CVE-2026-89554Medium· 5.5▾ SunlitA flaw was found in the Linux kernel's Multipath TCP (MPTCP) implementation. When reconstructing a Multipath TCP (MPTCP) join request under SYN cookies, the `local_id` field is not properly initialized. An off-path attacker can influence t…
▾ Sunlit zone — Low / medium · no exploitation signal
impact 30.3 · likelihood 0.1 · exploitation 0
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Exploit-prediction probability, daily snapshots since Sep 12.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via CSAF
0.2%
— → 6.5
none → medium
— → 6.5
none → medium
— → 8.2
none → high
8.2 → 6.5
high → medium
6.5 → 8.2
medium → high
Last analysed / modified upstream
0.2% → 0.6%
8.2 → 5.5
high → medium
A flaw was found in the Linux kernel's Multipath TCP (MPTCP) implementation. When reconstructing a Multipath TCP (MPTCP) join request under SYN cookies, the local_id field is not properly initialized. An off-path attacker can influence this uninitialized field by sending concurrent MP_JOIN SYN requests, leading to corruption of the path manager's subflow bookkeeping. This can result in a denial of service for affected MPTCP connections.
kernel: mptcp: fix uninitialized local_id in syncookie MP_JOIN reconstruction — rated Moderate by Red Hat. Released 2026-09-11, updated 2026-09-15.
Affected:
No fix planned:
Not affected:
Fix deferred
Field changes observed since this record was first indexed.
Connected by shared product, vendor, weakness, or advisory.
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