CVE-2025-40212
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk32th percentile - higher than 32% of all known CVEs
Summary
In the Linux kernel, a refcount leak in nfsd_set_fh_dentry() occurs when an NFSv3 (or v2) client uses a pseudo-root filehandle. The export is stored in svc_fh but the reference is dropped, leading to a double free and potential use-after-free.
Risk Assessment
An attacker could trigger use-after-free, leading to denial of service (DoS) or potentially arbitrary code execution in kernel context.
Recommendation
Apply the Linux kernel patch that moves assignments to svc_fh after error checks to prevent the refcount leak.
Original NVD description (English source)
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 been detected.