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VulnerabilityPublished Updated

CVE-2025-21707: Linux kernel · mptcp: consolidate suboption status

Affects Linux kernelSource GCVE Database

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Not known to be exploited · CVSS 9.8 Critical.

Data as of 10 Nov 2026, 14:04 UTC

CVSS 3.1 base score
9.8Critical
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (Linux)CVSS 3.19.8
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 27 Feb 2025

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 10 Nov 2026.

What to do

AI-suggested

A fix for this vulnerability has been implemented in the Linux kernel. Users and administrators should apply the official Linux kernel updates that address this issue to ensure the MPTCP suboption status bitfields are properly initialized. Since this is a kernel-level vulnerability, upgrading to the patched kernel version is the recommended mitigation.

Description

CVE-2025-21707 is a critical vulnerability in the Linux kernel's Multipath TCP (MPTCP) implementation. The flaw arises from improper initialization of bitfields that track received MPTCP suboptions, leading to uninitialized memory usage. This inconsistency was detected by syzbot triggering kernel memory sanitizer (KMSAN) bugs. The vulnerability could potentially allow attackers to cause memory corruption or kernel instability.

References

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