# CVE-2025-38349: eventpoll: don't decrement ep refcount while still holding the ep mutex > A use-after-free vulnerability in the Linux kernel's eventpoll subsystem allows attackers to execute arbitrary code or escalate privileges. - **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 18 Jul 2025 - **Updated:** 3 Oct 2026 - **Also known as:** A-432751421, ASB-A-432751421, AZL-65544, BELL-CVE-2025-38349, DEBIAN-CVE-2025-38349, ECHO-e238-0710-b4cc, GHSA-c7h3-7f54-949m, ROOT-OS-DEBIAN-12-CVE-2025-38349, ROOT-OS-UBUNTU-2204-CVE-2025-38349, ROOT-OS-UBUNTU-2404-CVE-2025-38349, UBUNTU-CVE-2025-38349 ## What is CVE-2025-38349? CVE-2025-38349 is a high-severity use after free vulnerability in Linux kernel, published on 18 Jul 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: eventpoll: don't decrement ep refcount while still holding the ep mutex Jann Horn points out that epoll is decrementing the ep refcount and then doing a mutex_unlock(&ep->mtx); afterwards. That's very wrong, because it can lead to a use-after-free. That pattern is actually fine for the very last reference, because the code in question will delay the actual call to "ep_free(ep)" until after it has unlocked the mutex. But it's wrong for the much subtler "next to last" case when somebody *else* may also be dropping their reference and free the ep while we're still using the mutex. Note that this is true even if that other user is also using the same ep mutex: mutexes, unlike spinlocks, can not be used for object ownership, even if they guarantee mutual exclusion. A mutex "unlock" operation is not atomic, and as one user is still accessing the mutex as part of unlocking it, another user can come in and get the now released mutex and free the data structure while the first user is still cleaning up. See our mutex documentation in Documentation/locking/mutex-design.rst, in particular the section [1] about semantics: "mutex_unlock() may access the mutex structure even after it has internally released the lock already - so it's not safe for another context to acquire the mutex and assume that the mutex_unlock() context is not using the structure anymore" So if we drop our ep ref before the mutex unlock, but we weren't the last one, we may then unlock the mutex, another user comes in, drops _their_ reference and releases the 'ep' as it now has no users - all while the mutex_unlock() is still accessing it. Fix this by simply moving the ep refcount dropping to outside the mutex: the refcount itself is atomic, and doesn't need mutex protection (that's the whole _point_ of refcounts: unlike mutexes, they are inherently about object lifetimes). Weakness: CWE-416 (Use After Free) ## Which versions are affected by CVE-2025-38349? It affects 1 product. Products: Linux kernel. ## How do I fix CVE-2025-38349? Apply the vendor's patch. ## Is CVE-2025-38349 being exploited? There is no known exploitation of CVE-2025-38349 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-2025-38349 and fix it if it is affected. What it is: CVE-2025-38349 is a high-severity use after free vulnerability in Linux kernel, published on 18 Jul 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-2025-38349 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-2025-38349/ (Markdown: https://insights.sbomify.com/CVE-2025-38349/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38349 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38349 - OSV: https://osv.dev/vulnerability/CVE-2025-38349 --- From sbomify Insights: https://insights.sbomify.com/CVE-2025-38349/ Summaries are generated and may contain mistakes; the official description above is the record.