CVE-2023-53815: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-53815 is a livelock vulnerability in the Linux kernel's POSIX timer subsystem, specifically within the itimer_delete() function. The flaw allows a task to enter a livelock condition when it preempts the task performing timer delivery, occurring on RT (real-time) kernels and on non-RT kernels with HAVE_POSIX_CPU_TIMERS_TASK_WORK enabled. Affected Linux kernel versions include those prior to 5.10.188, 5.15.121, 6.1.39, 6.3.13, 6.4.4, and 6.5. The CVE was published on December 9, 2025, and is estimated as Medium severity with a CVSS base score of 0.0 as reported by ENISA (score not yet fully assigned) (ENISA EUVD, Feedly).

The root cause is a concurrency control defect (CWE-667: Improper Locking) in itimer_delete(), which contains a retry loop for handling timers that expire concurrently. On non-RT kernels with HAVE_POSIX_CPU_TIMERS_TASK_WORK enabled, and on all RT kernels, the function used spin_unlock() instead of timer_wait_running(), which is the correct mechanism used by other retry loops in the POSIX timer code. This mismatch allows a task to livelock by continuously preempting the timer delivery task without making forward progress. The fix replaces the spin_unlock() call with timer_wait_running() to align with the rest of the posix timer subsystem (ENISA EUVD, kernel.org patch).

Successful triggering of this vulnerability results in a system livelock, causing a denial of service (DoS) condition where the affected task and potentially the system become unresponsive. The impact is primarily an availability concern — there is no evidence of confidentiality or integrity compromise. The issue is most severe on RT kernels used in latency-sensitive or real-time workloads, where livelock can cause complete task starvation (ENISA EUVD, Feedly).

There is no known public exploit code or evidence of in-the-wild exploitation for CVE-2023-53815. The EPSS score is approximately 0.024% (0.000240), indicating a very low probability of exploitation in the near term. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. Exploitation would require local access and the ability to trigger concurrent timer expiration under specific kernel configurations (RT kernel or HAVE_POSIX_CPU_TIMERS_TASK_WORK enabled) (Feedly, Tenable Nessus).

The Linux kernel maintainers have released patches addressing this vulnerability across multiple stable branches. Users should upgrade to the following fixed versions or later: 5.10.188, 5.15.121, 6.1.39, 6.3.13, 6.4.4, or 6.5. Downstream distributions such as SUSE have also released updated kernel packages incorporating this fix. No configuration-based workaround is available; patching is the recommended remediation (ENISA EUVD, Linux Security SUSE Advisory).