CVE-2023-53836: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-53836 is a use-after-free vulnerability in the Linux kernel's BPF sockmap subsystem, specifically in the sk_psock_backlog handling after locking changes. The flaw arises from a race condition where socket buffers (sk_buff) from the backlog queue can be referenced after userspace has already consumed and freed them via consume_skb(). It affects the Linux kernel and was published on December 9, 2025. The CVSS category is estimated as Medium, with an EPSS score of 0.000180 (Feedly).

The root cause is a race condition (CWE-416: Use After Free) in the BPF sockmap ingress path. When sk_psock_handle_skb() processes an ingress SKB, it calls sk_psock_skb_ingress_enqueue(), which places the sk_buff pointer into a message (msg->skb) on the ingress_msg queue. A recvmsg() call from userspace can read and free the SKB via consume_skb() before the backlog loop completes its skb_dequeue() on psock->ingress_skb, resulting in a use-after-free. The !ingress path is not affected because it uses sendmsg_*() which does not propagate the sk_buff further. The bug was observed via a kernel splat during test_progs -t sockmap_listen (Feedly).

Successful exploitation of this race condition can lead to kernel memory corruption due to the use-after-free, potentially enabling local privilege escalation, kernel crash (denial of service), or arbitrary code execution in kernel context. The vulnerability affects systems using BPF sockmap with ingress traffic redirection, which is common in advanced networking and container/service mesh environments. Data confidentiality and system integrity may both be compromised if an attacker can reliably trigger and control the race (Feedly).

The Linux kernel maintainers have addressed this vulnerability through patches committed to stable kernel trees (commits 65ad600b9bde, 923877254f00, a454d84ee20b, and e6b5e47adb91 on kernel.org). Users should update to a patched kernel version as provided by their Linux distribution. Downstream vendors including Amazon Linux 2 (ALAS2KERNEL-5.15-2025-087) and SUSE have released updated kernel packages incorporating the fix (Amazon Linux Advisory, Linux Security SUSE). As a workaround where patching is not immediately possible, disabling BPF sockmap ingress redirection can mitigate exposure.