Exim is a mail transfer agent (MTA) for Unix systems similar to
sendmail. More information is available at the following URL:
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 dns_build_reverse() function. The
function fails to check the length of a string which it copies into a
fixed length buffer. This string is user controlled and passed into the
program from a command line option.
The following example demonstrates an input that will crash Exim:
/path/to/exim-binary -bh ::%A:::::::::::::::::`perl -e 'print pack("L",0xdeadbeef) x 256'`
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 email messages, or possibly further
iDEFENSE has confirmed the existence of this vulnerability in Exim
versions 4.40 and 4.41. A source audit of version 4.42 suggests that it
is also vulnerable. It is suspected that earlier versions are also
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 (http://cve.mitre.org), which standardizes names for
09/30/2004 Initial vendor notification
09/30/2004 Initial vendor response
01/14/2005 Public disclosure
The discoverer of this vulnerability wishes to remain anonymous.
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Copyright © 2004 Verisign, Inc.
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