CVE-2025-40212 nfsd: fix refcount leak in nfsd_set_fh_dentry()
A refcount leak in the Linux kernel NFS server allows a malicious client to trigger a use-after-free, potentially causing a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40212?
CVE-2025-40212 is a critical use after free vulnerability in Linux, published on 24 Nov 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2025-40212?
Linux distribution packages (4)
kernel-livepatch-SLE16_Update_2 SUSE:Linux Enterprise Server 16.0 | All versions | 2-160000.1.1 |
kernel-livepatch-SLE16_Update_2 SUSE:Linux Enterprise Server for SAP applications 16.0 | All versions | 2-160000.1.1 |
kernel-livepatch-SLE16-RT_Update_2 SUSE:Linux Micro 6.2 | All versions | 2-160000.1.1 |
kernel-livepatch-SLE16_Update_2 SUSE:Linux Micro 6.2 | All versions | 2-160000.1.1 |
How do I fix CVE-2025-40212?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2025-40212 being exploited?
There is no known exploitation of CVE-2025-40212 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40212, DEBIAN-CVE-2025-40212, GHSA-cjm8-jghh-jmq3, ROOT-OS-DEBIAN-13-CVE-2025-40212, SUSE-SU-2026:20148-1, SUSE-SU-2026:20163-1 and 2 more.