iDEFENSE Security Advisory 05.25.05: GNU Mailutils 0.6 imap4d FETCH Command Resource Consumption DoS Vulnerability

Type securityvulns
Reporter Securityvulns
Modified 2005-05-26T00:00:00


GNU Mailutils 0.6 imap4d FETCH Command Resource Consumption DoS Vulnerability

iDEFENSE Security Advisory 05.25.05 May 25, 2005


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:


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.


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.


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.


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.


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


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 (, which standardizes names for security problems.


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

IX. CREDIT is credited with the discovery of this vulnerability.

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Copyright (c) 2005 iDEFENSE, Inc.

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