# CVE-2025-21737: ceph: fix memory leak in ceph_mds_auth_match() > A memory leak in the Linux kernel CephFS module allows attackers to cause a system crash via kernel OOM by accessing files with path-scoped capabilities. - **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/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:** 27 Feb 2025 - **Updated:** 11 May 2026 - **Also known as:** BELL-CVE-2025-21737, DEBIAN-CVE-2025-21737, GHSA-755w-2h7x-xvj6, UBUNTU-CVE-2025-21737 ## What is CVE-2025-21737? CVE-2025-21737 is a medium-severity denial of service vulnerability in Linux kernel, published on 27 Feb 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: ceph: fix memory leak in ceph_mds_auth_match() We now free the temporary target path substring allocation on every possible branch, instead of omitting the default branch. In some cases, a memory leak occured, which could rapidly crash the system (depending on how many file accesses were attempted). This was detected in production because it caused a continuous memory growth, eventually triggering kernel OOM and completely hard-locking the kernel. Relevant kmemleak stacktrace: unreferenced object 0xffff888131e69900 (size 128): comm "git", pid 66104, jiffies 4295435999 hex dump (first 32 bytes): 76 6f 6c 75 6d 65 73 2f 63 6f 6e 74 61 69 6e 65 volumes/containe 72 73 2f 67 69 74 65 61 2f 67 69 74 65 61 2f 67 rs/gitea/gitea/g backtrace (crc 2f3bb450): [] __kmalloc_noprof+0x359/0x510 [] ceph_mds_check_access+0x5bf/0x14e0 [ceph] [] ceph_open+0x312/0xd80 [ceph] [] do_dentry_open+0x456/0x1120 [] vfs_open+0x79/0x360 [] path_openat+0x1de5/0x4390 [] do_filp_open+0x19c/0x3c0 [] do_sys_openat2+0x141/0x180 [] __x64_sys_open+0xe5/0x1a0 [] do_syscall_64+0xb7/0x210 [] entry_SYSCALL_64_after_hwframe+0x77/0x7f It can be triggered by mouting a subdirectory of a CephFS filesystem, and then trying to access files on this subdirectory with an auth token using a path-scoped capability: $ ceph auth get client.services [client.services] key = REDACTED caps mds = "allow rw fsname=cephfs path=/volumes/" caps mon = "allow r fsname=cephfs" caps osd = "allow rw tag cephfs data=cephfs" $ cat /proc/self/mounts services@[REDACTED].cephfs=/volumes/containers /ceph/containers ceph rw,noatime,name=services,secret=,ms_mode=prefer-crc,mount_timeout=300,acl,mon_addr=[REDACTED]:3300,recover_session=clean 0 0 $ seq 1 1000000 | xargs -P32 --replace={} touch /ceph/containers/file-{} && \ seq 1 1000000 | xargs -P32 --replace={} cat /ceph/containers/file-{} [ idryomov: combine if statements, rename rc to path_matched and make it a bool, formatting ] Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime) ## Which versions are affected by CVE-2025-21737? It affects 1 product. Products: Linux kernel. ## How do I fix CVE-2025-21737? Apply the vendor's patch. ## Is CVE-2025-21737 being exploited? There is no known exploitation of CVE-2025-21737 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-2025-21737 and fix it if it is affected. What it is: CVE-2025-21737 is a medium-severity denial of service vulnerability in Linux kernel, published on 27 Feb 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-2025-21737 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-2025-21737/ (Markdown: https://insights.sbomify.com/CVE-2025-21737/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21737 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21737 - OSV: https://osv.dev/vulnerability/CVE-2025-21737 --- From sbomify Insights: https://insights.sbomify.com/CVE-2025-21737/ Summaries are generated and may contain mistakes; the official description above is the record.