Multiple Vendor XMail 'sendmail' Recipient Buffer Overflow Vulnerability

iDEFENSE Security Advisory 10.13.05
www.idefense.com/application/poi/display?id=321&type=vulnerabilities
October 13, 2005

I. BACKGROUND

XMail is an Internet and intranet mail server. XMail sources compile
under GNU/Linux, FreeBSD, OpenBSD, NetBSD, OSX, Solaris and NT/2K/XP.

More information can be found at the vendor website:

   http://www.xmailserver.org/

II. DESCRIPTION

Local exploitation of a buffer overflow vulnerability in XMail, as
distributed with multiple vendors' operating systems, allows local
attackers to execute arbitrary code with elevated privileges.

The vulnerability exists because of insufficent bounds checking on
user-supplied data. Specifically, the AddressFromAtPtr function fails to
check bounds on arguments passed from other functions, and as a result
an exploitable stack overflow condition occurs when specifying the "-t"
command line option. The "-t" command line option allows users to
specify the recipient value in the text of the message on a line
beginning with "To:". XMail passes the user-supplied value without
bounds checking to AdressFromAtPtr and attempts to store the hostname
portion of the e-mail address in a 256-byte buffer. Crafted e-mail
addresses can overflow the buffer and overwrite stack process control
data, resulting in local code execution with elevated privileges.

III. ANALYSIS

Successful exploitation will result in code execution with elevated
privileges. XMail is distributed in RPM, DEB and source format. The RPM
distribution installs the sendmail binary with setuid root privileges.
Exploitation of XMail installed from RPM will yield root. Other
distribution formats install the sendmail binary as setgid mail.
Exploitation resulting in group mail privileges will allow an attacker
to read all unencrypted mail stored locally in the system mail folders.

IV. DETECTION

iDEFENSE Labs has confirmed the existence of this vulnerability in XMail
1.21.

V. WORKAROUND

As a workaround solution, local mail delivery can be restricted and a
standard mail user-agent may be used to talk to the XMail SMTP server.

VI. VENDOR RESPONSE

The vendor has released XMail 1.22 to address this issue which is
available for download at:

   http://www.xmailserver.org/

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2005-2943 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

10/12/2005  Initial vendor notification
10/12/2005  Initial vendor response
10/13/2005  Coordinated public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright (c) 2005 iDEFENSE, Inc.

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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.