CVE-2026-31669
Linux Kernel use-after-free
- Published24 Apr 2026
Description
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.
CVSS 3.1 breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HAffected products
Remediation
- https://git.kernel.org/stable/c/15fa9ead4d5e6b6b9c794e84144146c917f2cb62
- https://git.kernel.org/stable/c/3fd6547f5b8ac99687be6d937a0321efda760597
- https://git.kernel.org/stable/c/9b55b253907e7431210483519c5ad711a37dafa1
- https://git.kernel.org/stable/c/b313e9037d98c13938740e5ebda7852929366dff
- https://git.kernel.org/stable/c/eb9c6aeb512f877cf397deb1e4526f646c70e4a7
- https://git.kernel.org/stable/c/f6e1f25fa5e733570f6d6fe37a4dfed2a0deba47
References
- https://cert-portal.siemens.com/productcert/html/ssa-019113.html
- https://cert-portal.siemens.com/productcert/html/ssa-082556.html
- https://git.kernel.org/stable/c/15fa9ead4d5e6b6b9c794e84144146c917f2cb62
- https://git.kernel.org/stable/c/3fd6547f5b8ac99687be6d937a0321efda760597
- https://git.kernel.org/stable/c/9b55b253907e7431210483519c5ad711a37dafa1
- https://git.kernel.org/stable/c/b313e9037d98c13938740e5ebda7852929366dff
- https://git.kernel.org/stable/c/eb9c6aeb512f877cf397deb1e4526f646c70e4a7
- https://git.kernel.org/stable/c/f6e1f25fa5e733570f6d6fe37a4dfed2a0deba47
- https://git.kernel.org/stable/c/fb1f54b7d16f393b8b65d328410f78b4beea8fcc
Related CVEs
Recent high-severity vulnerabilities sharing a weakness type.
Frequently asked
Is CVE-2026-31669 being actively exploited?
CVE-2026-31669 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.82%.
How severe is CVE-2026-31669?
CVE-2026-31669 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.82% probability of exploitation.
Which products are affected by CVE-2026-31669?
Affected products include Linux Kernel.
How do I fix CVE-2026-31669?
Upgrade affected software to a fixed version, for example Linux Kernel 5.15.203 or later, then confirm no affected versions remain in your inventory.
How Secuno handles this
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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.