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VulnerabilityPublished Updated

CVE-2026-31669: Linux kernel · mptcp: fix slab-use-after-free in __inet_lookup_established

Affects Linux kernelSource CVE Database V5

0

Not known to be exploited · CVSS 9.8 Critical · fixed in fb1f54b7d16f393b8b65d328410f78b4beea8fcc : patch Linux kernel as a priority.

Data as of 26 Oct 2026, 17:30 UTC

CVSS 3.1 base score
9.8Critical
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.4% chance of exploitation in 30 days – higher than 40% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CISA SSVC
Exploitation
No evidence of active exploitation and no public proof of concept
Automatable
Attackers can reliably automate steps 1–4 of the kill chain
Technical impact
Total control over the software or total information disclosure

CISA SSVC assessment, 2026-10-16.

Patch
Available – fixed in fb1f54b7d16f393b8b65d328410f78b4beea8fcc, f6e1f25fa5e733570f6d6fe37a4dfed2a0deba47, eb9c6aeb512f877cf397deb1e4526f646c70e4a7 +4
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 24 Apr 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: 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 26 Oct 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ b19bc2945b40b9fd38e835700907ffe8534ef0de, < fb1f54b7d16f393b8b65d328410f78b4beea8fcc
Fixed in
  • fb1f54b7d16f393b8b65d328410f78b4beea8fcc
LinuxLinuxAffected
  • ≥ b19bc2945b40b9fd38e835700907ffe8534ef0de, < f6e1f25fa5e733570f6d6fe37a4dfed2a0deba47
Fixed in
  • f6e1f25fa5e733570f6d6fe37a4dfed2a0deba47
LinuxLinuxAffected
  • ≥ b19bc2945b40b9fd38e835700907ffe8534ef0de, < eb9c6aeb512f877cf397deb1e4526f646c70e4a7
Fixed in
  • eb9c6aeb512f877cf397deb1e4526f646c70e4a7
LinuxLinuxAffected
  • ≥ b19bc2945b40b9fd38e835700907ffe8534ef0de, < b313e9037d98c13938740e5ebda7852929366dff
Fixed in
  • b313e9037d98c13938740e5ebda7852929366dff
LinuxLinuxAffected
  • ≥ b19bc2945b40b9fd38e835700907ffe8534ef0de, < 15fa9ead4d5e6b6b9c794e84144146c917f2cb62
Fixed in
  • 15fa9ead4d5e6b6b9c794e84144146c917f2cb62
LinuxLinuxAffected
  • ≥ b19bc2945b40b9fd38e835700907ffe8534ef0de, < 9b55b253907e7431210483519c5ad711a37dafa1
Fixed in
  • 9b55b253907e7431210483519c5ad711a37dafa1

AI-suggested

A fix is available and has been applied in the Linux kernel source code as indicated by the listed fixed commit versions. Users and administrators should update their Linux kernel to a version that includes these fixes to remediate the vulnerability. No additional mitigation steps are indicated by the vendor advisory.

Description

CVE-2026-31669 is a critical use-after-free vulnerability in the Linux kernel's multipath TCP (MPTCP) implementation affecting version 5.12. It arises from improper initialization of the tcpv6_prot_override slab cache, causing IPv6 MPTCP subflow child sockets to be allocated without the SLAB_TYPESAFE_BY_RCU flag. This leads to potential memory reuse and concurrent access to freed memory during ehash lookups, resulting in a slab-use-after-free in __inet_lookup_established. The issue is fixed by properly initializing the slab cache before protocol registration.

References

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