Protect yourself against future threats.
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2005.0580 -- Sun Alert Notification 101816 Security Vulnerabilities in the gzip(1) Command 22 July 2005 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: gzip Publisher: Sun Microsystems Operating System: Solaris 10 Solaris 9 Solaris 8 Impact: Create Arbitrary Files Increased Privileges Access: Existing Account CVE Names: CAN-2005-1228 CAN-2005-0988 Original Bulletin: http://sunsolve.sun.com/search/printfriendly.do?assetkey=1-26-101816-1 - --------------------------BEGIN INCLUDED TEXT-------------------- Sun(sm) Alert Notification * Sun Alert ID: 101816 * Synopsis: Security Vulnerabilities in the gzip(1) Command * Category: Security * Product: Solaris 9 Operating System, Solaris 10 Operating System, Solaris 8 Operating System * BugIDs: 6283819, 6294656 * Avoidance: Workaround * State: Workaround * Date Released: 20-Jul-2005 * Date Closed: * Date Modified: 1. Impact Security vulnerabilities in the gzip(1) command may result in one or both of the following issues: 1. An unprivileged local user may be able to change the permissions on another user's file if the targeted user is uncompressing a file in a directory which is writable by both users. This issue is referenced in the following document: * http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-0988 2. An unprivileged local user may be able to create arbitrary files on the system if they can induce another user to decompress a specially crafted gzip-compressed file using either the "-N" or "--name" options to gzip(1) or gunzip (see gzip(1)). The new files would only be created in directories which the user running gzip(1) has permission to write to. This issue is referenced in the following document: * http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-1228 2. Contributing Factors These issues can occur in the following releases: SPARC Platform * Solaris 8 * Solaris 9 * Solaris 10 x86 Platform * Solaris 8 * Solaris 9 * Solaris 10 Note: Solaris 7 does not contain the gzip(1) utility and is not affected by this issue. In order for the first issue described above to occur, the gzip(1) utility must be used to uncompress a file in a directory which is writable by other users and does not have the sticky bit set. To determine if the sticky bit is set on a directory, the following command can be used: $ ls -ld directory drwxr-xr-t 2 user group 512 Jul 7 16:38 directory/ If the "t" flag is indicated, as shown above, then the sticky bit is set. In order for the second issue described above to occur, the gzip(1) or gunzip (see gzip(1)) utility must be invoked with the "-N" or "--name" flag during decompression. 3. Symptoms If the first issue described above occurs, the output file created by the gzip(1) command will be a link to another file belonging to the user, rather than the expected file. The target file to which the new output file is linked will have its permissions changed to that of the original file being uncompressed. For example, if this issue occurred while a file with the following permissions: $ ls -l testfile.txt.gz -rw-r--r-- 1 localu nobody 42 Jul 11 16:53 testfile.txt.gz was being uncompressed using the following command: $ gzip -d testfile.txt.gz the output file, "testfile.txt" will be either a hard or a soft link instead of the expected output file. A hard link can be identified by using the "ls -l" command as shown below: $ ls -l testfile.txt -rw-r--r-- 2 localu nobody 11 Jul 11 16:53 testfile.txt If the file has a link count greater than 1, as in the output above (where the link count is 2), then the file is a hard link. The destination of a hard link can be found by locating other entries in the filesystem which have the same inode number, as in the example commands below: $ ls -i testfile.txt 192922 testfile.txt $ find /var/tmp -inum 192922 /var/tmp/shared-dir/cantread.txt /var/tmp/shared-dir/testfile.txt A soft link can be identified using the "file -h" command. If the file is a soft link, the output will be similar to the following: $ file -h testfile.txt testfile.txt: symbolic link to /var/tmp/shared-dir/cantread.txt If this issue occurrs, the destination of the hard or soft link will have had its permissions changed to those of the original gzip-compressed file: $ ls -l /var/tmp/shared-dir/cantread.txt -rw-r--r-- 2 localu nobody 11 Jul 11 16:53 /var/tmp/shared-dir/cantread. txt If the second issue described above occurs, the expected output file will not exist, and a new file will have been created on the system. If the the "-v" flag was passed to the gzip(1) utility while the compressed file was being decompressed, gzip(1) will have reported the names of any files created (the default behavior of gzip(1) is to delete the original file following decompression, so this cannot be done retrospectively). For example, if a compromised file was decompressed using the following command (in this case the '-v' flag is used, which highlights the file creation): $ gzip -vdN testfile.txt.gz testfile.txt.gz: -22.2% -- replaced with /tmp/testfile.txt the expected output file 'testfile.txt' will not exist: $ ls testfile.txt testfile.txt: No such file or directory and the new file "/tmp/testfile.txt" will have been created and will have contents determined by the author of the original compressed file: $ ls /tmp/testfile.txt /tmp/testfile.txt 4. Relief/Workaround The first issue described above can be avoided by setting the sticky bit on any shared directories in which the gzip(1) utility will be used. To set the sticky bit on a shared directory, use a command similar to the following: $ chmod +t shared_dir The permissions of a compromised file will be set to those of the archive being uncompressed, and therefore reducing the permissions of any gzip(1) archive before uncompressing it will prevent another user from gaining access to other files. For example, the following command could be run on a gzip(1) archive before uncompressing it, to ensure that only the owner of the file can read it: $ chmod 600 archive.gz The second issue described above can be avoided by not using the "-N" or "--name" flags when decompressing files with gzip(1) or gunzip. 5. Resolution A final resolution is pending completion. This Sun Alert notification is being provided to you on an "AS IS" basis. This Sun Alert notification may contain information provided by third parties. The issues described in this Sun Alert notification may or may not impact your system(s). Sun makes no representations, warranties, or guarantees as to the information contained herein. ANY AND ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT, ARE HEREBY DISCLAIMED. BY ACCESSING THIS DOCUMENT YOU ACKNOWLEDGE THAT SUN SHALL IN NO EVENT BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, PUNITIVE, OR CONSEQUENTIAL DAMAGES THAT ARISE OUT OF YOUR USE OR FAILURE TO USE THE INFORMATION CONTAINED HEREIN. This Sun Alert notification contains Sun proprietary and confidential information. It is being provided to you pursuant to the provisions of your agreement to purchase services from Sun, or, if you do not have such an agreement, the Sun.com Terms of Use. This Sun Alert notification may only be used for the purposes contemplated by these agreements. Copyright 2000-2005 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, CA 95054 U.S.A. All rights reserved - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. NOTE: Third Party Rights This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. The decision to follow or act on information or advice contained in this security bulletin is the responsibility of each user or organisation, and should be considered in accordance with your organisation's site policies and procedures. AusCERT takes no responsibility for consequences which may arise from following or acting on information or advice contained in this security bulletin. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the author's website to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. Previous advisories and external security bulletins can be retrieved from: http://www.auscert.org.au/render.html?cid=1980 If you believe that your computer system has been compromised or attacked in any way, we encourage you to let us know by completing the secure National IT Incident Reporting Form at: http://www.auscert.org.au/render.html?it=3192 =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane Qld 4072 Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iQCVAwUBQuA3Yih9+71yA2DNAQKjXAP/b5ZYuBTDpuelmr2DJGctfJ47lvCVt8jX 7xUQjywun10S3vPBSOE9/2FDRugzqtMNCxPPBSTiAsyXa8o19oWUwd5FyYjoaiHx Dt9Pu/1k2CFngUreoMjUO+5FgZMdkT7Z8M3jlOzjCyctVEgRfMGqx1nEsSqjzVTm W7Q/EYREDKI= =02Tm -----END PGP SIGNATURE-----