Microsoft Security Bulletin MS03-004: Cumulative Patch for Internet Explorer (810847)

2003-02-07T00:00:00
ID SECURITYVULNS:DOC:4053
Type securityvulns
Reporter Securityvulns
Modified 2003-02-07T00:00:00

Description

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Title: Cumulative Patch for Internet Explorer (810847) Date: 05 February 2003 Software: Microsoft Internet Explorer Impact: Allow an attacker to execute commands on a user's system. Max Risk: Critical Bulletin: MS03-004

Microsoft encourages customers to review the Security Bulletins at: http://www.microsoft.com/technet/security/bulletin/ms03-004.asp http://www.microsoft.com/security/security_bulletins/ms03-004.asp


Issue:

This is a cumulative patch that includes the functionality of all previously released patches for IE 5.01, 5.5, 6.0. In addition, it eliminates two newly discovered vulnerabilities involving Internet Explorer's cross-domain security model - which keeps windows of different domains from sharing information. These flaws results in Internet Explorer because incomplete security checking causes Internet Explorer to allow one website to potentially access information from another domain when using certain dialog boxes.

In order to exploit this flaw, an attacker would have to host a malicious web site that contained a web page designed to exploit this particular vulnerability and then persuade a user to visit that site. Once the user has visited the malicious web site, it would be possible for the attacker to run malicious script by misusing a dialog box and cause that script to access information in a different domain. In the worst case, this could enable the web site operator to load malicious code onto a user's system. In addition, this flaw could also enable an attacker to invoke an executable that was already present on the local system.

A related cross-domain vulnerability allows Internet Explorer's showHelp() functionality to execute without proper security checking. showHelp() is one of the help methods used to display an HTML page containing help content. showHelp() allows more types of pluggable protocols than necessary, and this could potentially allow an attacker to access user information, invoke executables already present on a user's local system or load malicious code onto a user's local system.

The requirements to exploit this vulnerability are the same as for the issue described above: an attacker would have to host and lure a user to a malicious web site. In this scenario, the attacker could open a showHelp window to a known local file on the visiting user's local system and gain access to information from that file by sending a specially crafted URL to a second showHelp window. The attacker could also potentially access user information or run code of attacker's choice.

This cumulative patch will cause window.showHelp( ) to cease to function. When the latest HTML Help update - which is being released via Windows Update with this patch - is installed, window.showHelp( ) will function again, but with some limitations (see the caveats section later in this bulletin). This has been necessary in order to block the attack vector that might allow a web site operator to invoke an executable that was already present on a user's local system.

Mitigating Factors:

  • The attacker would have to host a web site that contained a web page used to exploit either of these cross-domain vulnerabilities.
  • The attacker would have no way to force users to visit the site. Instead, the attacker would need to lure them there, typically by getting them to click on a link that would take them to the attacker's site.
  • By default, Outlook Express 6.0 and Outlook 2002 open HTML mail in the Restricted Sites Zone. In addition, Outlook 98 and 2000 open HTML mail in the Restricted Sites Zone if the Outlook Email Security Update has been installed. Customers who use any of these products would be at no risk from an e-mail borne attack that attempted to exploit this vulnerability unless the user clicked a malicious link in the email.
  • Internet Explorer 5.01 users are not affected by the first vulnerability.

Risk Rating:

  • Internet Explorer 5.01: Critical
  • Internet Explorer 5.5: Critical
  • Internet Explorer 6.0: Critical

Patch Availability:

  • A patch is available to fix this vulnerability. Please read the Security Bulletins at

http://www.microsoft.com/technet/security/bulletin/ms03-004.asp http://www.microsoft.com/security/security_bulletins/ms03-004.asp

for information on obtaining this patch.

Acknowledgment:

  • Andreas Sandblad, Sweden for reporting the cross domain vulnerability using showhelp.

Home User Security Notification Service

Microsoft is now offering the Microsoft Security Update, a security bulletin notification service for home users. To learn more about this service, please go to:

http://www.microsoft.com/security/security_bulletins/decision.asp


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