diff -ruN samba-3.5.3.a/source3/auth/auth_sam.c samba-3.5.3.b/source3/auth/auth_sam.c
--- samba-3.5.3.a/source3/auth/auth_sam.c	2010-05-17 13:51:23.000000000 +0200
+++ samba-3.5.3.b/source3/auth/auth_sam.c	2010-05-21 12:24:20.894735508 +0200
@@ -82,6 +82,9 @@
 		if (!user_sess_key->data) {
 			return NT_STATUS_NO_MEMORY;
 		}
+		if (!nt_pw) {
+			return NT_STATUS_WRONG_PASSWORD;
+		}
 		SMBsesskeygen_ntv1(nt_pw, user_sess_key->data);
 		return hash_password_check(mem_ctx, lp_lanman_auth(),
 					   client_lm_hash,