CVE-2026-63867
Linux MPTCP TOCTOU race may corrupt rcv_wnd and disrupt connections.
Is CVE-2026-63867 being exploited?
Not confirmed. CVE-2026-63867 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.59% probability of exploitation in the next 30 days.
How severe is CVE-2026-63867?
CVE-2026-63867 is rated High with a CVSS score of 8.2. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-63867?
Yes. A fix has been recorded for CVE-2026-63867. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-63867 affect?
CVE-2026-63867 affects Linux kernel (MPTCP-enabled builds), Servers/routers using MPTCP, Embedded/network appliances with Linux MPTCP. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-63867?
Apply kernel MPTCP patch or disable MPTCP until updated.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote attackers can provoke MPTCP ack sequencing race to confuse peers, causing connection disruption or DoS via incorrect receive-window handling.
Patch when possible
- affected>= fa3fe2b150316b294f2c662653501273ff25bba8 and < 301a33fd590c408a05c5df800e0cc1e6a8a2f8f8
- affected>= fa3fe2b150316b294f2c662653501273ff25bba8 and < 68364963e5baf03f16b4420292291f75c8f66497
- affected>= fa3fe2b150316b294f2c662653501273ff25bba8 and < 907ac6b1658e0277f979fcdfae2a753b495c1510
- affected>= fa3fe2b150316b294f2c662653501273ff25bba8 and < c4f4cf60797974873dbc8e100144682a6f2f861f
- affected>= fa3fe2b150316b294f2c662653501273ff25bba8 and < 3b8cbba7c0ed31189c89f90be247b8973ffa79ef
- affected>= fa3fe2b150316b294f2c662653501273ff25bba8 and < 8f4f0a157e8436a05bf8c3670b24dbc258911c43
- affected>= fa3fe2b150316b294f2c662653501273ff25bba8 and < 8ab24fdebc369c0dfb90f82c1650b1e66662bb45
- affected5.11
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.