[原文]The IMAP daemon (IMAPD32.EXE) in Ipswitch Collaboration Suite (ICS) allows remote attackers to cause a denial of service (CPU consumption) via an LSUB command with a large number of null characters, which causes an infinite loop.
iDEFENSE Security Advisory 05.24.05-2 - Remote exploitation of a denial of service (DoS) vulnerability in Ipswitch Inc.'s 8.13 IMail IMAP daemon allows attackers to cause 100 percent CPU use on the server, thereby preventing legitimate users from retrieving e-mail.
Ipswitch IMail IMAP LSUB DoS Vulnerability
iDEFENSE Security Advisory 05.24.05
May 24, 2005
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
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.
VI. VENDOR RESPONSE
The vendor has released the following patch to fix this vulnerability:
The associated vendor advisory can be found at:
VII. CVE INFORMATION
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 (http://cve.mitre.org), which standardizes names for
VIII. DISCLOSURE TIMELINE
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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X. LEGAL NOTICES
Copyright (c) 2005 iDEFENSE, Inc.
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at the time of publishing based on currently available information. Use
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Ipswitch IMail IMAP Daemon Malformed LSUB Command Remote DoS
Remote / Network Access
Denial of Service
Loss of Availability
IMail Server contains a flaw that may allow a remote denial of service. The issue is due to the IMAP daemon (IMAPD32.EXE) service while parsing malformed LSUB commands. By passing an overly long string of NULL characters to the 'LSUB' command, a remote attacker can cause the daemon to go into an infinite loop and consume all available CPU resources resulting in a loss of availability for the IMAP service.
Upgrade to version 8.2 Hotfix 2 or higher, as it has been reported to fix this vulnerability. An upgrade is required as there are no known workarounds.