The following message from Bugtraq, although discussing ZoneAlarm
MailSafe also applies to the regular expressions used in Sanitizer
configuration files. Basically, it's very easy to bypass
filename-based filtering rules in many mail filtering products by
simply appending a dot to all attachment names - the dot will be
ignored by Windows.
This particular exploit is so simple I rather expect virus/worm
writers will put it to use relatively quickly.
The solution is to simply add \.? to the end of all extension-matching
regular expressions, before the $. Example:
file_list_1 = (?i)(\.([0-9a-z_]{2,4}\.(com|exe|pif|lnk|bat|sc[rt]|vb[se]?))
file_list_1 += |(ants3set|wtc|readme|sslpatch)\.exe)$
Becomes:
file_list_1 = (?i)(\.([0-9a-z_]{2,4}\.(com|exe|pif|lnk|bat|sc[rt]|vb[se]?))
file_list_1 += |(ants3set|wtc|readme|sslpatch)\.exe)\.?$
----- Forwarded message from Edvice Security Services <38959@xyz.molar.is> -----
From: "Edvice Security Services" <38959@xyz.molar.is>
To: <39005@xyz.molar.is>
Subject: [bugtraq] Various Vulnerabilities in ZoneAlarm MailSafe
Date: Tue, 2 Apr 2002 10:33:13 +0200
X-Mailer: Microsoft Outlook, Build 10.0.2627
Tuesday April 2, 2002
Various Vulnerabilities in ZoneAlarm MailSafe
*****************************************************
Scope
-----------
Edvice recently tested ZoneLabs ZoneAlarm Pro ability to detect and
quarantine incoming e-mail attachments that may contain malicious code
or viruses. This functionality is provided by ZoneAlarm's MailSafe
feature.
The Findings
--------------------
We encountered several vulnerabilities in ZoneAlarm 3.0 MailSafe. The
vulnerabilities allow bypassing ZoneAlarm's e-mail protection.
Details
--------------
Most of the vulnerabilities we encountered are known Email Filters
attack techniques and there is no point in explaining them again.
However, there is one issue worth mentioning:
It is possible to bypass ZoneAlarm Email Protection by appending a dot
to the file name extension (e.g. malicious.exe becomes malicious.exe.).
The dot changes the file name extension and MailSafe fails to compare it
with known dangerous extensions. The MS-Windows operating system on the
other hand disregards a dot at the end of a file name. When Windows is
given a file name ending with a dot, it will automatically remove the
dot from the file name extension. When Outlook or Outlook Express
receives a file name that ends with a dot, it will present the dot, but
will launch the appropriate application when the file is double-clicked,
as if the dot does not exist.
Vendor Status
----------------------
ZoneLabs was first contacted on January 26, 2002.
A fix (v3.0.118) for most of the vulnerabilities we encountered,
including the one mentioned above, is available through ZoneAlarm's
Check for Update feature as from yesterday. ZoneLabs is still working on
one of the vulnerabilities and a fix is expected soon.
HTML Version: http://www.edvicesecurity.com/ad02-02.htm
----- End forwarded message -----
-- Bjarni R. Einarsson PGP: 02764305, B7A3AB89 38876@xyz.molar.is -><- http://bre.klaki.net/Check out my open-source email sanitizer: http://mailtools.anomy.net/ Spammers, please send plenty of email to: 39050@xyz.molar.is