-----BEGIN PGP SIGNED MESSAGE----- __________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN FreeBSD T/TCP Vulnerability May 19, 1998 21:00 GMT Number I-051 ______________________________________________________________________________ PROBLEM: FreeBSD had identified a vulnerability in the T/TCP, extension for transactions to TCP PLATFORM: FreeBSD 2.1.* FreeBSD 2.2.*, FreeBSD-2.2-stable before 1998/05/14 and FreeBSD-3.0-current before 1998/05/05.Any other system incorporating TTCP extentions may be affected. DAMAGE: If exploited, the hole may be used to obtain unauthorized access to the system by spoofing connections to the r*-services. SOLUTION: Apply patch or workaround ______________________________________________________________________________ VULNERABILITY CIAC recommends that action to correct this problem be takes as ASSESSMENT: soon as possible if your systems is vulnerable. ______________________________________________________________________________ [ Start FreeBSD Advisory ] 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 ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-98:03/ttcp.orig 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 affected. 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 transactions. 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 connections. 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 ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-98:03/ 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. ========================================================================= [ End FreeBSD Advisory ] ______________________________________________________________________________ CIAC wishes to acknowledge the contributions of FreeBSD, Inc. for the information contained in this bulletin. ______________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. 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Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. 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