CVE-2023-53990: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-53990 is a missing synchronization vulnerability in the Linux kernel's SMB3/CIFS client subsystem. Specifically, the cifs_del_deferred_close function modifies the deferred close file list without first acquiring the required deferred_lock, creating a race condition in a critical section. The vulnerability affects Linux kernel versions from commit ca08d0eac020 up to the respective fix commits across multiple stable branches. It was published on December 24, 2025, by kernel.org. No CVSS score has been assigned by NVD at this time, and the record is not currently prioritized for NVD enrichment (Feedly).

The root cause is a missing lock (CWE classification not formally assigned by NVD) — specifically a concurrency/race condition where cifs_del_deferred_close accesses and modifies the deferred close file list without holding deferred_lock. This is a classic time-of-check/time-of-use (TOCTOU) style race condition in kernel code. The fix, applied across multiple stable branches (5.15.111, 6.1.28, 6.2.15, 6.3.2, and 6.4), ensures deferred_lock is acquired before invoking cifs_del_deferred_close. Exploitation would require local access to a system using SMB3/CIFS mounts and the ability to trigger concurrent file close operations (Feedly, kernel.org patch).

Exploitation of this race condition could lead to memory corruption or use-after-free conditions within the kernel's SMB3/CIFS deferred close file list, potentially resulting in a kernel panic (denial of service) or, in more severe scenarios, privilege escalation on the local system. The impact is limited to systems that have SMB3/CIFS shares mounted and are running affected kernel versions. There is no indication of remote exploitability or data exfiltration risk beyond the local system (Feedly).

The Linux kernel maintainers have released patches across multiple stable branches. Users should update to kernel versions that include the following fixes: 5.15.111 (commit 0f87e18203bd), 6.1.28 (commit ab9ddc87a905), 6.2.15 (commit 3aa9d065b068), 6.3.2 (commit cb36365dac25), and 6.4 (commit 32a046ccaeea). As a workaround where patching is not immediately possible, avoiding the use of SMB3/CIFS mounts with deferred close functionality on affected systems can reduce exposure. Administrators should apply the relevant distribution kernel updates as soon as they are available (Feedly, kernel.org patch).