__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Korn Shell (ksh) suid_exec Vulnerability April 8, 1998 23:00 GMT Number H-15a ______________________________________________________________________________ PROBLEM: A problem has been identified in the "suid_exec" program often supplied with the Korn Shell (ksh) distribution. PLATFORM: All operating systems with "suid_exec" program supplied with the Korn Shell (ksh) distribution. DAMAGE: Local users may gain root privileges. SOLUTION: Apply the workaround described below. ______________________________________________________________________________ VULNERABILITY Exploit details involving this vulnerability have been widely ASSESSMENT: distributed. ______________________________________________________________________________ [ Appended on April 8, 1998 with additional vendor information ] [ Start AUSCERT Advisory ] =========================================================================== AA-96.17 AUSCERT Advisory Korn Shell (ksh) suid_exec Vulnerability 5 December 1996 Last Revised: -- ---------------------------------------------------------------------------- AUSCERT has received information that there is a vulnerability in the "suid_exec" program often supplied with the Korn Shell (ksh) distribution. ksh may be part of the standard vendor distribution or may have been installed as additional software by system administrators. This vulnerability may allow local users to gain root privileges. Exploit details involving this vulnerability have been widely distributed. At this stage, AUSCERT is unaware of any official vendor patches. AUSCERT recommends that sites apply the workaround given in Section 3 until vendor patches are made available. This advisory will be updated as new information becomes available. ---------------------------------------------------------------------------- 1. Description suid_exec is a program that is often installed when the Korn shell (ksh) interpreter is installed. suid_exec is installed to allow the execution of setuid/setgid shell scripts and shell scripts which do not have read permissions set. All versions of suid_exec are currently vulnerable. The vulnerability in suid_exec may allow arbitrary commands to be executed with root privileges. Exploit information involving this vulnerability has been made publicly available. suid_exec is known to be present in the default installation on the following Unix operating systems: IRIX 5.x IRIX 6.x This list is not necessarily complete, and other operating systems may have suid_exec installed by default. Sites may also have installed suid_exec when installing the publicly available version of the Korn Shell (ksh). This version of suid_exec is also vulnerable. All sites are encouraged to check their systems for the presence of the suid_exec program. By default, suid_exec will be found in /etc. To determine the location of any other copies of suid_exec, the following command can be executed as root: # find / -name suid_exec -perm -4000 -exec ls -l {} \; If suid_exec is installed, sites should take the steps outlined in Section 3. 2. Impact Local users may gain root privileges. 3. Workarounds/Solution AUSCERT recommends that sites prevent the exploitation of the vulnerability in suid_exec by immediately applying the workaround given in Section 3.1. Currently there are no vendor patches available that address this vulnerability. AUSCERT recommends that official vendor patches be installed when they are made available. 3.1 Remove setuid and execute permissions Until official vendor patches are made available, sites should remove the setuid root and execute permissions from suid_exec. For example, if suid_exec is located in /etc, the following command should be run as root: # chmod 400 /etc/suid_exec # ls -l /etc/suid_exec -r-------- 1 root sys 14384 May 30 1996 /etc/suid_exec Note that the removing these permissions from suid_exec may stop non-root users from executing setuid/setgid shell scripts and scripts upon which read permissions have not been set. 4. Additional measures Most Unix systems ship with numerous programs which have setuid or setgid privileges. Often the functionality supplied by these privileged programs is not required by many sites. The large number of privileged programs that are shipped by default are to cater for all possible uses of the system. AUSCERT encourages sites to examine all the setuid/setgid programs and determine the necessity of each program. If a program does not absolutely require the setuid/setgid privileges to operate (for example, it is only run by the root user), the setuid/setgid privileges should be removed. Furthermore, if a program is not required at your site, then all execute permissions should be removed. A sample command to find all setuid/setgid programs is (run as root): # find / \( -perm -4000 -o -perm -2000 \) -exec ls -ld {} \; It is AUSCERT's experience that many vulnerabilities are being discovered in setuid/setgid programs which are not necessary for the correct operation of most systems. Sites can increase their security by removing unnecessary setuid/setgid programs. For example, the functionality provided by the suid_exec program is not needed by most sites. If sites had previously disabled the suid_exec program, they would not have been vulnerable to this latest exploit. ---------------------------------------------------------------------------- AUSCERT thanks Silicon Graphics Inc. for their assistance and technical expertise essential for the production of this advisory. ---------------------------------------------------------------------------- [ End AUSCERT Advisory ] [ Append with Silicon Graphics Inc. Advisory ] -----BEGIN PGP SIGNED MESSAGE----- ______________________________________________________________________________ Silicon Graphics Inc. Security Advisory Title: suid_exec Buffer Overflow Title: AUSCERT AA-96.17 Number: 19980405-01-I Date: April 6, 1998 ______________________________________________________________________________ Silicon Graphics provides this information freely to the SGI user community for its consideration, interpretation, implementation and use. Silicon Graphics recommends that this information be acted upon as soon as possible. Silicon Graphics provides the information in this Security Advisory on an "AS-IS" basis only, and disclaims all warranties with respect thereto, express, implied or otherwise, including, without limitation, any warranty of merchantability or fitness for a particular purpose. In no event shall Silicon Graphics be liable for any loss of profits, loss of business, loss of data or for any indirect, special, exemplary, incidental or consequential damages of any kind arising from your use of, failure to use or improper use of any of the instructions or information in this Security Advisory. ______________________________________________________________________________ - ----------------------- - --- Issue Specifics --- - ----------------------- The suid_exec program is part of the Korn Shell (ksh) software distributions. Under normal operation, the suid_exec program will run shell scripts setuid. Unfortunately, a buffer overrun has been discovered in the suid_exec program which could allow arbitrary commands to be run as the privileged user root. Silicon Graphics Inc. has investigated the issue and recommends the following steps for neutralizing the exposure. It is HIGHLY RECOMMENDED that these measures be implemented on ALL vulnerable SGI systems. - -------------- - --- Impact --- - -------------- The suid_exec program is installed by default on all IRIX 5.x and 6.x systems. With a local account, the suid_exec buffer overrun vulnerability can be exploited locally and remotely. The suid_exec buffer overrun vulnerability can be utilized to execute commands with root privileges. The suid_exec buffer overrun vulnerability has been publicly discussed in Usenet newsgroups and mailing lists and also reported in AUSCERT Security Advisory AA-96.17. - -------------------------- - --- Temporary Solution --- - -------------------------- To disable the programs that are believed to be vulnerable, use the following steps. 1) Become the root user on the system. % /bin/su - Password: # 2) Change the setuid root permissions on the program. # /bin/chmod 400 /sbin/suid_exec ************ *** NOTE *** ************ Removing these permissions from suid_exec will stop non-root users from executing setuid/setgid shell scripts and scripts upon which read permissions have not been set. 3) Confirm the new permissions on the program. # ls -la /sbin/suid_exec -r-------- 1 root sys 14384 May 30 1996 /sbin/suid_exec 4) Using the find command, locate any additional copies of suid_exec and disable them. Note that this is one long command, though we have separated it onto two lines using backslashes. # find / -local -type f -name suid_exec \ -print -ok chmod 400 '{}' \; This command will find all files on a system that are - only in the local file system you name (/ -local) - regular files (-type f) - named appropriately (-name suid_exec) Once found, those files will - have their names printed (-print) - have their modes changed, but only if you type `y' in response to the prompt (-ok chmod 400 '{}' \;) 5) Return to previous level. # exit $ - ---------------- - --- Solution --- - ---------------- The suid_exec program is considered freeware and will not be patched. As freeware software, all reasonable efforts will be made to address the issue in future versions of the software. OS Version Vulnerable? Patch # Other Actions ---------- ----------- ------- ------------- IRIX 3.x no IRIX 4.x no IRIX 5.0.x yes not avail Note 1 IRIX 5.1.x yes not avail Note 1 IRIX 5.2 yes not avail Note 1 IRIX 5.3 yes not avail Note 1 IRIX 6.0.x yes not avail Note 1 IRIX 6.1 yes not avail Note 1 IRIX 6.2 yes not avail Note 1 IRIX 6.3 yes not avail Note 1 IRIX 6.4 yes not avail Note 1 Notes: 1) Freeware upgrades should be applied. - ------------------------ - --- Acknowledgments --- - ------------------------ Silicon Graphics wishes to thank AUSCERT for their assistance in this matter. - ----------------------------------------------------------- - --- Silicon Graphics Inc. Security Information/Contacts --- - ----------------------------------------------------------- If there are questions about this document, email can be sent to cse-security-alert@sgi.com. ------oOo------ Silicon Graphics provides security information and patches for use by the entire SGI community. This information is freely available to any person needing the information and is available via anonymous FTP and the Web. The primary SGI anonymous FTP site for security information and patches is sgigate.sgi.com (204.94.209.1). Security information and patches are located under the directories ~ftp/security and ~ftp/patches, respectively. The Silicon Graphics Security Headquarters Web page is accessible at the URL http://www.sgi.com/Support/security/security.html. For issues with the patches on the FTP sites, email can be sent to cse-security-alert@sgi.com. For assistance obtaining or working with security patches, please contact your SGI support provider. ------oOo------ Silicon Graphics provides a free security mailing list service called wiretap and encourages interested parties to self-subscribe to receive (via email) all SGI Security Advisories when they are released. Subscribing to the mailing list can be done via the Web (http://www.sgi.com/Support/security/wiretap.html) or by sending email to SGI as outlined below. % mail wiretap-request@sgi.com subscribe wiretap end ^d In the example above, is the email address that you wish the mailing list information sent to. The word end must be on a separate line to indicate the end of the body of the message. The control-d (^d) is used to indicate to the mail program that you are finished composing the mail message. ------oOo------ Silicon Graphics provides a comprehensive customer World Wide Web site. This site is located at http://www.sgi.com/Support/security/security.html. ------oOo------ For reporting *NEW* SGI security issues, email can be sent to security-alert@sgi.com or contact your SGI support provider. A support contract is not required for submitting a security report. ______________________________________________________________________________ This information is provided freely to all interested parties and may be redistributed provided that it is not altered in any way, Silicon Graphics is appropriately credited and the document retains and includes its valid PGP signature. -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBNSlQ6LQ4cFApAP75AQEK/QP/QtoOa7kml2Rs2KgW2cx5s83SDXe6kXgD yqlIQUk7ZDbNEq7ha+3dezQG4V8VrJj2xaBmjNvdIky2NM7SNQbo8/Q4vwsXOG4W qfUhPgqaTZ4vqqh+hWQ009h8bAbU5VQiyeFqwrhOhs9eK56pVx9jKD/RZFB2g8uK wHeierfHt3M= =OPMG -----END PGP SIGNATURE----- [ End Silicon Graphics Inc. Advisory ] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of AUSCERT 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: +1 510-422-8193 FAX: +1 510-423-8002 STU-III: +1 510-423-2604 E-mail: ciac@llnl.gov For emergencies and off-hour assistance, DOE, DOE contractor sites, and the NIH may contact CIAC 24-hours a day. During off hours (5PM - 8AM PST), call the CIAC voice number 510-422-8193 and leave a message, or call 800-759-7243 (800-SKY-PAGE) to send a Sky Page. CIAC has two Sky Page PIN numbers, the primary PIN number, 8550070, is for the CIAC duty person, and the secondary PIN number, 8550074 is for the CIAC Project Leader. Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. World Wide Web: http://ciac.llnl.gov/ Anonymous FTP: ciac.llnl.gov (128.115.19.53) 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 ListProcessor, which ignores E-mail header subject lines. To subscribe (add yourself) to one of our mailing lists, send the following request as the E-mail message body, substituting CIAC-BULLETIN, CIAC-NOTES, SPI-ANNOUNCE or SPI-NOTES for list-name and valid information for LastName FirstName and PhoneNumber when sending E-mail to ciac-listproc@llnl.gov: subscribe list-name LastName, FirstName PhoneNumber e.g., subscribe ciac-notes OHara, Scarlett W. 404-555-1212 x36 You will receive an acknowledgment containing address, initial PIN, and information on how to change either of them, cancel your subscription, or get help. 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) H-04: HP-UX Ping Vulnerability H-05: Internet Hoaxes H-07: Sendmail SIGHUP-smtpd Vulnerability H-08: lpr Buffer Overrun Vulnerability H-09: HP 9000 Access Vulnerability H-10: HP-UX Security Vulnerabilities (passwd, fpkg2swpkg, newgrp) H-11: sendmail Group Permissions Vulnerability H-12: IBM AIX(r) 'SYN Flood' and 'Ping o' Death' Vulnerabilities H-13: IBM AIX(r) Security Vulnerabilities (gethostbyname, lquerypv) H-14: SGI IRIX Vulnerabilities (systour, OutOfBox, cdplayer, datman) RECENT CIAC NOTES ISSUED (Previous Notes available from CIAC) Notes 07 - 3/29/95 A comprehensive review of SATAN Notes 08 - 4/4/95 A Courtney update Notes 09 - 4/24/95 More on the "Good Times" virus urban legend Notes 10 - 6/16/95 PKZ300B Trojan, Logdaemon/FreeBSD, vulnerability in S/Key, EBOLA Virus Hoax, and Caibua Virus Notes 11 - 7/31/95 Virus Update, Hats Off to Administrators, America On-Line Virus Scare, SPI 3.2.2 Released, The Die_Hard Virus Notes 12 - 9/12/95 Securely configuring Public Telnet Services, X Windows, beta release of Merlin, Microsoft Word Macro Viruses, Allegations of Inappropriate Data Collection in Win95 Notes 96-01 - 3/18/96 Java and JavaScript Vulnerabilities, FIRST Conference Announcement, Security and Web Search Engines, Microsoft Word Macro Virus Update