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iDEFENSE Security Advisory 01.14.05: Exim dns_buld_reverse() Buffer Overflow Vulnerability

Exim dns_buld_reverse() Buffer Overflow Vulnerability iDEFENSE Security Advisory 01.14.05www.idefense.com/application/poi/display?id=183&type=vulnerabilitiesJanuary 14, 2005I. BACKGROUNDExim is a mail transfer agent (MTA) for Unix systems similar tosendmail. More information is available at the following URL:http://www.exim.org/II. DESCRIPTIONLocal 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. Thefunction 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. ANALYSISExploitation of this vulnerability will give an attacker access to the mailer uid. (The exim mailer is setuid root, but drops privileges beforethe vulnerable code is reached). Having the mailer uid may allow access to sensitive information in email messages, or possibly further elevation.IV. DETECTIONiDEFENSE 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. WORKAROUNDiDEFENSE is currently unaware of any effective workarounds for this vulnerability.VI. VENDOR RESPONSEA patch for Exim release 4.43 which addresses this vulnerability isavailable at:http://www.exim.org/mail-archives/exim-announce/2005/msg00000.htmlThe patch will be incorporated into a future Exim release (4.50).VII. CVE INFORMATIONA Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has notbeen assigned yet.VIII. DISCLOSURE TIMELINE09/30/2004  Initial vendor notification09/30/2004  Initial vendor response01/14/2005  Public disclosureIX. CREDITThe discoverer of this vulnerability wishes to remain anonymous.Get paid for vulnerability researchhttp://www.idefense.com/poi/teams/vcp.jspX. LEGAL NOTICESCopyright (c) 2004 iDEFENSE, Inc.Permission is granted for the redistribution of this alertelectronically. It may not be edited in any way without the expresswritten consent of iDEFENSE. If you wish to reprint the whole or anypart of this alert in any other medium other than electronically, pleaseemail customerservice () idefense com for permission.Disclaimer: The information in the advisory is believed to be accurateat the time of publishing based on currently available information. Useof the information constitutes acceptance for use in an AS IS condition.There are no warranties with regard to this information. Neither theauthor nor the publisher accepts any liability for any direct, indirect,or consequential loss or damage arising from use of, or reliance on,this information.

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