-----BEGIN PGP SIGNED MESSAGE----- ============================================================================= CERT* Advisory CA-97.18 Original issue date: June 12, 1997 Last revised: June 25, 1997 Section IIIA and Appendix A - Added vendor information for Berkeley Software Design, Inc. (BSDI). A complete revision history is at the end of this file. Topic: Vulnerability in the at(1) program - ----------------------------------------------------------------------------- The CERT Coordination Center has received reports of a buffer overflow condition in some versions of the at(1) program. By carefully specifying the data that overflows this buffer, any user can execute arbitrary commands as root. The CERT/CC team recommends installing a vendor patch if one is available (see Section III.A). Until you can do so, we recommend disabling at(1) (see Section III.B). We will update this advisory as we receive additional information. Please check advisory files regularly for updates that relate to your site. - ----------------------------------------------------------------------------- I. Description The at(1) program can be used by local users to schedule commands to be executed at a later time. When those commands are run, they are run as the user who originally ran at(1). That user will be referred to as the scheduling user. As a precaution, the scheduling user's list of commands is stored in a file in a directory that is not writable by other users. The file's ownership is changed to that of the scheduling user, and that information is used to define the identity of the process that runs the commands when the appointed time arrives. These measures are intended to prevent other users from changing the scheduling user's list of commands or creating new lists to be executed as another user. To achieve this additional level of security, the at(1) program runs as set-user-id root. Some versions of at(1) contain a programming defect that can result in a buffer local to at(1) being overflowed. Through the careful specification of the data that overflows this buffer, arbitrary commands can be executed with the identity of at(1) process, root in this case. II. Impact Any user with an account on a system that contains a defective version of at(1) can execute programs as root. III. Solution A. Install a patch from your vendor Below is a list of vendors who have provided information about at. Details are in Appendix A of this advisory; we will update the appendix as we receive more information. If your vendor's name is not on this list, the CERT/CC did not hear from that vendor. Please contact your vendor directly. Berkeley Software Design, Inc. (BSDI) Cray Research - A Silicon Graphics Company Digital Equipment Corporation Hewlett-Packard Company IBM Corporation Santa Cruz Operation, Inc. (SCO) Silicon Graphics, Inc. Sun Microsystems, Inc. B. Until you are able to install the appropriate patch, we recommend the following workaround: Turn off at(1) by setting its mode to 0. Do the following as root: # chmod 0 /usr/bin/at Note that the location of at(1) varies from system to system. Consult your system's documentation for the correct location. After you turn off the at(1) command, users will not be able to use it. As an alternative to at(1), consider using the crontab(1) command if your system provides it. ........................................................................... Appendix A - Vendor Information Below is a list of the vendors who have provided information for this advisory. We will update this appendix as we receive additional information. If you do not see your vendor's name, the CERT/CC did not hear from that vendor. Please contact the vendor directly. Berkeley Software Design, Inc. (BSDI) ===================================== No versions of BSD/OS are succeptible to this problem. Cray Research - A Silicon Graphics Company ========================================== Neither Unicos nor Unicos/mk is believed to be vulnerable. Digital Equipment Corporation ============================= Copyright (c) Digital Equipment Corporation 1997. All rights reserved. Information about this reported problem, and subsequent attempts to reproduce the problem have been unsuccessful for Digital's ULTRIX or Digital UNIX Operating Systems Software. Should further information or testing indicate this problem can be reproduced on Digital's products, a solution will be provided accordingly. At that time Digital will provide notice of the completion/availability of the patches through AES services (DIA, DSNlink FLASH) and be available from your normal Digital Support channel. DIGITAL EQUIPMENT CORPORATION 6/09/97 ----------------------------- ---------- Hewlett-Packard Company ======================= Hewlett Packard is currently investigating the problem. We will update this advisory through the CERT/CC when the investigation is complete. IBM Corporation =============== See the appropriate release below to determine your action. AIX 3.2 ------- Apply the following fixes to your system: PTF - U443452 U443486 U444191 U444206 U444213 U444243 APAR - IX60796 To determine if you have these PTFs on your system, run the following commands: lslpp -lB U443452 U443486 U444191 U444206 U444213 U444243 AIX 4.1 ------- Apply the following fixes to your system: APAR - IX60894 APAR - IX60890 To determine if you have this APAR on your system, run the following commands: instfix -ik IX60894 instfix -ik IX60890 Or run the following commands: lslpp -h bos.rte.cron lslpp -h bos.rte.libc Your version of bos.rte.cron should be 4.1.4.8 or later. Your version of bos.rte.libc should be 4.1.4.18 or later. AIX 4.2 ------- Apply the following fixes to your system: APAR - IX60892 APAR - IX61125 To determine if you have this APAR on your system, run the following commands: instfix -ik IX60892 instfix -ik IX61125 Or run the following commands: lslpp -h bos.rte.cron lslpp -h bos.rte.libc Your version of bos.rte.cron should be 4.2.0.1 or later. Your version of bos.rte.libc should be 4.2.0.5 or later. To Order -------- APARs may be ordered using Electronic Fix Distribution (via FixDist) or from the IBM Support Center. For more information on FixDist, reference URL: http://service.software.ibm.com/aixsupport/ or send e-mail to aixserv@austin.ibm.com with a subject of "FixDist". IBM and AIX are registered trademarks of International Business Machines Corporation. Santa Cruz Operation, Inc. (SCO) ================================ All SCO operating systems are vulnerable. SCO has made an interim fix available for anonymous ftp: ftp://ftp.sco.com/SSE/sse007.ltr.Z - cover letter ftp://ftp.sco.com/SSE/sse007.tar.Z - replacement binaries The fix includes binaries for the following SCO operating systems: - SCO CMW+ 3.0 - SCO Open Desktop/Open Server 3.0, SCO UNIX 3.2v4 - SCO OpenServer 5.0 - SCO UnixWare 2.1 Silicon Graphics, Inc. ====================== At this time, Silicon Graphics does not have any public information for the at(1) issue. Silicon Graphics has communicated with CERT and other external security parties and is actively investigating this issue. When more Silicon Graphics information (including any possible patches) is available for release, that information will be released via the SGI security mailing list, wiretap. For subscribing to the wiretap mailing list and other SGI security related information, please refer to the Silicon Graphics Security Headquarters website located at: http://www.sgi.com/Support/Secur/security.html Sun Microsystems, Inc. ====================== Sun will be producing patches. - ----------------------------------------------------------------------------- Technical information for this advisory was drawn in part from a posting by Don Farmer to the bugtraq mailing list. Thanks to Wolfgang Ley of DFN-CERT for his help in developing this advisory. - ----------------------------------------------------------------------------- If you believe that your system has been compromised, contact the CERT Coordination Center or your representative in the Forum of Incident Response and Security Teams (see http://www.first.org/team-info). CERT/CC Contact Information - ---------------------------- Email cert@cert.org Phone +1 412-268-7090 (24-hour hotline) CERT personnel answer 8:30-5:00 p.m. EST(GMT-5) / EDT(GMT-4) and are on call for emergencies during other hours. Fax +1 412-268-6989 Postal address CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh PA 15213-3890 USA Using encryption We strongly urge you to encrypt sensitive information sent by email. We can support a shared DES key or PGP. Contact the CERT/CC for more information. Location of CERT PGP key ftp://info.cert.org/pub/CERT_PGP.key Getting security information CERT publications and other security information are available from http://www.cert.org/ ftp://info.cert.org/pub/ CERT advisories and bulletins are also posted on the USENET newsgroup comp.security.announce To be added to our mailing list for advisories and bulletins, send email to cert-advisory-request@cert.org In the subject line, type SUBSCRIBE your-email-address - --------------------------------------------------------------------------- Copyright 1997 Carnegie Mellon University This material may be reproduced and distributed without permission provided it is used for non-commercial purposes and the copyright statement is included. * Registered U.S. Patent and Trademark Office. - --------------------------------------------------------------------------- This file: ftp://info.cert.org/pub/cert_advisories/CA-97.18.at http://www.cert.org click on "CERT Advisories" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Revision history June 25, 1997 Section IIIA and Appendix A - Added vendor information for Berkeley Software Design, Inc. (BSDI). June 12, 1997 Section IIIA and Appendix A - Added vendor information for Digital Equipment Corporation. -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBM7EyDHVP+x0t4w7BAQEJ6QQAy9j1UGEMFM1017+atqbXNzZ5Y8Buskx5 WvNBH0DeakCgnf8qgnXX/IqcJLyMeVAD/C0A200cPJBG2ANgg8T9StFYODIm5Nds VqN9+iRdf1LkxvsQPUajgAM1L4C9T/ELy4R9D1IT8FM2IXEKspUmwSlbXbYtlLQV T7wz63+LIiE= =V2Sl -----END PGP SIGNATURE-----