Exim host_aton() Buffer Overflow Vulnerability iDEFENSE Security Advisory [IDEF0725] http://www.idefense.com/application/poi/display?type=vulnerabilities January 07, 2005 I. BACKGROUND Exim is a message transfer agent developed for use on Unix systems. More information is available at: 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 host_aton function. The function fails to check the number of elements it stores in a fixed size array. The elements come from a user-controlled string and are passed into the program from a command line option. 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 e-mail messages or possibly further elevation. IV. DETECTION Exim versions 4.40 and 4.41 have been confirmed vulnerable. The source code for version 4.42 suggests that it is also vulnerable. It is suspected that previous versions are 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 The Common Vulnerabilities and Exposures (CVE) project has assigned the names CAN-2005-0021 to these issues. This is a candidate for inclusion in the CVE list (http://cve.mitre.org), which standardizes names for security problems. VIII. DISCLOSURE TIMELINE 12/23/2004 Initial vendor notification 12/29/2004 Initial vendor response 01/07/2005 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@idefense.com 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.