IceWarp WebMail Server: Cross Site Scripting in Email View
During a penetration test, RedTeam Pentesting discovered that the IceWarp
WebMail Server is prone to Cross Site Scripting attacks in its email view.
for example, to steal users' session IDs.
Product: IceWarp eMail Server / WebMail Server
Affected Versions: 9.4.1
Fixed Versions: 9.4.2
Vulnerability Type: Cross Site Scripting
Security Risk: high
Vendor URL: http://www.icewarp.com/
Vendor Status: notified, fixed version released
Advisory URL: http://www.redteam-pentesting.de/advisories/rt-sa-2009-001
Advisory Status: published
CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-1467
"Feature complete yet easy to use, WebMail Server Pro provides feature
rich Web 2.0 web-based access to email, calendars, contacts, files and
shared data from any computer with browser and internet connection,
without the usual configuration hassle. Thanks to advanced technologies
and application-like look and feel, Pro suggests it was born to become the
ultimate replacement of Outlook and similar desktop mail clients."
(from the vendor's homepage)
and to remove unwanted HTML tags, the IceWarp WebMail Server filters HTML
emails with the function cleanHTML() that is defined in the PHP file
This filtering function can be circumvented in various ways, to still
allow XSS to happen.
Beginning in line 462 down to line 482, the cleanHTML() function removes
or changes a variety of keywords which are considered malicious. This
includes the removal of all attributes starting with "on" (e.g.
"vbscript" to "noscript".
Later, in line 485, the cleanHTML() function completely removes various HTML
tags from the email:
$string = preg_replace('#</*(meta|xml|blink|link|embed|object|iframe|
By inserting one of these HTML tags, which gets removed by the filtering
function, between the keywords which get filtered before, the cleanHTML()
function will not recognize them anymore. Later, it will remove the HTML
tag and thereby make the keyword valid again.
Proof of Concept Tag Removal
An HTML email with the following content will open an alert box in
victims' browsers when they move the mouse over the "XSS" text of the
support, during the penetration test Firefox 3.x was used.
Another way to circumvent the filtering is to use hex-encoded HTML
entities. The character "j" can e.g. be encoded as "j". The
cleanHTML() function decodes the given string once in line 459:
$string = html_entity_decode($string, ENT_COMPAT, "UTF-8");
By double encoding the input, all regular expressions used for filtering
will fail to recognize malicious content even after the first decoding.
The effect of this vulnerability is limited by the fact that HTML
encoded entities are recognized by browsers only if they are part of a
text node or attribute values.
Proof of Concept Hex Encoding
The "src" attribute value of the HTML tag
can be double encoded as
This will be decoded by the html_entity_decode() function in line 459 to
The value of the "src" attribute will not be recognized by the filtering
attempts following the decoding in the cleanHTML() function.
values in image elements' "src" attributes. This particular proof of
concept works with Internet Explorer 6, the newest Firefox will not
Users can disable the HTML message view in their configuration, so emails
are only displayed as plaintext.
Upgrade to version 9.4.2.
The risk of this vulnerability is estimated as high. Attackers have the
are thereby able to steal, for example, the users' session IDs. Users
itself to work properly.
2009-03-23 Vulnerabilities identified during a penetration test
2009-04-01 Meeting with customer and vendor
2009-04-28 CVE number assigned
2009-05-05 Vendor publishes fixed version
2009-05-05 Advisory released
RedTeam Pentesting GmbH
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