GNU Mailutils 0.6 imap4d FETCH Command Resource Consumption DoS
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

Remote exploitation of an input validation in the FETCH command
of the imap4d server from the GNU Project's Mailutils package
error may allow an authenticated remote attacker to perform a
denial of service against an affected system.

The imap4d server allows remote users to retrieve their email
via the Internet Message Access Protocol, Version 4rev1 as
specified in RFC3501. This is a client/server protocol supported
by a large number of email clients on multiple platforms.

The vulnerability specifically exists in the handling of the
sequence range agument to the FETCH command. A sequence range
such as 1:4294967294 will cause the the spawned instance of the
server to enter what is effectively an infinite loop, allocating
memory on each cycle.

III. ANALYSIS

Successful exploitation of the vulnerability would allow a
remote authenticated used to cause the system hosting the imap4d
to become unresponsive due to lack of memory resources. On some
operating systems, such as Linux, processes will be killed by
the kernel out of memory manager.

IV. DETECTION

iDEFENSE Labs has verified the existance of this vulnerability
in versions 0.5 and 0.6 of the GNU Mailutils package. It is
suspected that any previous versions which contain the imap4d
server are also affected.

V. WORKAROUND

iDEFENSE is currently unaware of any effective workarounds for
this issue. Access to the affected host should be filtered at
the network boundary if global accessibility is not required.
Restricting access to only trusted hosts and networks may reduce
the likelihood of exploitation.

Applying resource limits on the memory avaialable to the imap4d
process will cause the spawned instance of the server to exit
when it reaches the limit. Information on how to to perform this
operation is operating system dependant, and may cause some
normal operations, especially on large messages, to fail.

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-2005-1522 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.

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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.