CVE-2025-40212: nfsd: fix refcount leak in nfsd_set_fh_dentry()
In the Linux kernel, the following vulnerability has been resolved:
nfsd: fix refcount leak in nfsdsetfhdentry()
nfsd exports a "pseudo root filesystem" which is used by NFSv4 to find the various exported filesystems using LOOKUP requests from a known root filehandle. NFSv3 uses the MOUNT protocol to find those exported filesystems and so is not given access to the pseudo root filesystem.
If a v3 (or v2) client uses a filehandle from that filesystem, nfsdsetfhdentry() will report an error, but still stores the export in "struct svcfh" even though it also drops the reference (expput()). This means that when fhput() is called an extra reference will be dropped which can lead to use-after-free and possible denial of service.
Normal NFS usage will not provide a pseudo-root filehandle to a v3 client. This bug can only be triggered by the client synthesising an incorrect filehandle.
To fix this we move the assignments to the svcfh later, after all possible error cases have been detected.
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2025-40212?
CVE-2025-40212 is classified as a medium severity vulnerability due to its potential impact on the Linux kernel's NFS server.
How do I fix CVE-2025-40212?
To fix CVE-2025-40212, update your Linux kernel to the latest version provided by your distribution that includes the security patches.
What systems are affected by CVE-2025-40212?
CVE-2025-40212 affects all versions of the Linux kernel that utilize the NFS server functionality.
What is the nature of the vulnerability in CVE-2025-40212?
CVE-2025-40212 involves a refcount leak in the nfsd_set_fh_dentry() function, which can lead to resource management issues.
Is there any known exploit for CVE-2025-40212?
As of now, there are no known public exploits for CVE-2025-40212, but it is advisable to apply the necessary patches as a precaution.