Exim dns_buld_reverse() Buffer Overflow Vulnerability iDEFENSE Security Advisory 01.14.05 www.idefense.com/application/poi/display?id=183&type=vulnerabilities January 14, 2005 I. BACKGROUND Exim is a mail transfer agent (MTA) for Unix systems similar to sendmail. More information is available at the following URL: http://www.exim.org/ II. DESCRIPTION Local exploitation of a buffer overflow vulnerability in Exim 4.41 may allow execution of arbitrary commands with elevated privileges. The problem specifically exists in the dns_build_reverse() function. The function fails to check the length of a string which it copies into a fixed length buffer. This string is user controlled and passed into the program from a command line option. The following example demonstrates an input that will crash Exim: /usr/bin/exim -bh ::%A`perl -e 'print pack('L',0xdeadbeef') x 256'` III. ANALYSIS Exploitation of this vulnerability will give an attacker access to the mailer uid. (The exim mailer is setuid root, but drops privileges before the vulnerable code is reached). Having the mailer uid may allow access to sensitive information in email messages, or possibly further elevation. IV. DETECTION iDEFENSE has confirmed the existence of this vulnerability in Exim versions 4.40 and 4.41. A source audit of version 4.42 suggests that it is also vulnerable. It is suspected that earlier versions are also vulnerable. V. WORKAROUND iDEFENSE is currently unaware of any effective workarounds for this vulnerability. VI. VENDOR RESPONSE A patch for Exim release 4.43 which addresses this vulnerability is available at: http://www.exim.org/mail-archives/exim-announce/2005/msg00000.html The patch will be incorporated into a future Exim release (4.50). VII. CVE INFORMATION A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not been assigned yet. VIII. DISCLOSURE TIMELINE 09/30/2004 Initial vendor notification 09/30/2004 Initial vendor response 01/14/2005 Public disclosure IX. CREDIT The discoverer of this vulnerability wishes to remain anonymous. Get paid for vulnerability research http://www.idefense.com/poi/teams/vcp.jsp X. LEGAL NOTICES Copyright (c) 2004 iDEFENSE, Inc. Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDEFENSE. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please email customerservice@xxxxxxxxxxxx for permission. Disclaimer: The information in the advisory is believed to be accurate at the time of publishing based on currently available information. Use of the information constitutes acceptance for use in an AS IS condition. There are no warranties with regard to this information. Neither the author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information.
