Public Vulnerability Reports

Exim host_aton() Buffer Overflow Vulnerability



Exim is a message transfer agent developed for use on Unix systems. More
information is available at:


Local exploitation of a buffer overflow vulnerability in Exim 4.41 may
allow execution of arbitrary commands with elevated privileges.

The problem specifically exists in the host_aton function. The function
fails to check the number of elements it stores in a fixed size array.
The elements come from a user-controlled string and are passed into the
program from a command line option.


Exploitation of this vulnerability will give an attacker access to the
mailer uid. The exim mailer is setuid root, but drops privileges before
the vulnerable code is reached. Having the mailer uid may allow access
to sensitive information in e-mail messages or possibly further


Exim versions 4.40 and 4.41 have been confirmed vulnerable. The source
code for version 4.42 suggests that it is also vulnerable. It is
suspected that previous versions are vulnerable.


iDEFENSE is currently unaware of any effective workarounds for this


The vulnerability has been fixed in Exim release 4.44.


The Common Vulnerabilities and Exposures (CVE) project has assigned the
names CAN-2005-0021 to these issues. This is a candidate for inclusion
in the CVE list (, which standardizes names for
security problems.


12/23/2004   Initial vendor notification
12/29/2004   Initial vendor response
01/07/2005   Public disclosure


The discoverer of this vulnerability wishes to remain anonymous.

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Copyright © 2004 Verisign, Inc.

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at the time of publishing based on currently available information. Use
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