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CVE-2026-31669

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

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.15.203, 6.1.169, 6.6.135, 6.12.82, 6.18.23, and 1 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: yes
  • Technical impact: total

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 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.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: yes · Technical impact: total

  3. Record last updated

Affected versions

  • Linux Linux

    From b19bc2945b40b9fd38e835700907ffe8534ef0de · fixed in f6e1f25fa5e733570f6d6fe37a4dfed2a0deba47; From b19bc2945b40b9fd38e835700907ffe8534ef0de · fixed in fb1f54b7d16f393b8b65d328410f78b4beea8fcc; From b19bc2945b40b9fd38e835700907ffe8534ef0de · fixed in 3fd6547f5b8ac99687be6d937a0321efda760597; From b19bc2945b40b9fd38e835700907ffe8534ef0de · fixed in eb9c6aeb512f877cf397deb1e4526f646c70e4a7; From b19bc2945b40b9fd38e835700907ffe8534ef0de · fixed in 15fa9ead4d5e6b6b9c794e84144146c917f2cb62; From b19bc2945b40b9fd38e835700907ffe8534ef0de · fixed in b313e9037d98c13938740e5ebda7852929366dff; From b19bc2945b40b9fd38e835700907ffe8534ef0de · fixed in 9b55b253907e7431210483519c5ad711a37dafa1

  • Linux Linux

    5.12

  • KernelLinux

    From 5.12.0 · fixed in 5.15.203; From 5.16.0 · fixed in 6.1.169; From 6.2.0 · fixed in 6.6.135; From 6.7.0 · fixed in 6.12.82; From 6.13.0 · fixed in 6.18.23; From 6.19.0 · fixed in 6.19.13

References 7

git.kernel.org