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AA-2003.01                     AUSCERT Advisory

                          Sendmail Vulnerability
                             28 February 2003
Last Revised: --

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AusCERT has received information that a vulnerability exists in all
versions of sendmail, an open source SMTP mail server.

This vulnerability may allow remote users to gain root privileges.

Exploit information involving this vulnerability may exist, but is
currently not in the public domain.

AusCERT recommends that sites take the steps outlined in section 3 as soon
as possible.

Updates to this advisory will be released as new information becomes
available.

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1.  Description

    Sendmail is an open source mail server program used for the routing
    and delivery of e-mail messages.  It is estimated that 75% of the
    Internet's e-mail traffic is handled by sendmail based servers.

    A buffer overflow in the header parsing of an e-mail message has been
    discovered in the open source and commercial product lines of the
    sendmail SMTP mail server.  All versions of sendmail prior to 8.12.8
    on all platforms are vulnerable.

    A carefully designed e-mail message will allow an attacker to execute
    arbitrary code on the mail server with the privileges of the sendmail
    daemon, typically root.

    It is important to note that such a designed message may pass through
    non-sendmail based servers unaffected, and will exploit the first
    vulnerable sendmail server encountered.  This may put a sendmail server
    which is internal to an organisation at risk, even if other mail server
    software is used at the network border.

    Successful exploitation of this vulnerability will not generate any
    log entries on the server.

    The Sendmail Consortium have released patches for sendmail versions
    8.9, 8.10, 8.11, and 8.12.  Sendmail based servers prior to 8.9
    must first be upgraded in order for the patches to be applicable.

2.  Impact

    This vulnerability may allow remote users to gain root privileges.
    Due to the nature of this vulnerability, firewalls and/or packet
    filters are not able to protect vulnerable mail servers.

3.  Workarounds/Mitigation

    AusCERT recommends that sites prevent the exploitation of the
    vulnerability in sendmail by immediately upgrading to version 8.12.8
    or applying the patches for 8.9.x, 8.10.x, 8.11.x, and 8.12.x

    Sendmail 8.12.8 and associated patches may be downloaded directly from
    the sendmail FTP server at:

        ftp.sendmail.org/pub/sendmail

    For instructions on applying the patches for specific versions of
    sendmail, please see:

        http://www.sendmail.org/patchcr.html

    While there is no known workaround to this vulnerability, you can help
    mitigate the impact until patches can be applied by setting the
    RunAsUser option in the sendmail configuration.  This also promotes the
    best practice of running applications with the least privileges
    required whenever possible.

    Common protection mechanisms such as the use of non-executable stacks
    do not offer any protection from exploitation of this vulnerability.
    
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AusCERT has made every effort to ensure that the information contained
in this document is accurate.  However, the decision to use the information
described is the responsibility of each user or organisation.  The
appropriateness of this document for an organisation or individual system
should be considered before application in conjunction with local policies
and procedures.  AusCERT takes no responsibility for the consequences of
applying the contents of this document.

If you believe that your system has been compromised, contact AusCERT or
your representative in FIRST (Forum of Incident Response and Security
Teams).

AusCERT also maintains a World Wide Web service which is found on:
http://www.auscert.org.au.

Internet Email: auscert@auscert.org.au
Facsimile:      (07) 3365 7031
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AusCERT personnel answer during Queensland business
                hours which are GMT+10:00 (AEST).  On call after hours
                for member emergencies only.

Postal:
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld  4072
AUSTRALIA


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Revision History


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