============================================================================= CA-93:17 CERT Advisory November 11, 1993 xterm Logging Vulnerability ----------------------------------------------------------------------------- The CERT Coordination Center is working on eliminating a vulnerability in xterm. This vulnerability potentially affects all systems running xterm with the setuid or setgid bit set. This vulnerability has been found in X Version 11, Release 5 (X11R5) and earlier versions of X11. CERT is working with the vendor community to address this vulnerability. ----------------------------------------------------------------------------- I. Description A vulnerability in the logging function of xterm exists in many versions of xterm that operate as a setuid or setgid process. The vulnerability allows local users to create files or modify any existing files. If the setuid or setgid privilege bit is not set on the xterm program, the vulnerability cannot be exploited. It is possible that the xterm on your system does not allow logging. In this case, the vulnerability cannot be exploited. To determine if logging is enabled, run xterm with the "-l" option. If an "XtermLog.axxxx" file is created in the current directory, xterm supports logging. You can also check the output of "xterm -help" to see whether the "-l" option is described as "not supported". Another way to determine if logging is available is to look for the "Log to File" item in the Main Options menu (press Control mouse button 1). If the X Consortium's public patch has been installed as distributed, the option "Log to File" should not appear in the menu. II. Impact This vulnerability allows anyone with access to a user account to gain root access. III. Solutions All of the following solutions require that a new version of xterm be installed. When installing the new xterm, it is important either to remove the old version of xterm or to clear the setuid and setgid bits from the old xterm. CERT suggests one of the following solutions. A. Install vendor supplied patch if available. CERT is hopeful that patches will be forthcoming. We will be maintaining a status file, xterm-patch-status, and we will add patch availability information to this file as it becomes known. The file is available via anonymous FTP from info.cert.org. The name of the file is pub/cert_advisories/xterm-patch-status. A current version of this file is appended to this Advisory. For more up-to-date information, contact the vendor. B. If your site is using the X Consortium's X11R5, install the public patch #26. This patch is available via anonymous FTP from ftp.x.org as the file /pub/R5/fixes/fix-26. Install all patch files up to and including fix-26. By default, the patch disables logging. If you choose to enable logging, a variation of the vulnerability still exists. Checksum information: BSD Unix Sum: 19609 47 System V Sum: 51212 94 MD5 Checksum: e270560b6e497a0a71881d4ff4db8c05 C. If your site is using an earlier version of the X Consortium's X11, upgrade to X11R5. Install all patches up to and including fix-26. D. If you are unable to upgrade to the X Consortium's X11R5, modify the xterm source code to remove the logging feature. Familiarity with X11 and its installation and configuration is recommended before implementing these modifications. --------------------------------------------------------------------------- The CERT Coordination Center wishes to thank Stephen Gildea of the X Consortium for his assistance in responding to this problem. --------------------------------------------------------------------------- If you believe that your system has been compromised, contact the CERT Coordination Center or your representative in Forum of Incident Response and Security Teams (FIRST). Internet E-mail: cert@cert.org Telephone: 412-268-7090 (24-hour hotline) CERT personnel answer 8:30 a.m.-5:00 p.m. EST(GMT-5)/EDT(GMT-4), and are on call for emergencies during other hours. CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh, PA 15213-3890 Past advisories, information about FIRST representatives, and other information related to computer security are available for anonymous FTP from info.cert.org.  --------------------------------------------------------------------------- CERT Coordination Center xterm Vendor Status November 11, 1993 This file is a supplement to the CERT Advisory CA-93:17 of November 11, 1993, and will be updated as additional information becomes available. The following is vendor-supplied information. The CERT Coordination Center will not formally review, evaluate, or endorse this information. For more up-to-date information, contact your vendor. It is important to note that the vendor of your xterm may not be the same as the vendor of your platform. You should take care to correctly identify the vendor whose xterm you are using, so you can take the appropriate action. Convex Fixed in CXwindows V3.1. Fixed in CXwindows V3.0 with TAC patch V3.0.131 applied. The Convex Technical Assistance Center is available for additional information at 800-952-0379. Cray Fixed. Contact Cray for version/patch numbers. DEC/OSF Attached is the information on the remedial images to address the xterm issue for ULTRIX V4.3 (VAX & RISC) and OSF/1 V1.2. The solutions have been included in ULTRIX V4.4 (VAX & RISC) and OSF/1 V1.3. Customers may call their normal Digital Multivendor Customer Services Support Channel to obtain this kit. ---------------------------------------------------------- *ULTRIX,OSF/1] CSCPAT_4034 xterm Security Fix ECO Summary COPYRIGHT (c) 1988, 1993 by Digital Equipment Corporation. ALL RIGHTS RESERVED. COMPONENT: xterm OP/SYS: ULTRIX VAX and RISC, OSF/1 SOURCE: Digital Customer Support Center ECO INFORMATION: CSCPAT Kit: CSCPAT_4034 V1.1 CSCPAT Kit Size: 2152 blocks Engineering Cross Reference: SSRT93-E-0230, SSRT93-E-0231, SSRT93-E-232 Kit Applies To: ULTRIX V4.3, OSF/1 V1.2 System Reboot Required: NO ---------------------------------------------------------- SCO The current releases listed below are not vulnerable to this problem. No xterm logging or scoterm logging is provided: SCO Open Desktop Lite, Release 3.0 SCO Open Desktop, Release 3.0 SCO Open Server Network System, Release 3.0 SCO Open Server Enterprise System, Release 3.0 Contact SCO for any further information. Sequent Fixed. Contact Sequent for version/patch numbers. Sun Sun's version of xterm has not been setuid root since at least as far back as SunOS 4.1.1, and probably further. An xterm that does not run setuid or setgid is not vulnerable to the xterm logging problem. CAUTION: A Sun patch was issued on December 6, 1992 to give system administrators the option of running xterm setuid root. Installing this patch will introduce the xterm logging vulnerability. So check your xterm. If either the setuid or setgid privilege bit is set on the xterm program, the vulnerability can be exploited. Contact Sun for further information. X.org (Publicly distributed version of X.) You can patch X11R5 by applying all patches up to and including fix-26. See the associated CERT Advisory (CA-93:17) for further information.