Don't assume argv[0] is set without first checking argc.

src/parse_args.c

@@ -379,8 +379,10 @@ parse_args(int argc, char **argv, int *nargc, char ***nargv,
     }
     env_add[nenv] = NULL;
 
+    if (argc > 0) {
 	argc -= optind;
 	argv += optind;
+    }
 
     if (!mode) {
 	/* Defer -k mode setting until we know whether it is a flag or not */

src/sudo.c

@@ -183,7 +183,7 @@ main(int argc, char *argv[], char *envp[])
 	NULL, NULL, sudo_conf_debug_files(getprogname()));
 
     /* Make sure we are setuid root. */
-    sudo_check_suid(argv[0]);
+    sudo_check_suid(argc > 0 ? argv[0] : "sudo");
 
     /* Reset signal mask, save signal state and make sure fds 0-2 are open. */
     (void) sigemptyset(&mask);