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

From: customer service mailbox (customerservice_at_idefense.com)
Date: 01/14/05

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    Date: Fri, 14 Jan 2005 12:45:28 -0500
    To: <bugtraq@securityfocus.com>, <vulnwatch@vulnwatch.org>
    
    

    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@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.


  • Next message: Derek Martin: "Re: rssh and scponly arbitrary command execution"

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