************************************************************************** Security Bulletin 9546 DISA Defense Communications System December 1, 1995 Published by: DISN Security Coordination Center (SCC@NIC.DDN.MIL) 1-(800) 365-3642 DEFENSE INFORMATION SYSTEM NETWORK SECURITY BULLETIN The DISN SECURITY BULLETIN is distributed by the DISN SCC (Security Coordination Center) under DISA contract as a means of communicating information on network and host security exposures, fixes, and concerns to security and management personnel at DISN facilities. Back issues may be obtained via FTP (or Kermit) from NIC.DDN.MIL [192.112.36.5] using login="anonymous" and password="guest". The bulletin pathname is scc/sec-yynn (where "yy" is the year the bulletin is issued and "nn" is a bulletin number, e.g. scc/sec-9544.txt). These are also available at our WWW site, http://nic.ddn.mil. ************************************************************************** + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + ! ! ! The following important advisory was issued by the Automated ! ! Systems Security Incident Support Team (ASSIST) and is being ! ! relayed unedited via the Defense Information Systems Agency's ! ! Security Coordination Center distribution system as a means ! ! of providing DISN subscribers with useful security information. ! ! ! + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + -----BEGIN PGP SIGNED MESSAGE----- <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Automated Systems Security Incident Support Team _____ ___ ___ _____ ___ _____ | / /\ / \ / \ | / \ | | / Integritas / \ \___ \___ | \___ | | < et /____\ \ \ | \ | | \ Celeritas / \ \___/ \___/ __|__ \___/ | |_____\ <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Bulletin 95-43 Release date: 30 November, 1995, 1:00 PM EDT (GMT -4) SUBJECT: X Authentication Vulnerability. SUMMARY: Two widely used X Window System authorization schemes have weaknesses in the sample implementation. These weaknesses are present in X11 Release 6 and earlier releases of the X11 sample implementation and could allow unauthorized remote users to connect to X displays. There are reports that Internet systems have been broken into using at least one of these weaknesses and that there are exploit programs are available. BACKGROUND: On systems on which xdm is built without the HasXdmAuth config option, the MIT-MAGIC-COOKIE-1 key generated by xdm may be guessable. If you use MIT-MAGIC-COOKIE-1 to authenticate X connections, and your keys are generated by xdm, and xdm does not also support XDM-AUTHORIZATION-1 authentication (that is, your X tree was not built with the HasXdmAuth config option), you may be at risk. On systems with poor pseudo-random number generators, the key may be guessable by remote users. On other systems, users with access to the file system where xdm stores its keys for use by local servers may be able to use information in the file system to guess the key. If your xdm program was built with HasXdmAuth set to YES (the compiler command line includes the -DHASXDMAUTH flag), MIT-MAGIC-COOKIE-1 keys generated by xdm are not vulnerable; the DES code is used to generate cryptographically secure keys. IMPACT: Remote users may be able to connect to your X display server. RECOMMENDED SOLUTIONS: Patches - ------- Install a vendor supplied patch if available. If your site is using X11 built from X Consortium X11R6 sources, install public patch #13. This patch is available via anonymous FTP from ftp.x.org as the file /pub/R6/fixes/fix-13. It is also available from the many sites that mirror ftp.x.org. Apply all patches not already applied, up to and including fix-13. The file xc/bug-report shows what public patches have been already applied to your source tree. The MD5 checksum of fix-13 is as follows: MD5 (fix-13) = 0d81d843acf803a8bedf90d3a18b9ed6 If your site is using an earlier version of the X Consortium's X11, upgrade to X11R6. Install all patches up to and including fix-13. Workarounds - ----------- (1) Building with HasXdmAuth will eliminate the first vulnerability. (2) If you cannot use DES, you can determine your exposure to remote attackers by testing the strength of your rand() function using the program rand-test; the source is available as . (3) Limiting use of X connections using XDM-AUTHORIZATION-1 to trusted networks will prevent unauthorized parties from snooping X protocol traffic, thus preventing exploitation of the second vulnerability. Vendor Vulnerability Status Information - --------------------------------------- The following information was supplied by vendors and has not been verified. Cray Research. UNICOS 8.0 and 9.0 are not vulnerable. These systems have robust pseudo-random number generators, making them not vulnerable to the first problem, and do not support an X server, making them not vulnerable to the second problem. GSSC (formerly Solbourne). Has concluded they are not vulnerable. Hewlett-Packard. All versions of X on HP-UX 9.x and 10.x (based on X11R5) do not have the first vulnerability. X Consortium. (Sample implementation of X.) You can patch X11R6 by applying all public patches up to and including fix-13. Patches are available via FTP from ftp.x.org in /pub/R6/fixes/ and from mirroring sites. You can check that the X server has fix-13 installed by verifying that the server has a vendor release number of 6001 or higher. General questions about the X Window System can be asked on the xpert mailing list hosted at x.org. Send a "subscribe" message to xpert-request@x.org to subscribe. This list is gatewayed with the comp.windows.x newsgroup. The FAQ for this newsgroup is available from and other locations. describes other newsgroups and mailing lists for the discussion of issues related to the X Window System. Bugs encounted in X Consortium code can be reported to xbugs@x.org using the format in xc/bug-report. Please see the X11R6 Release Notes for additional details. XFree86 Project The XFree86 Project, Inc has patched binaries for XFree86 version 3.1.2 running on FreeBSD 1.1.5, FreeBSD 2.0.5, ISC, NetBSD and SVR4. They are available from ftp://ftp.xfree86.org/pub/XFree86/3.1.2/binaries/ The files are: FreeBSD-1.1.5/X312Sxdm.tgz FreeBSD-2.0.5/X312Sxdm.tgz ISC/X312Sxdm.tgz NetBSD/X312Sxdm.tgz SVR4/X312Sxdm.tgz The MD5 checksums are: MD5 (FreeBSD-1.1.5/X312Sxdm.tgz) = 43166109c88fcd623d27de1fa90e8f5b MD5 (FreeBSD-2.0.5/X312Sxdm.tgz) = 3314a623b2c31a9130445e9237ff65f9 MD5 (ISC/X312Sxdm.tgz) = e4e16fc5f4d06ad455e572a2e1eb0eb5 MD5 (NetBSD/X312Sxdm.tgz) = 0bc74cbee0214366ac15658bf5436853 MD5 (SVR4/X312Sxdm.tgz) = bf5dfea2a86cdf92621421e3f68af203 Installation instructions (assuming X312xdm.tgz is in /tmp): Kill any xdm processes that are running, then: For FreeBSD 1.1.5 and FreeBSD 2.0.5: cd /usr mv X11R6/bin/xdm X11R6/bin/xdm-3.1.2 chmod 0500 X11R6/bin/xdm-3.1.2 gzip -d < /tmp/X312xdm.tgz | tar vxf - For NetBSD: mv /usr/X11R6/bin/xdm /usr/X11R6/bin/xdm-3.1.2 chmod 0500 /usr/X11R6/bin/xdm-3.1.2 pkg_add /tmp/X312Sxdm.tgz For ISC and SVR4: cd /usr/X11R6 mv bin/xdm bin/xdm-3.1.2 chmod 0500 bin/xdm-3.1.2 gzip -d < /tmp/X312xdm.tgz | tar vxf - <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> ASSIST would like to thank the CERT Coordination Center and the X Consortium for information contained in this bulletin. <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> ASSIST is an element of the Defense Information Systems Agency (DISA), Center for Information Systems Security (CISS), that provides service to the entire DoD community. Constituents of the DoD with questions about ASSIST or computer security issues, can contact ASSIST using one of the methods listed below. Non-DoD organizations/ institutions, contact the Forum of Incident Response and Security Teams (FIRST) representative. To obtain a list of FIRST member organizations and their constituencies send an email to docserver@first.org with an empty "subject" line and a message body containing the line "send first-contacts". ASSIST Information Resources: To be included in the distribution list for the ASSIST bulletins, send your Milnet (Internet) e-mail address to assist-request@assist.mil. Back issues of ASSIST bulletins, and other security related information, are available from the ASSIST BBS at 703-607-4710, 327-4710, and through anonymous FTP from assist.mil (IP address 199.211.123.11). Note: assist.mil will only accept anonymous FTP connections from Milnet addresses that are registered with the NIC or DNS. If your system is not registered, you must provide your MILNET IP address to ASSIST before access can be provided. ASSIST Contact Information: PHONE: 800-357-4231, COMM 703-607-4700, DSN 327-4700. ELECTRONIC MAIL: assist@assist.mil. ASSIST BBS: COMM 703-607-4710, DSN 327-4710, leave a message for the "sysop". FAX: COMM 703-607-4735, DSN 607-4735 ASSIST uses Pretty Good Privacy (PGP) 2.6.2 as the digital signature mechanism for bulletins. PGP 2.6.2 incorporates the RSAREF(tm) Cryptographic Toolkit under license from RSA Data Security, Inc. A copy of that license is available via anonymous FTP from net-dist.mit.edu (IP 18.72.0.3) in the file /pub/PGP/rsalicen.txt, and through the world wide web from http://net-dist.mit.edu/pgp.html. In accordance with the terms of that license, PGP 2.6.2 may be used for non-commercial purposes only. Instructions for downloading the PGP 2.6.2 software can also be obtained from net-dist.mit.edu in the pub/PGP/README file. PGP 2.6.2 and RSAREF may be subject to the export control laws of the United States of America as implemented by the United States Department of State Office of Defense Trade Controls. The PGP signature information will be attached to the end of ASSIST bulletins. Reference herein to any specific commercial product, process, or service by trade name, trademark manufacturer, or otherwise, does not constitute or imply its endorsement, recommendation, or favoring by ASSIST. 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If you are not part of the DOD community, please contact your agency's incident response team to report incidents. Your agency's team will coordinate with DOD. 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 by sending email to docserver@first.org with an empty subject line and a message body containing the line: send first-contacts. This document was prepared as an service to the DOD community. Neither the United States Government nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, 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. The opinions of the authors expressed herein do not necessarily state or reflect those of the United States Government, and shall not be used for advertising or product endorsement purposes.