-----BEGIN PGP SIGNED MESSAGE----- =============================================================================== Security Advisory CERT-NL =============================================================================== Author/Source : Egon Verharen/Nico de Koo Index : S-98-28 Distribution : World Page : 1 Classification: External Version: 2 Subject : TTCP vulnerability Date : 22-May-98 =============================================================================== By courtesy of FreeBSD, Inc. we received information on a vulnerability in TCP Extensions for Transactions, or shortly T/TCP, where under certain circumstances, complete connections can be spoofed. CERT-NL recommends to follow the FreeBSD recommendation, which is to disable all r-* services, or for FreeBSD 2.2.* and 3.0 systems install the appropriate patches. ============================================================================== FreeBSD-SA-98:03 Security Advisory FreeBSD, Inc. 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. ============================================================================== CERT-NL is the Computer Emergency Response Team for SURFnet customers. SURFnet is the Dutch network for educational, research and related institutes. CERT-NL is a member of the Forum of Incident Response and Security Teams (FIRST). All CERT-NL material is available under: http://www.surfnet.nl/surfnet/security/cert-nl.html ftp://ftp.surfnet.nl/surfnet/net-security In case of computer or network security problems please contact your local CERT/security-team or CERT-NL (if your institute is NOT a SURFnet customer please address the appropriate (local) CERT/security-team). CERT-NL is one/two hour(s) ahead of UTC (GMT) in winter/summer, i.e. UTC+0100 in winter and UTC+0200 in summer (DST). Email: cert-nl@surfnet.nl ATTENDED REGULARLY ALL DAYS Phone: +31 302 305 305 BUSINESS HOURS ONLY Fax: +31 302 305 329 BUSINESS HOURS ONLY Snailmail: SURFnet bv Attn. CERT-NL P.O. Box 19035 NL - 3501 DA UTRECHT The Netherlands NOODGEVALLEN: 06 52 87 92 82 ALTIJD BEREIKBAAR EMERGENCIES : +31 6 52 87 92 82 ATTENDED AT ALL TIMES CERT-NL'S EMERGENCY PHONENUMBER IS ONLY TO BE USED IN CASE OF EMERGENCIES: THE SURFNET HELPDESK OPERATING THE EMERGENCY NUMBER HAS A *FIXED* PROCEDURE FOR DEALING WITH YOUR ALERT AND WILL IN REGULAR CASES RELAY IT TO CERT-NL IN AN APPROPRIATE MANNER. CERT-NL WILL THEN CONTACT YOU. ============================================================================== -----BEGIN PGP SIGNATURE----- Version: 2.6.3i Charset: cp850 iQCVAwUBNWU2m1pSTqmIRWKVAQGhvAQAsf0E4x8UINS1SOHgfcS7pLY+3AWjvdNa 1BCAfBmzYhNrwVTfCdPoawNX5dMz1GQi/75Mmshu0VCObLr83qDX3T1E3qtgnTSh u8+Q1BbHNCt4JxyD9rDCwsgA/+oJL0Is670VowbwFuZ8rYorNLu4u5ZQ4xVpo0Z5 TQrsmBDy3iQ= =KDxz -----END PGP SIGNATURE-----