview

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 af...

Affected product and versions

Product
Linux
Affected versions
>= 36b122baf6a8bd46b4a591f12f4ed17b22257408 < f75f174edc865738522e514d042cf5627f084859, >= 36b122baf6a8bd46b4a591f12f4ed17b22257408 < fca7e444c04689fe4cc6b56f2725f804a4bb1ef9, >= 36b122baf6a8bd46b4a591f12f4ed17b22257408 < 75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5, >= 36b122baf6a8bd46b4a591f12f4ed17b22257408 < 72b4a0c51a4b550d40301d60a366b429b8c8e78d, >= 36b122baf6a8bd46b4a591f12f4ed17b22257408 < e00b63056fb4f261455b3e5df5268a1f8ce47a87, >= 6.2
Fixed versions
No verified fixed-version field is available yet

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that Linux and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H
CWE
Not available