CVE-2026-31669 Linux CVE debrief

Who should care

Linux kernel users and administrators should be aware of this vulnerability, as it can lead to potential crashes or code execution. Users of Linux kernel versions 5.12.1 to 5.15.203, 5.16 to 6.1.169, 6.2 to 6.6.135, 6.7 to 6.12.82, 6.13 to 6.18.23, 6.19 to 6.19.13, and 7.0 rc1 to rc7 are affected.

Technical summary

The vulnerability is caused by the incorrect initialization of the tcpv6_prot_override slab cache in MPTCP's mptcp_subflow_init() function. This function is called before inet6_init(), which initializes the tcpv6_prot slab cache with the SLAB_TYPESAFE_BY_RCU flag. As a result, MPTCP v6 subflow child sockets are allocated via kmalloc, which lacks SLAB_TYPESAFE_BY_RCU. This leads to a slab-use-after-free vulnerability in __inet_lookup_established when concurrent ehash lookups access freed memory under rcu_read_lock.

Defensive priority

High

Recommended defensive actions

• Apply the official patches provided by the Linux kernel maintainers.
• Update Linux kernel to a version that includes the fix, such as 5.15.204, 6.1.170, 6.6.136, 6.12.83, 6.18.24, or 6.19.14.
• Use a supported Linux kernel version and keep it up-to-date.
• Monitor system logs for potential crashes or errors related to the Linux kernel.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.

Evidence notes

The CVE record was published on 2026-04-24T15:16:46.663Z and was last modified on 2026-07-14T13:18:47.573Z. The NVD entry is currently Modified. This slab-use-after-free vulnerability in the Linux kernel's __inet_lookup_established function arises from MPTCP's mptcp_subflow_init() function copying tcpv6_prot into tcpv6_prot_override before inet6_init() has called proto_register(&tcpv6_prot). As a result, MPTCP v6 subflow child sockets are allocated via kmalloc instead of the TCPv6 slab cache, leading to a slab-use-after-free when concurrent ehash lookups access freed memory under rcu_read_lock. Evidence is limited to public CVE and NVD records.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.