MCI Telecommunications internetMCI Security Group Report Title: iMCI MIIGS Security Alert Report Name: Vulnerability in Unix "at" Report Number: iMCISE:IMCICIAC:061597:01:P1R1 Report Date: 06/14/97 Report Format: Formal Report Classification: MCI Informational Report Reference: http://www.security.mci.net Report Distribution: iMCI Security, MCI Internal Internet Gateway Security (MIIGS), MCI Emergency Alert LiSt (MEALS) (names on file) -------------------------------------------------------------------------- -----BEGIN PGP SIGNED MESSAGE----- *******************************FOR PUBLIC RELEASE **************************** __________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Vulnerability in the at(1) program June 13, 1997 19:00 GMT Number H-71 ______________________________________________________________________________ PROBLEM: A buffer overflow condition exists in some implementations of the at(1) program. PLATFORM: See "Appendix A - Vendor Information" below for platforms affected. DAMAGE: Local users may gain root privileges. SOLUTION: If your system is vulnerable, install vendor patches or apply the workaround described in Section III.B. ______________________________________________________________________________ VULNERABILITY The vulnerability exists on multiple platforms. ASSESSMENT: ______________________________________________________________________________ [****** Start CERT Advisory ******] ============================================================================= CERT* Advisory CA-97.18 Original issue date: June 12, 1997 Last revised: June 12, 1997 Section IIIA and Appendix A - Added vendor information for Digital Equipment Corporation. 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. 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. 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. [****** End CERT Advisory ******] ____________________________________________________________________________ ___ CIAC wishes to acknowledge the contributions of Dan Farmer, Wolfgang Ley of DFN-CERT, and the CERT Coordination Center 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. 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World Wide Web: http://ciac.llnl.gov/ Anonymous FTP: ciac.llnl.gov (198.128.39.53) Modem access: +1 (510) 423-4753 (28.8K baud) +1 (510) 423-3331 (28.8K baud) CIAC has several self-subscribing mailing lists for electronic publications: 1. CIAC-BULLETIN for Advisories, highest priority - time critical information and Bulletins, important computer security information; 2. CIAC-NOTES for Notes, a collection of computer security articles; 3. SPI-ANNOUNCE for official news about Security Profile Inspector (SPI) software updates, new features, distribution and availability; 4. SPI-NOTES, for discussion of problems and solutions regarding the use of SPI products. Our mailing lists are managed by a public domain software package called Majordomo, which ignores E-mail header subject lines. 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If you are not part of these communities, please contact your agency's response team to report incidents. 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. 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