13 September 2006
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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2006.0661 -- [UNIX/Linux] Multiple Vendor X Server CID-keyed Fonts 'CIDAFM()' Integer Overflow 14 September 2006 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: XFree86 X.Org Publisher: iDEFENSE Operating System: UNIX variants (UNIX, Linux, OSX) Impact: Root Compromise Execute Arbitrary Code/Commands Access: Existing Account CVE Names: CVE-2006-3740 Original Bulletin: http://www.idefense.com/intelligence/vulnerabilities/display.php?id=412 - --------------------------BEGIN INCLUDED TEXT-------------------- Multiple Vendor X Server CID-keyed Fonts 'CIDAFM()' Integer Overflow Vulnerability iDefense Security Advisory 09.12.06 http://www.idefense.com/intelligence/vulnerabilities/ Sep 12, 2006 I. BACKGROUND The X Window System is a graphical windowing system based on a client/server model. More information about about The X Window system is available at the following link: http://en.wikipedia.org/wiki/X_Window_System II. DESCRIPTION Local exploitation of an integer overflow vulnerability in the 'CIDAFM()' function in the X.Org and XFree86 X server could allow an attacker to execute arbitrary code with privileges of the X server, typically root. The vulnerability specifically exists in the 'CIDAFM()' function of the code responsible for handling AFM (Adobe Font Metrics) files. The number of character metrics is obtained from the "StartCharMetrics" line of an AFM file and that value is then multiplied by the size of a single character metric record in order to calculate the space required to store the metrics. If the result of the multiplication is larger than the largest value that can be held in an integer, the amount actually allocated will be much smaller. Following this, the function attempts to read as many metric records as were specified on the line into that memory. As the contents of the file can be specified by a local user, and as the function will stop reading if an error is detected in the input, a controlled heap overflow may occur which may allow the execution of arbitrary code. III. ANALYSIS Successful local exploitation allows an attacker to execute arbitrary code as the root user. In order to exploit this vulnerability an attacker would require the ability to send commands to an affected X server. This typically requires access to the console, or access to the same account as a user who is on the console. One method of gaining the required access would be to remotely exploit a vulnerability in, for example, a graphical web browser. This would then allow an attacker to exploit this vulnerability and elevate their privileges to root. IV. DETECTION iDefense has confirmed the existence of this vulnerability in the X.org server version 6.8.2. Analysis of the source code for the current versions of the X.org and XFree86 servers indicates that current versions of both are vulnerable. Previous versions may also be affected. V. WORKAROUND Access to the vulnerable code can be prevented by removing the entry for the Type1 font module from your Xservers configuration file, often stored in /etc/X11 and named xorg.conf or XF86Config-4. To do this, remove the following line from the 'Module' section: Load "type1" This will prevent Type 1 fonts from loading, which may affect the appearance or operation of some applications. VI. VENDOR RESPONSE The X.Org foundation has addressed this vulnerability with libXfont version 1.2.1. Additionally, patches have been made available for older releases. " The XFree86 Project Inc. is making available a source patch available at ftp://xfree86.org/pub/XFree86/4.6.0/fixes/fix-01 that, in part, addresses this vulnerability. " VII. CVE INFORMATION The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2006-3740 to this issue. This is a candidate for inclusion in the CVE list (http://cve.mitre.org), which standardizes names for security problems. VIII. DISCLOSURE TIMELINE 08/25/2006 Initial vendor notification 08/25/2005 Initial vendor response (X.Org) 09/10/2006 Initial vendor response (XFree86) 09/12/2006 Coordinated public disclosure IX. CREDIT The discoverer of this vulnerability wishes to remain anonymous. Get paid for vulnerability research http://www.idefense.com/methodology/vulnerability/vcp.php Free tools, research and upcoming events http://labs.idefense.com/ X. LEGAL NOTICES Copyright Â© 2006 iDefense, Inc. Permission is granted for the redistribution of this alert electronically. 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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: email@example.com 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 iQCVAwUBRQjemih9+71yA2DNAQLQ9gP8Cjsl9K/hrCC/PsyqvxAqO5/PPRFuENOJ Xr8F+b7kUQnQP1cEnlqSz5gBSenfHpfGyH7Yh/27RveBFJPPgW2KzfBYg1tH7Ydh A1b2SflOVzOE2RPnkxT6vln5HVTrHXoFvhCemOF0kDzReJF9RD0d9BEC+ZLxfX/X nTs5IQtJyr8= =Dd9v -----END PGP SIGNATURE-----