GNU Mailutils 0.6 mail header_get_field_name() Buffer Overflow
Vulnerability

iDEFENSE Security Advisory 05.25.05
http://www.idefense.com/application/poi/display?type=vulnerabilities
May 25, 2005

I. BACKGROUND

The GNU mailutils package is a collection of mail-related
utilities, including local and remote mailbox access services.
More information is available at the following site:

    http://www.gnu.org/software/mailutils/mailutils.html

II. DESCRIPTION

Exploitation of a buffer overflow vulnerability in the mail
binary of the GNU Projects Mailutils package may allow a remote
attacker to execute commands with the privileges of the
targeted user.

Due to a coding error in the library function
header_get_field_name() in mailbox/header.c, a buffer overflow
condition exists. The code below checks if the value of 'len' is
greater than the value of 'buflen', but always sets the value of
'len' to be the same, effectively performing no instruction.

      len = (len > buflen) ? len : len;

This code will set 'len' to the value of 'buflen' if 'len' is
greater than 'buflen'. This typo allows the buffer overflow to
occur. The code should be:

      len = (len > buflen) ? buflen : len;

III. ANALYSIS

Successful exploitation of the vulnerability would allow an
email sent by a remote user to cause a buffer overflow, allowing
execution of arbitrary commands in the context of the targeted
user. Access to a user account may allow further escalation of
privileges via local attacks.

IV. DETECTION

iDEFENSE Labs has verified the existence of this vulnerability
in versions 0.5 and 0.6 of the GNU Mailutils package. It is
suspected that any previous versions may also be affected.

It should be noted that the mail command from the GNU mailutils
package is NOT the default mail client on the vast majority of
Linux installations. The mailx mail client is by far much more
likely to be installed. The mailx mail client is typically
installed in /bin/mail, whereas the GNU mailutils mail client is
typically installed in /usr/bin/mail. These values are not
universal, and additional verification should be performed to
determine which version you have installed.

V. WORKAROUND

When possible, run client software as a regular user with
limited access to system resources. This may limit the immediate
consequences of client-side vulnerabilities.

VI. VENDOR RESPONSE

This vulnerability has been fixed in GNU mailutils 0.6.90 which is
available for download at:

   ftp://alpha.gnu.org/gnu/mailutils/

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2005-1520 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

05/12/2005  Initial vendor notification
05/12/2005  Initial vendor response
05/25/2005  Public disclosure

IX. CREDIT

infamous41md@hotpop.com is credited with the discovery of this
vulnerability.

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X. LEGAL NOTICES

Copyright (c) 2005 iDEFENSE, Inc.

Permission is granted for the redistribution of this alert
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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.