---
id: CVE-2026-31669
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  mptcp: fix slab-use-after-free in __inet_lookup_established

  The ehash table lookups are lockless and rely on
  SLAB_TYPESAFE_BY_RCU to guarantee socket memory stability
  …
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  mptcp: fix slab-use-after-free in __inet_lookup_established

  The ehash table lookups are lockless and rely on
  SLAB_TYPESAFE_BY_RCU to guarantee socket memory stability
  …
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-416
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 5.12.1, < 5.15.203'
  - 'linux_kernel >= 5.16, < 6.1.169'
  - 'linux_kernel >= 6.2, < 6.6.135'
  - 'linux_kernel >= 6.7, < 6.12.82'
  - 'linux_kernel >= 6.13, < 6.18.23'
  - 'linux_kernel >= 6.19, < 6.19.13'
  - linux_kernel = 5.12
  - linux_kernel = 7.0
patched:
  - linux_kernel 6.19.13
published: '2026-04-24'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T02:19:15.713'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-31669'
references:
  - url: 'https://git.kernel.org/stable/c/15fa9ead4d5e6b6b9c794e84144146c917f2cb62'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/3fd6547f5b8ac99687be6d937a0321efda760597'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/9b55b253907e7431210483519c5ad711a37dafa1'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/b313e9037d98c13938740e5ebda7852929366dff'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/eb9c6aeb512f877cf397deb1e4526f646c70e4a7'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/f6e1f25fa5e733570f6d6fe37a4dfed2a0deba47'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/fb1f54b7d16f393b8b65d328410f78b4beea8fcc'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-019113.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-082556.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-457936.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
  - nvd
  - cve.org
epss: 0.00471
epssPercentile: 0.40585
ingestedAt: '2026-09-08T15:33:26.989Z'
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-10-16T15:12:01.538596Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

mptcp: fix slab-use-after-free in __inet_lookup_established

The ehash table lookups are lockless and rely on
SLAB_TYPESAFE_BY_RCU to guarantee socket memory stability
during RCU read-side critical sections. Both tcp_prot and
tcpv6_prot have their slab caches created with this flag
via proto_register().

However, MPTCP's mptcp_subflow_init() copies tcpv6_prot into
tcpv6_prot_override during inet_init() (fs_initcall, level 5),
before inet6_init() (module_init/device_initcall, level 6) has
called proto_register(&tcpv6_prot). At that point,
tcpv6_prot.slab is still NULL, so tcpv6_prot_override.slab
remains NULL permanently.

This causes MPTCP v6 subflow child sockets to be allocated via
kmalloc (falling into kmalloc-4k) instead of the TCPv6 slab
cache. The kmalloc-4k cache lacks SLAB_TYPESAFE_BY_RCU, so
when these sockets are freed without SOCK_RCU_FREE (which is
cleared for child sockets by design), the memory can be
immediately reused. Concurrent ehash lookups under
rcu_read_lock can then access freed memory, triggering a
slab-use-after-free in __inet_lookup_established.

Fix this by splitting the IPv6-specific initialization out of
mptcp_subflow_init() into a new mptcp_subflow_v6_init(), called
from mptcp_proto_v6_init() before protocol registration. This
ensures tcpv6_prot_override.slab correctly inherits the
SLAB_TYPESAFE_BY_RCU slab cache.

## Affected

- `linux_kernel >= 5.12.1, < 5.15.203`
- `linux_kernel >= 5.16, < 6.1.169`
- `linux_kernel >= 6.2, < 6.6.135`
- `linux_kernel >= 6.7, < 6.12.82`
- `linux_kernel >= 6.13, < 6.18.23`
- `linux_kernel >= 6.19, < 6.19.13`
- `linux_kernel = 5.12`
- `linux_kernel = 7.0`

## Remediation

Upgrade past the affected range:

- `linux_kernel 6.19.13`