Bug 2461503 (CVE-2026-31669)

Summary:	CVE-2026-31669 kernel: mptcp: fix slab-use-after-free in __inet_lookup_established
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	rhel-process-autobot, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Linux kernel's Multipath TCP (MPTCP) implementation. Due to incorrect memory allocation for IPv6 subflow child sockets, a use-after-free vulnerability exists. A remote attacker could exploit this by triggering concurrent lookups in the kernel's hash table, potentially leading to a denial of service or arbitrary code execution.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-04-24 15:05:20 UTC

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.

Comment 1 Keith Grant 2026-04-24 22:36:33 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026042406-CVE-2026-31669-0e0d@gregkh/T

Comment 5 errata-xmlrpc 2026-06-16 18:29:36 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2026:26428 https://access.redhat.com/errata/RHSA-2026:26428

Comment 6 errata-xmlrpc 2026-06-16 18:55:31 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2026:26427 https://access.redhat.com/errata/RHSA-2026:26427

Comment 7 errata-xmlrpc 2026-06-19 23:21:52 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 10

Via RHSA-2026:27288 https://access.redhat.com/errata/RHSA-2026:27288

Comment 8 errata-xmlrpc 2026-06-22 05:01:31 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions

Via RHSA-2026:27713 https://access.redhat.com/errata/RHSA-2026:27713

Comment 9 errata-xmlrpc 2026-06-22 08:28:39 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9

Via RHSA-2026:27789 https://access.redhat.com/errata/RHSA-2026:27789

Comment 10 errata-xmlrpc 2026-06-29 19:23:52 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 10.0 Extended Update Support

Via RHSA-2026:33215 https://access.redhat.com/errata/RHSA-2026:33215

Comment 11 errata-xmlrpc 2026-07-01 00:13:33 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions

Via RHSA-2026:33900 https://access.redhat.com/errata/RHSA-2026:33900

Comment 12 errata-xmlrpc 2026-07-01 08:40:54 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions

Via RHSA-2026:34095 https://access.redhat.com/errata/RHSA-2026:34095

Comment 13 errata-xmlrpc 2026-07-01 08:59:01 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9.6 Extended Update Support

Via RHSA-2026:34094 https://access.redhat.com/errata/RHSA-2026:34094

Comment 14 errata-xmlrpc 2026-07-06 04:51:26 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions
  Red Hat Enterprise Linux 8.8 Telecommunications Update Service

Via RHSA-2026:35863 https://access.redhat.com/errata/RHSA-2026:35863

Comment 15 errata-xmlrpc 2026-07-06 13:42:06 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support
  Red Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-On

Via RHSA-2026:35894 https://access.redhat.com/errata/RHSA-2026:35894

Comment 16 errata-xmlrpc 2026-07-06 14:26:44 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support
  Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On

Via RHSA-2026:35896 https://access.redhat.com/errata/RHSA-2026:35896