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.
- 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
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): [<ffffffffaa68fb49>] __kmalloc_noprof+0x359/0x510 [<ffffffffc32bf1df>] ceph_mds_check_access+0x5bf/0x14e0 [ceph] [<ffffffffc3235722>] ceph_open+0x312/0xd80 [ceph] [<ffffffffaa7dd786>] do_dentry_open+0x456/0x1120 [<ffffffffaa7e3729>] vfs_open+0x79/0x360 [<ffffffffaa832875>] path_openat+0x1de5/0x4390 [<ffffffffaa834fcc>] do_filp_open+0x19c/0x3c0 [<ffffffffaa7e44a1>] do_sys_openat2+0x141/0x180 [<ffffffffaa7e4945>] __x64_sys_open+0xe5/0x1a0 [<ffffffffac2cc2f7>] do_syscall_64+0xb7/0x210 [<ffffffffac400130>] 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=<hidden>,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
Which versions are affected by CVE-2025-21737?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-21737?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
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
Sources
Also known as BELL-CVE-2025-21737, DEBIAN-CVE-2025-21737, GHSA-755w-2h7x-xvj6, UBUNTU-CVE-2025-21737.