CVE-2025-40212

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

nfsd: fix refcount leak in nfsd_set_fh_dentry()

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,

nfsd_set_fh_dentry() will report an error, but still stores the export

in "struct svc_fh" even though it also drops the reference (exp_put()).

This means that when fh_put() 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 svc_fh later, after all

possible error cases have b

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References