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.