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National Cyber Alert System
Technical Cyber Security Alert TA06-262A
Microsoft Internet Explorer VML Buffer Overflow
Original release date: September 19, 2006
Last revised: September 26, 2006
Source: US-CERT
Systems Affected
* Microsoft Windows
* Microsoft Internet Explorer
Overview
Microsoft Internet Explorer (IE) fails to properly handle Vector
Markup Language (VML) tags. This creates a buffer overflow
vulnerability that could allow a remote attacker to execute arbitrary
code.
I. Description
Microsoft Internet Explorer contains a stack buffer overflow in code
that handles VML. More information is available in Vulnerability Note
VU#416092, Microsoft Security Advisory (925568), and Microsoft
Security Bulletin MS06-055.
Note that this vulnerability is being exploited.
II. Impact
By convincing a user to open a specially crafted HTML document, such
as a web page or HTML email message, a remote attacker could execute
arbitrary code with the privileges of the user running IE.
III. Solution
Apply update from Microsoft
Microsoft has provided an update to correct this vulnerability in
Microsoft Security Bulletin MS06-055.
This update is available on the Microsoft Update site.
System administrators may wish to consider using Windows Server Update
Services (WSUS).
Disable VML support
Microsoft Security Advisory (925568) suggests the following techniques
to disable VML support:
* Un-register Vgx.dll on Windows XP Service Pack 1; Windows XP
Service Pack 2; Windows Server 2003 and Windows Server 2003
Service Pack 1
* Modify the Access Control List on Vgx.dll to be more restrictive
* Configure Internet Explorer 6 for Microsoft Windows XP Service
Pack 2 to disable Binary and Script Behaviors in the Internet and
Local Intranet security zone
Disabling VML support may cause web sites and applications that use
VML to function improperly.
Render email as plain text
Microsoft Security Advisory (925568) suggests configuring Microsoft
Outlook and Outlook Express to render email messages in plain text
format.
Do not follow unsolicited links
In order to convince users to visit their sites, attackers often use
URL encoding, IP address variations, long URLs, intentional
misspellings, and other techniques to create misleading links. Do not
click on unsolicited links received in email, instant messages, web
forums, or internet relay chat (IRC) channels. Type URLs directly into
the browser to avoid these misleading links. While these are generally
good security practices, following these behaviors will not prevent
exploitation of this vulnerability in all cases, particularly if a
trusted site has been compromised or allows cross-site scripting.
IV. References
* Vulnerability Note VU#416092 -
<http://www.kb.cert.org/vuls/id/416092>
* Microsoft Security Bulletin MS06-055-
<http://www.microsoft.com/technet/security/bulletin/ms06-055.mspx>
* Microsoft Security Advisory (925568) -
<http://www.microsoft.com/technet/security/advisory/925568.mspx>
* Securing Your Web Browser-
<http://www.us-cert.gov/reading_room/securing_browser/#Internet_Explorer>
* Microsoft Update - <https://update.microsoft.com/microsoftupdate/>
* CVE-2006-3866 -
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-3866>
____________________________________________________________________
The most recent version of this document can be found at:
<http://www.us-cert.gov/cas/techalerts/TA06-262A.html>
____________________________________________________________________
Feedback can be directed to US-CERT Technical Staff. Please send
email to <cert@xxxxxxxx> with "TA06-262A Feedback VU#416092" in the
subject.
____________________________________________________________________
For instructions on subscribing to or unsubscribing from this
mailing list, visit <http://www.us-cert.gov/cas/signup.html>.
____________________________________________________________________
Produced 2006 by US-CERT, a government organization.
Terms of use:
<http://www.us-cert.gov/legal.html>
____________________________________________________________________
Revision History
September 19, 2006: Initial release
September 21, 2006: Fixed misspelling and removed IE-specific
language from Solution section
September 26, 2006: Added update information and added a reference
to Microsoft Update
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