--- a/sysdeps/mach/hurd/sendmsg.c
+++ b/sysdeps/mach/hurd/sendmsg.c
@@ -193,6 +193,49 @@
       goto label;
     }
 
+  /* Special case: message->msg_controllen <  sizeof (struct cmsghdr) */
+  /* Special case: cmsg == NULL and zero credentials byte sent */
+  else if (cmsg == NULL && (strncmp(data.ptr, "\0", 1) == 0))
+    {
+      union {
+	struct cmsghdr cmh;
+	char control[CMSG_SPACE(sizeof(struct cmsgcred))];
+	/* Space large enough to hold a cmsgcred structure */
+      } control_un;
+
+      struct msghdr msgh;
+      msgh.msg_name = NULL;
+      msgh.msg_namelen = 0;
+      msgh.msg_control = control_un.control;
+      msgh.msg_controllen = sizeof(control_un.control);
+      msgh.msg_flags = 0;
+
+      struct cmsghdr *cmhp = CMSG_FIRSTHDR(&msgh);
+      cmhp->cmsg_level = SOL_SOCKET;
+      cmhp->cmsg_type = SCM_CREDS;
+      cmhp->cmsg_len = CMSG_LEN(sizeof(struct cmsgcred));
+
+      ucredp = (struct cmsgcred *) CMSG_DATA(cmhp);
+      /* FIXME: to remove pid: not checked in check_auth? */
+      pid = __getpid();
+      euids = __geteuid();
+      auids = __getuid();
+      egids = __getegid();
+      agids = __getgid();
+      euidslen = auidslen = egidslen = agidslen = 1;
+
+      nports = 0;
+      control = control_un.control;
+      control_len = sizeof(control_un.control);
+
+      err = check_auth(euids, euidslen, auids, auidslen,
+			egids, egidslen, agids, agidslen,
+			ucredp);
+      if (err)
+	return __hurd_fail (err);
+      goto label;
+    }
+
   /* SCM_RIGHTS support: get the number of fds to send.  */
   cmsg = CMSG_FIRSTHDR (message);
   for (; cmsg; cmsg = CMSG_NXTHDR (message, cmsg))