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

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Summary

CVECVE-2026-31669
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-24 15:16:46 UTC
Updated2026-04-27 20:09:25 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 9.8 CRITICAL from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS: 0.000300000 probability, percentile 0.086120000 (date 2026-04-27)

Problem Types: CWE-416

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected b19bc2945b40b9fd38e835700907ffe8534ef0de f6e1f25fa5e733570f6d6fe37a4dfed2a0deba47 git Not specified
CNA Linux Linux affected b19bc2945b40b9fd38e835700907ffe8534ef0de fb1f54b7d16f393b8b65d328410f78b4beea8fcc git Not specified
CNA Linux Linux affected b19bc2945b40b9fd38e835700907ffe8534ef0de 3fd6547f5b8ac99687be6d937a0321efda760597 git Not specified
CNA Linux Linux affected b19bc2945b40b9fd38e835700907ffe8534ef0de eb9c6aeb512f877cf397deb1e4526f646c70e4a7 git Not specified
CNA Linux Linux affected b19bc2945b40b9fd38e835700907ffe8534ef0de 15fa9ead4d5e6b6b9c794e84144146c917f2cb62 git Not specified
CNA Linux Linux affected b19bc2945b40b9fd38e835700907ffe8534ef0de b313e9037d98c13938740e5ebda7852929366dff git Not specified
CNA Linux Linux affected b19bc2945b40b9fd38e835700907ffe8534ef0de 9b55b253907e7431210483519c5ad711a37dafa1 git Not specified
CNA Linux Linux affected 5.12 Not specified
CNA Linux Linux unaffected 5.12 semver Not specified
CNA Linux Linux unaffected 5.15.203 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.169 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.135 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.82 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.23 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.13 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/fb1f54b7d16f393b8b65d328410f78b4beea8fcc 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/3fd6547f5b8ac99687be6d937a0321efda760597 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/f6e1f25fa5e733570f6d6fe37a4dfed2a0deba47 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/15fa9ead4d5e6b6b9c794e84144146c917f2cb62 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/9b55b253907e7431210483519c5ad711a37dafa1 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/eb9c6aeb512f877cf397deb1e4526f646c70e4a7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/b313e9037d98c13938740e5ebda7852929366dff 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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