CVE-2025-40326

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.