Public Vulnerability Reports

Ipswitch IMail IMAP LSUB DoS Vulnerability



Ipswitch Collaboration Suite (ICS) is a comprehensive communication and
collaboration solution for Microsoft Windows with a customer base of
over 53 million users. More information is available on the vendor's


Remote exploitation of a denial of service (DoS) vulnerability in
Ipswitch Inc.'s IMail IMAP daemon allows attackers to cause 100 percent
CPU use on the server, thereby preventing legitimate users from
retrieving e-mail.

The problem specifically exists within IMAPD32.EXE upon parsing a
malformed LSUB command. An attacker can cause the daemon to produce
heavy load by transmitting a long string of NULL characters to the
'LSUB' IMAP directive. This, in turn, causes an infinite loop,
eventually exhausting all available system resources and causing a
denial of service.


Exploitation allows unauthenticated remote attackers to render the IMAP
server useless, thereby preventing legitimate users from retrieving e-
mail. This attack takes few resources to launch and can be repeated
to ensure that an unpatched system is unable to recover. Exploitation
requires a valid IMAP account, thus limiting the impact of this


iDEFENSE has confirmed the existence of this vulnerability in Ipswitch
IMail version 8.13. It is suspected that earlier versions are also


As this vulnerability is exploited after authentication occurs, ensuring
that only trusted users have accounts can mitigate the risk somwhat. As
a more effective workaround, consider limiting access to the IMAP server
by filtering TCP port 143. If possible, consider disabling IMAP and
forcing users to use POP3.


The vendor has released the following hotfix to fix this vulnerability
in IMail Server 8.15:

The vendor has released the following hotfix to fix this vulnerability
in IMail Server 8.2:
The vendor has released the following hotfix to fix this vulnerability
in Ipswitch Collaboration Suite 2.0:

The associated vendor advisories are available at:


The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2005-1249 to this issue. This is a candidate for inclusion in
the CVE list (, which standardizes names for
security problems.


04/25/2005   Initial vendor notification
05/10/2005   Initial vendor response
05/24/2005   Public disclosure


The discoverer of the first vulnerability wishes to remain anonymous.

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Copyright © 2005 Verisign, Inc.

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