# CVE-2025-68214: timers: Fix NULL function pointer race in timer_shutdown_sync() > A race condition in the Linux kernel timer subsystem can cause a NULL function pointer dereference, leading to a system crash or denial of service. - **Severity:** Medium 4.7 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Local or same network only - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 16 Dec 2025 - **Updated:** 23 May 2026 - **Also known as:** ALSA-2026:49870, AZL-72475, BELL-CVE-2025-68214, DEBIAN-CVE-2025-68214, GHSA-q35m-cwfx-j6jx, RHSA-2026:49870, RLSA-2026:49870, ROOT-OS-DEBIAN-12-CVE-2025-68214, ROOT-OS-DEBIAN-13-CVE-2025-68214, ROOT-OS-UBUNTU-2204-CVE-2025-68214, ROOT-OS-UBUNTU-2404-CVE-2025-68214, RXSA-2026:49870, UBUNTU-CVE-2025-68214 ## What is CVE-2025-68214? CVE-2025-68214 is a medium-severity vulnerability in Linux kernel, published on 16 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim. ### Official description In the Linux kernel, the following vulnerability has been resolved: timers: Fix NULL function pointer race in timer_shutdown_sync() There is a race condition between timer_shutdown_sync() and timer expiration that can lead to hitting a WARN_ON in expire_timers(). The issue occurs when timer_shutdown_sync() clears the timer function to NULL while the timer is still running on another CPU. The race scenario looks like this: CPU0 CPU1 lock_timer_base() expire_timers() base->running_timer = timer; unlock_timer_base() [call_timer_fn enter] mod_timer() ... timer_shutdown_sync() lock_timer_base() // For now, will not detach the timer but only clear its function to NULL if (base->running_timer != timer) ret = detach_if_pending(timer, base, true); if (shutdown) timer->function = NULL; unlock_timer_base() [call_timer_fn exit] lock_timer_base() base->running_timer = NULL; unlock_timer_base() ... // Now timer is pending while its function set to NULL. // next timer trigger expire_timers() WARN_ON_ONCE(!fn) // hit ... lock_timer_base() // Now timer will detach if (base->running_timer != timer) ret = detach_if_pending(timer, base, true); if (shutdown) timer->function = NULL; unlock_timer_base() The problem is that timer_shutdown_sync() clears the timer function regardless of whether the timer is currently running. This can leave a pending timer with a NULL function pointer, which triggers the WARN_ON_ONCE(!fn) check in expire_timers(). Fix this by only clearing the timer function when actually detaching the timer. If the timer is running, leave the function pointer intact, which is safe because the timer will be properly detached when it finishes running. Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) ## Which versions are affected by CVE-2025-68214? It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `kernel` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-64k` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-64k-core` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-64k-debug` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-64k-debug-core` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-64k-debug-devel` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-64k-debug-devel-matched` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-64k-debug-modules` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-64k-debug-modules-core` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-64k-debug-modules-extra` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-64k-devel` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-64k-devel-matched` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-64k-modules` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-64k-modules-core` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-64k-modules-extra` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-abi-stablelists` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-core` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-cross-headers` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-debug` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-debug-core` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-debug-devel` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-debug-devel-matched` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-debug-modules` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-debug-modules-core` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-debug-modules-extra` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-debug-uki-virt` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-devel` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-devel-matched` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-doc` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-headers` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-modules` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-modules-core` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-modules-extra` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-rt` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-rt-64k` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-rt-64k-core` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-rt-64k-debug` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-rt-64k-debug-core` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-rt-64k-debug-devel` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | | `kernel-rt-64k-debug-modules` | AlmaLinux:9 | All versions | 5.14.0-687.34.1.el9_8 | Products: Linux kernel. ## How do I fix CVE-2025-68214? Apply the vendor's patch. ## Is CVE-2025-68214 being exploited? There is no known exploitation of CVE-2025-68214 in the wild and no public exploit code. ## Other vulnerabilities in Linux kernel - [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild) - [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild) - [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild) - [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild) - [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2025-68214 and fix it if it is affected. What it is: CVE-2025-68214 is a medium-severity vulnerability in Linux kernel, published on 16 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2025-68214 in the wild and no public exploit code. Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2025-68214/ (Markdown: https://insights.sbomify.com/CVE-2025-68214/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2025-68214 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-68214 - OSV: https://osv.dev/vulnerability/CVE-2025-68214 --- From sbomify Insights: https://insights.sbomify.com/CVE-2025-68214/ Summaries are generated and may contain mistakes; the official description above is the record.