FreeBSD Security Advisory: FreeBSD-SA-98:03.ttcp

FreeBSD Security Officer security-officer at FreeBSD.ORG
Thu May 14 12:58:20 PDT 1998


FreeBSD-SA-98:03                                            Security Advisory
                                                                FreeBSD, Inc.

Topic:          Problems with TTCP

Category:       core
Module:         kernel
Announced:      1998-05-14
Affects:        FreeBSD 2.1.*
		FreeBSD 2.2.*,
		FreeBSD-stable before 1998/05/14 and
		FreeBSD-current before 1998/05/05 suffer from this problem.
Corrected:      FreeBSD-3.0-current as of 1998/05/14
		FreeBSD-2.2-stable as of 1998/05/05
FreeBSD only:   No. Any other system incorporating TTCP extentions may be


I.   Background    

     RFC 1644 provides an extension to TCP called TCP Extensions for
     Transactions, or shortly T/TCP. It provides a way of bypassing
     the standard three-way handshake found in TCP, thus speeding up
     T/TCP has been incorporated in FreeBSD since FreeBSD 2.0.5.

II.  Problem Description

     An accelerated open is initiated by a client by sending a new
     TCP option, called CC, to the server.  The kernel keeps a
     special cache for each host it communicated with, among others
     containing the value of the last CC option used by the client.
     A new accelerated open is allowed when the CC sent is larger
     than the one in the per-host cache. Thus one can spoof complete
III. Impact
     The hole can be used to obtain unauthorized acces to the system
     by spoofing connections to the r*-services. This can only be
     done in the case where an .rhost file and/or a host.equiv file
     is used as the sole method of authentication.

IV.  Workaround

     Disable all r-* services. Note that setting the kernel variable
     net.inet.tcp.rfc1644 to 0 does not solve the problem. This
     variable controls whether the system will initiate rfc1644
     based connections and does not affect the ability to receive
     such connections.

V.   Solution

     Apply the following patch, rebuild your kernel, install it
     and reboot your system. the patch is valid for 2.2.* as well as
     2.2-stable and 3.0-current systems.

     The patch below can be found on

  Index: tcp_input.c
  RCS file: /home/cvsup/freebsd/CVS/src/sys/netinet/tcp_input.c,v
  retrieving revision 1.74
  retrieving revision 1.75
  diff -u -r1.74 -r1.75
  --- tcp_input.c	1998/04/24 10:08:57	1.74
  +++ tcp_input.c	1998/05/04 17:59:52	1.75
  @@ -680,7 +680,9 @@
   		 * - otherwise do a normal 3-way handshake.
   		if ((to.to_flag & TOF_CC) != 0) {
  -		    if (taop->tao_cc != 0 && CC_GT(to.to_cc, taop->tao_cc)) {
  +		    if (tp->t_state & TF_NOPUSH &&
  +			taop->tao_cc != 0 && CC_GT(to.to_cc, taop->tao_cc)) {
   			taop->tao_cc = to.to_cc;
   			tp->t_state = TCPS_ESTABLISHED;
FreeBSD, Inc.

Web Site:             
Confidential contacts:          security-officer at
Security notifications:         security-notifications at
Security public discussion:     freebsd-security at
PGP Key:      

Notice: Any patches in this document may not apply cleanly due to
        modifications caused by digital signature or mailer software.
        Please reference the URL listed at the top of this document
        for original copies of all patches if necessary.

Version: 2.6.2


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