CVE-2023-53831: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-53831 is a race condition vulnerability in the Linux kernel's networking subsystem, specifically in the sk_mc_loop() function in net/core/sock.c. The flaw arises because the function reads the sk->sk_family field multiple times without synchronization, which can lead to a WARN_ON_ONCE(1) kernel warning when the socket family is changed concurrently via IPV6_ADDRFORM. It affects the Linux kernel and was published on December 9, 2025. The CVSS category is estimated as Medium, with an EPSS score of 0.000240 (Feedly).

The root cause is a time-of-check/time-of-use (TOCTOU) race condition (CWE-362) in the sk_mc_loop() function (net/core/sock.c:782). The function reads sk->sk_family more than once without holding an appropriate lock, and if another thread concurrently changes the socket family using the IPV6_ADDRFORM socket option, the function may observe an inconsistent state and trigger a WARN_ON_ONCE(1). The fix involves reading sk->sk_family exactly once into a local variable to ensure a consistent view throughout the function's execution. The issue was surfaced by the syzbot fuzzer (Feedly).

Successful triggering of this vulnerability results in a kernel warning (WARN_ON_ONCE) in the networking stack, which can cause system instability or denial of service on affected Linux systems. The impact is primarily an availability concern — an attacker or local user with the ability to manipulate socket options (e.g., IPV6_ADDRFORM) concurrently with multicast operations could destabilize the kernel. There is no evidence of confidentiality or integrity impact beyond the kernel warning and potential system instability (Feedly).

The fix is to read sk->sk_family only once in sk_mc_loop() and store it in a local variable, preventing the TOCTOU race. Patches have been committed to the Linux kernel stable tree across multiple stable branches (commits 41f10a4d78fe, 895dc4c47171, 7586a66b9c4f, 9036b6342fcd, a3e0fdf71bbe). Users should update to a patched kernel version; SUSE has issued advisories (SUSE-2026-0281-1, SUSE-2026-20876-1) incorporating the fix. Administrators should apply the latest kernel updates from their Linux distribution vendor (Feedly, Linux Security).