CVE-2025-40212: In the Linux kernel, the following vulnerability has been resolved: nfsd: fix refcount leak in nfsd_set_fh_dentry() nfsd exports a "pseudo root file...

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 been detected.

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

0.18%

7.8th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= ef7f6c4904d03ccd7478e1ac20ed75f79c4ac444, < b6bc86ce3944b10b9fc181fc00c1a520a20ed965; >= ef7f6c4904d03ccd7478e1ac20ed75f79c4ac444, < c83d7365cec5eb5ebeeee2a72e29b4ca58a7e4c2; >= ef7f6c4904d03ccd7478e1ac20ed75f79c4ac444, < 8a7348a9ed70bda1c1f51d3f1815bcbdf9f3b38c
Linux	Linux	6.12

References

Timeline

Published: Nov 24, 2025
Last Modified: Jul 30, 2026
Status: Deferred

Frequently Asked Questions

What is CVE-2025-40212?

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.

How severe is CVE-2025-40212?

CVE-2025-40212 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 0.18% probability of exploitation in the next 30 days.

How do I fix CVE-2025-40212?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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