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Message-ID: <FB24803D1DF2A34FA59FC157B77C970503C8ADF1@idserv04.idef.com> From: idlabs-advisories at idefense.com (idlabs-advisories@...fense.com) Subject: iDEFENSE Security Advisory [IDEF0731] Exim auth_spa_server() Buffer Overflow Vulnerability Exim auth_spa_server() Buffer Overflow Vulnerability iDEFENSE Security Advisory [IDEF0731] www.idefense.com/application/poi/display?id=178&type=vulnerabilities January 07, 2004 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 Remote exploitation of a buffer overflow vulnerability in Exim 4.41 may allow execution of arbitrary commands with elevated privileges. Exim is a message transfer agent developed for use on Unix systems. The problem specifically exists in the auth_spa_server function. The function fails to check the length of input to spa_base64_to_bits(), which decodes a Base64-encoded string into a buffer of a fixed length. This string is user-controlled and passed to the program from a remote connection. III. ANALYSIS Exploitation of this vulnerability will give an attacker remote access to the mailer uid. The exim mailer is setuid root, but drops privileges before the vulnerable code is reached. A remote attacker may be able to use other vulnerabilities to further elevate their privileges. This vulnerability is only exploitable when the spa authentication method has been configured by setting AUTH_SPA=yes in Local/Makefile when building it. IV. DETECTION Exim versions 4.40 and 4.41 have been confirmed vulnerable. The source code for version 4.42 suggests that it is vulnerable. It is suspected that previous versions are also vulnerable. To determine if the Exim version being used is vulnerable, connect to port 25 of the machine with Exim installed and type: EHLO localhost If AUTH NTLM appears in the output the application may be 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-2005-0022 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 01/07/2004 Coordinated 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@...fense.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.
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