__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Center ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN AIX libi18n Library Vulnerability July 24, 2001 15:00 GMT Number L-123 ______________________________________________________________________________ PROBLEM: There is a software vulnerability in the libi18n Library PLATFORM: IBM AIX 4.3.x and 5.1 NOTE: Fix will not be provided for versions prior to 4.3 as these are no longer supported by IBM. Affected customers are urged to upgrade to 4.3.3 at the latest maintenance level or to 5.1. DAMAGE: The "libi18n" library contains a function that is vulnerable to a buffer overflow through the LANG environment variable. Through the usage of the "LANG" environment variable a local user can obtain root level privileges. SOLUTION: Apply the temporary fix or workaround as specified by IBM. IBM is working on a official patch. Read the instructions regarding the 'efix' installation carefully before installing the temporary fix. ______________________________________________________________________________ VULNERABILITY The risk is LOW. There have been no publicly reported attacks ASSESSMENT: using this methodology and the usage requires local access. ______________________________________________________________________________ LINKS: PATCHES: ftp://aix.software.ibm.com/aix/efixes/security/libi18n_efix.tar.Z ______________________________________________________________________________ [****** Begin IBM advisory ******] IBM Global Services Managed Security Services Outside Advisory Redistribution 18 JUL 2001 23:47 GMT MSS-OAR-E01-2001:271.1 =========================================================================== The MSS Outside Advisory Redistribution is designed to provide customers of IBM Managed Security Services with access to the security advisories sent out by other computer security incident response teams, vendors, and other groups concerned about security. IBM makes no representations and assumes no responsibility for the contents or accuracy of the advisories themselves. IBM MSS is forwarding the following information from IBM. Contact information for IBM is included in the forwarded text below. Please contact them if you have any questions or need further information. =========================================================================== ----------- Forwarded Information Starts Here. -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 IBM SECURITY ADVISORY Thu Jun 28 10:06:00 CDT 2001 =========================================================================== VULNERABILITY SUMMARY VULNERABILITY: Buffer Overflow Vulnerability in libi18n Library PLATFORMS: IBM AIX 4.3.x and 5.1 SOLUTION: Apply the emergency-fixes described below, or employ the workaround, also described below. THREAT: Malicious local user could obtain root privileges. CERT Advisory: NONE. CVE candidate: CAN-2001-0533 =========================================================================== DETAILED INFORMATION I. Description AIX ships with the library "libi18n" located in the "/usr/ccs/lib" directory. This library contains a function that is vulnerable to a buffer overflow through the LANG environment variable. An ordinary user has the ability to set the "LANG" environment variable to any value they choose. When this variable is set to a suitably formatted string and a program is run which uses the vulnerable library, the program will terminate abnormally. If this program is also setuid root, aixterm for example, a malicious user has an opportunity to spawn a root shell and gain control of the machine. II. Impact A malicious local user can use a well-crafted exploit code to gain root privileges on the attacked system, compromising the integrity of the system and its attached local network. III. Solutions A. WORKAROUND If you do not wish to install the efix for this vulnerability but instead wait for the APAR that fixes it to be made available, you can also negate this vulnerability by making the "aixterm" program to be non-SUID. You must be "root" to do this. Ordinary users will still be able to use the program, although there may be unexpected side effects. B. Official Fix IBM is working on the following fixes which will be available soon: AIX 4.3.x - IY20867 AIX 5.1.0 - IY21309 NOTE: Fix will not be provided for versions prior to 4.3 as these are no longer supported by IBM. Affected customers are urged to upgrade to 4.3.3 at the latest maintenance level, or to 5.1. C. How to minimize the vulnerability Temporary fixes for AIX 4.3.x and 5.1 systems are available. The temporary fixes can be downloaded via ftp from: ftp://aix.software.ibm.com/aix/efixes/security/libi18n_efix.tar.Z The efix tarball consists of a patched libi18n tarred binary which is compatible with both 4.3.x and 5.1.0 releases. A copy of this Advisory is included in the efix tarball. These temporary fixes have not been fully regression tested; thus, IBM does not warrant the fully correct functioning of the efix. Customers install the efix and operate the modified version of AIX at their own risk. To proceed with efix installation: First, verify the MD5 cryptographic hash sums of each efix files you obtain from unpacking the efix tarball with those given below. These should match exactly; if they do not, double check the hash results and the download site address. If OK, contact IBM AIX Security at security-alert@austin.ibm.com and describe the discrepancy. Filename sum md5 ================================================================= libi18n.tar 34706 130 1227c815533ae2f70a0eac71c5016263 Efix Installation Instructions: ------------------------------- IMPORTANT NOTICE: Before installing the efix, you must upgrade to the latest maintenance level of AIX for your version of AIX. 1. Become root, if not already done. 2. Change to the /usr/ccs/lib directory. Make a backup copy of the existing libi18n.a binary, giving it a distinctive, meaningful name, such as "libi18n.a.original" or "libi18n.a.backup". This is IMPORTANT to do, so you can recover the original libi18n.a binary if something goes wrong during the installation of the efix! 3. In the root ("/") directory, download, uncompress, and untar the efix. a. uncompress libi18n_efix.tar.Z b. tar -xvf libi18n_efix.tar 4. You will have a tarfiles named "libi18n.tar". You may discard the other, unneeded tarfile. Untar the tarfile by executing "tar -xvf libi18n.tar". The efix version of libi18n will be untarred and placed in the proper directory. 5. Check to be certain that the new libi18n.a library is assigned proper permissions, "-r--r--r--", and the ownership is assigned properly, "bin" and "bin". IV. Obtaining Fixes IBM AIX APARs may be ordered using Electronic Fix Distribution (via the FixDist program), or from the IBM Support Center. For more information on FixDist, and to obtain fixes via the Internet, please reference http://techsupport.services.ibm.com/rs6k/fixes.html or send email to "aixserv@austin.ibm.com" with the word "FixDist" in the "Subject:" line. To facilitate ease of ordering all security related APARs for each AIX release, security fixes are periodically bundled into a cumulative APAR. For more information on these cumulative APARs including last update and list of individual fixes, send email to "aixserv@austin.ibm.com" with the word "subscribe Security_APARs" in the "Subject:" line. V. Acknowledgments Many thanks go to Troy Bollinger of IBM MSSD for discovering this vulnerability and for demonstrating its exploitation. VI. Contact Information Comments regarding the content of this announcement can be directed to: security-alert@austin.ibm.com To request the PGP public key that can be used to encrypt new AIX security vulnerabilities, send email to security-alert@austin.ibm.com with a subject of "get key". If you would like to subscribe to the AIX security newsletter, send a note to aixserv@austin.ibm.com with a subject of "subscribe Security". To cancel your subscription, use a subject of "unsubscribe Security". To see a list of other available subscriptions, use a subject of "help". IBM and AIX are a registered trademark of International Business Machines Corporation. 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