AUSCERT External Security Bulletin Redistribution
   ESB-98.075 -- REVISED FreeBSD Security Advisory - FreeBSD-SA-98:03.ttcp
                            Vulnerability in ttcp
                                19th May 1998


The FreeBSD Security Team has released the following advisory concerning a 
vulnerability in an extension to TCP called "TCP Extensions for Transactions".  

The following security bulletin is provided as a service to AusCERT's
members.  As AusCERT did not write this document, AusCERT has had no
control over its content.  As such, the decision to use any or all of this
information is the responsibility of each user or organisation, and should
be done so in accordance with site policies and procedures.

NOTE: This is only the original release of the security bulletin.  It will
not be updated when the original bulletin is.  If downloading at a later
date, it is recommended that the bulletin is retrieved from the original
authors to ensure that the information is still current.

Contact information for FreeBSD is included in the Security Bulletin below.  
If you have any questions or need further information, please contact them 

Previous advisories and external security bulletins can be retrieved from:


If you believe that your system has been compromised, contact AusCERT or
your representative in FIRST (Forum of Incident Response and Security

Internet Email: auscert@auscert.org.au
Facsimile:	(07) 3365 7031
Telephone:	(07) 3365 4417 (International: +61 7 3365 4417)
		AusCERT personnel answer during Queensland business hours
		which are GMT+10:00 (AEST).
		On call after hours for emergencies.

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WARNING: The patch given in the original advisory had an error. You should
apply the patch in this advisory. In order to do so, you should have the
original file. If you do no longer have the original, look at
It contains the original patch. You should then apply it first using patch
with the -R option.
We're sorry for any inconvenience this may cause.

This advisory also contains a valid patch for FreeBSD 2.1.* versions.

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

Topic:          Problems with TTCP

Category:       core
Module:         kernel
Announced:      1998-05-14, revised at 1998-05-18
Affects:        FreeBSD 2.1.*
		FreeBSD 2.2.*,
		FreeBSD-2.2-stable before 1998/05/14 and
		FreeBSD-3.0-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-2.1-stable as of 1998/05/18
FreeBSD only:   No. Any other system incorporating TTCP extentions may be

Patches:        ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-98:03/

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 2.1.* systems,
     for 2.1-stable, for 2.2.* systems, for 2.2-stable and for 3.0-current.

     The patch below can be found on

  Index: tcp_input.c
  RCS file: /home/ncvs/src/sys/netinet/tcp_input.c,v
  retrieving revision 1.74
  retrieving revision 1.77
  diff -u -r1.74 -r1.77
  --- tcp_input.c	1998/04/24 10:08:57	1.74
  +++ tcp_input.c	1998/05/18 17:11:24	1.77
  @@ -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_flags & TF_NOPUSH) != 0) &&
  +			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:                       http://www.freebsd.org/
Confidential contacts:          security-officer@freebsd.org
Security notifications:         security-notifications@freebsd.org
Security public discussion:     freebsd-security@freebsd.org
PGP Key:                ftp://ftp.freebsd.org/pub/FreeBSD/CERT/public_key.asc

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: 2.6.3ia
Charset: noconv


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Version: 2.6.3i
Charset: noconv
Comment: ftp://ftp.auscert.org.au/pub/auscert/AUSCERT_PGP.key