CVE-2023-53825: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-53825 is a memory management vulnerability in the Linux kernel's KCM (Kernel Connection Multiplexor) subsystem, specifically in the kcm_sendmsg() function. The flaw involves improper error handling for SOCK_DGRAM sockets, where a failed sendmsg() call could corrupt the MSG_MORE queue by resuming from an incorrect socket buffer (skb). The vulnerability was originally discovered by syzkaller (Google's kernel fuzzer) and was disclosed on December 9, 2025. It affects Linux kernel versions from 4.6 (when KCM was introduced) through multiple stable branches, with fixes backported to versions 4.14.326, 4.19.295, 5.4.257, 5.10.195, 5.15.132, 6.1.54, 6.5.4, and 6.6. The CVSS score has not been formally assigned, but Feedly estimates the severity as Medium (Feedly, EUVD).

The root cause is improper error handling (CWE-755: Improper Handling of Exceptional Conditions) in the kcm_sendmsg() function within the Linux kernel's KCM subsystem. A prior fix (commit c821a88bd720) attempted to address a memory leak by updating kcm_tx_msg(head)->last_skb when partial data is copied during an error, allowing subsequent sendmsg() calls to resume from that skb. However, because the exact number of bytes copied cannot be determined at error time, the MSG_MORE queue can become corrupted — subsequent sendmsg() calls resume from a wrong skb, leading to queue state inconsistency. The correct fix purges the pending queue on SOCK_DGRAM failure (analogous to udp_flush_pending_frames()), without affecting SOCK_SEQPACKET behavior. The vulnerability requires local access to a system with KCM sockets enabled (Feedly, EUVD).

Exploitation of this vulnerability can result in kernel memory queue corruption within the KCM subsystem, potentially leading to memory leaks or undefined behavior when the MSG_MORE queue is in an inconsistent state. The primary impact is on availability and integrity of kernel networking state for processes using KCM SOCK_DGRAM sockets. While the vulnerability was only triggered by syzkaller fuzzing and no real-world exploitation has been reported, a local attacker with access to KCM sockets could potentially leverage the corrupted queue state to cause a denial of service or, in a worst case, influence kernel memory layout (Feedly).

The Linux kernel has released patches across multiple stable branches: 4.14.326, 4.19.295, 5.4.257, 5.10.195, 5.15.132, 6.1.54, 6.5.4, and 6.6. Users should update their Linux kernel to one of these patched versions. The fix is available via the upstream stable kernel git repository across eight separate commits. As a workaround, systems that do not require KCM socket functionality can disable or restrict access to KCM sockets via kernel module controls or seccomp/LSM policies (EUVD, Feedly).

SUSE has issued advisories (SUSE-2026-0281-1 and SUSE-2026-20876-1) addressing this CVE as part of broader kernel update packages. Tenable has published Nessus detection plugins (278544 and 298924) for this vulnerability. No notable independent researcher commentary or significant social media discussion has been identified (LinuxSecurity, Tenable).