__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN FreeBSD sort Uses Insecure Temporary Files February 1, 2001 17:00 GMT Number L-039 ______________________________________________________________________________ PROBLEM: During internal auditing, sort(1) was found to use easily predictable temporary file names. It does create these temporary files correctly such that they cannot be "subverted" by a symlink attack, but the program will abort if the temporary filename chosen is already in use. PLATFORM: FreeBSD 3.x (all releases), FreeBSD 4.x (all releases prior to 4.2), FreeBSD 3.5-STABLE prior to the correction date. DAMAGE: Attackers can cause the operation of sort(1) to fail, possibly disrupting aspects of system operation. SOLUTION: Upgrade the vulnerable FreeBSD system to FreeBSD 3.5-STABLE, 4.2-RELEASE, or 4.2-STABLE after the correction date or patch your present system. Refer to section V. of this bulletin for additional information. ______________________________________________________________________________ VULNERABILITY The risk is MEDIUM. An attacker could cause the sort(1) command ASSESSMENT: to abort resulting in management scripts that rely on sort to miss malicious system activity. ______________________________________________________________________________ [****** Start FreeBSD Advisory ******] ============================================================================= FreeBSD-SA-01:13 Security Advisory FreeBSD, Inc. Topic: sort uses insecure temporary files Category: core Module: sort Announced: 2001-01-29 Credits: Discovered during internal auditing Affects: FreeBSD 3.x (all releases), FreeBSD 4.x (all releases prior to 4.2), FreeBSD 3.5-STABLE prior to the correction date. Corrected: 2000-11-11 (FreeBSD 4.1.1-STABLE) 2001-01-01 (FreeBSD 3.5-STABLE) FreeBSD only: NO I. Background sort(1) is a program to sort lines of text. It is externally maintained, contributed software which is included in FreeBSD by default. II. Problem Description During internal auditing, sort(1) was found to use easily predictable temporary file names. It does create these temporary files correctly such that they cannot be "subverted" by a symlink attack, but the program will abort if the temporary filename chosen is already in use. This allows an attacker to cause the sort(1) command to abort, which may have a cascade effect on other scripts which make use of it (such as system management and reporting scripts). For example, it may be possible to use this failure mode to hide the reporting of malicious system activity which would otherwise be detected by a management script. All released versions of FreeBSD prior to the correction date including FreeBSD 3.5.1 and FreeBSD 4.1.1 are vulnerable. The problem was corrected prior to the release of FreeBSD 4.2. III. Impact Attackers can cause the operation of sort(1) to fail, possibly disrupting aspects of system operation. IV. Workaround None appropriate. V. Solution One of the following: Upgrade the vulnerable FreeBSD system to FreeBSD 3.5-STABLE, 4.2-RELEASE, or 4.2-STABLE after the correction date. To patch your present system: download the relevant patch from the below location, and execute the following commands as root: [FreeBSD 4.1.1 base system] # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-01:13/sort- 4.1.1.patch # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-01:13/sort- 4.1.1.patch.asc Verify the detached PGP signature using your PGP utility. # cd /usr/src/gnu/usr.bin/sort # patch -p < /path/to/patch # make depend && make all install [FreeBSD 3.5.1 base system] # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-01:13/sort- 3.5.1.patch # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-01:13/sort- 3.5.1.patch.asc Verify the detached PGP signature using your PGP utility. # cd /usr/src/gnu/usr.bin/sort # patch -p < /path/to/patch # make depend && make all install [****** End FreeBSD Advisory ******] ______________________________________________________________________________ CIAC wishes to acknowledge the contributions of FreeBSD 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. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be contacted at: Voice: +1 925-422-8193 (7x24) FAX: +1 925-423-8002 STU-III: +1 925-423-2604 E-mail: ciac@llnl.gov Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. World Wide Web: http://www.ciac.org/ (or http://ciac.llnl.gov -- they're the same machine) Anonymous FTP: ftp.ciac.org (or ciac.llnl.gov -- they're the same machine) PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing communities receive CIAC bulletins. 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. 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 or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC) L-029: FreeBSD "ipfw/ip6fw" Vulnerability L-030: Four Vulnerabilities in ISC Bind L-031: Sun AnswerBook2 Vulnerability L-032: Class Loading Vulnerability in Sun Java (TM) Runtime Environment L-033: Sun Java Web Server Vulnerability L-034: HP Security Vulnerability in man(1) Command L-035: HP-UX Support Tools Manager Vulnerability L-036: FreeBSD procfs Vulnerabilities L-037: FreeBSD periodic Uses Insecure Temporary Files L-038: FreeBSD inetd ident Server Vulnerability