CVE-2025-40326 NFSD: Define actions for the new time_deleg FATTR4 attributes
A flaw in the Linux kernel's NFS server could cause a crash when handling invalid GETATTR requests for new time_deleg attributes.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40326?
CVE-2025-40326 is a high-severity denial of service vulnerability in Linux, published on 8 Dec 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: Define actions for the new time_deleg FATTR4 attributes
NFSv4 clients won't send legitimate GETATTR requests for these new attributes because they are intended to be used only with CB_GETATTR and SETATTR. But NFSD has to do something besides crashing if it ever sees a GETATTR request that queries these attributes.
RFC 8881 Section 18.7.3 states:
> The server MUST return a value for each attribute that the client > requests if the attribute is supported by the server for the > target file system. If the server does not support a particular > attribute on the target file system, then it MUST NOT return the > attribute value and MUST NOT set the attribute bit in the result > bitmap. The server MUST return an error if it supports an > attribute on the target but cannot obtain its value. In that case, > no attribute values will be returned.
Further, RFC 9754 Section 5 states:
> These new attributes are invalid to be used with GETATTR, VERIFY, > and NVERIFY, and they can only be used with CB_GETATTR and SETATTR > by a client holding an appropriate delegation.
Thus there does not appear to be a specific server response mandated by specification. Taking the guidance that querying these attributes via GETATTR is "invalid", NFSD will return nfserr_inval, failing the request entirely.
Which versions are affected by CVE-2025-40326?
How do I fix CVE-2025-40326?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-40326 being exploited?
There is no known exploitation of CVE-2025-40326 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40326, DEBIAN-CVE-2025-40326, GHSA-3c64-vv99-p2qr, UBUNTU-CVE-2025-40326.