Alert: Microsoft Security Bulletin - MS02-066

From: Russ (Russ.Cooper@RC.ON.CA)
Date: 11/21/02

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    Date:         Wed, 20 Nov 2002 18:50:55 -0500
    From: Russ <Russ.Cooper@RC.ON.CA>

    Cumulative Patch for Internet Explorer (Q328970)

    Originally posted: November 20, 2002


    Who should read this bulletin: Customers using Microsoft® Internet Explorer

    Impact of vulnerability: Six new vulnerabilities, the most serious of which could enable an attacker to execute commands on a user's system.

    Maximum Severity Rating: Important

    Recommendation: Customers should install the patch at the earliest opportunity.

    Affected Software:
    - Microsoft Internet Explorer 5.01
    - Microsoft Internet Explorer 5.5
    - Microsoft Internet Explorer 6.0

    End User Bulletin: An end user version of this bulletin is available at:

    Technical description:

    This is a cumulative patch that includes the functionality of all previously released patches for IE 5.01, 5.5 and 6.0. In addition, it eliminates the following six newly discovered vulnerabilities:
    - A buffer overrun vulnerability that occurs because Internet Explorer does not correctly check the parameters of a PNG graphics file when it is opened. To the best of Microsoft's knowledge, this vulnerability could only be used to cause Internet Explorer to fail. The effect of exploiting the vulnerability against Internet Explorer would be relatively minor - the user would only need to restart the browser to restore normal operation. However, a number of other Microsoft products - notably, most Microsoft Office products and Microsoft Index Server - rely on Internet Explorer to render PNG files, and exploiting the vulnerability against such an application would cause them to fail as well. Because of this, Microsoft recommends that customers install this patch regardless of whether they are using Internet Explorer as their primary web browser.
    - An information disclosure vulnerability related to the way that Internet Explorer handles encoded characters in a URL. This vulnerability could allow an attacker to craft a URL containing some encoded characters that would redirect a user to a second web site. If a user followed the URL, the attacker would be able to piggy-back the user's access to the second website. This could allow the attacker to access any information the user shared with the second web site.
    - A vulnerability that occurs because under certain circumstances Internet Explorer does not correctly check the component that the OBJECT tag calls. This could allow an attacker to obtain the name of the Temporary Internet Files folder on the user's local machine. The vulnerability would not allow an attacker to read or modify any files on the user's local system, since the Temporary Internet Files folder resides in the Internet security zone. Knowledge of the name of the Temporary Internet Files folder could allow an attacker to identify the username of the logged-on user and read other information in the Temporary Internet Files folder such as cookies.
    - Three vulnerabilities that although having differing root causes, have the same net effects. All three vulnerabilities result because of incomplete security checks being carried out when using particular programming techniques in web pages, and would have the effect of allowing one website to access information in another domain, including the user's local system. This could enable the web site operator to read, but not change, any file on the user's local computer that could be viewed in a browser window. In addition, this could also enable an attacker to invoke an executable that was already present on the local system.

    In addition, the patch sets the Kill Bit on a legacy DirectX ActiveX control which has been retired but which has a security vulnerability. This has been done to ensure that the vulnerable control cannot be reintroduced onto users' systems and ensures that users who already have the control on their system are protected. This is discussed further in Microsoft Knowledge Base Article 810202.

    The patch also makes a further refinement to cross domain verification check that was first introduced in Internet Explorer Service Pack 1. This is discussed further in the Frequently Asked Questions below.

    Mitigating factors:
    With the exception of the Malformed PNG Image File Failure, there are common mitigating factors across all of the vulnerabilities:
    - The attacker would have to host a web site that contained a web page used to exploit the particular vulnerability.
    - 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 mails in the Restricted Sites Zone. In addition, Outlook 98 and 2000 open HTML mails 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 these vulnerabilities. In addition to there are a number of individual mitigating factors:

    Malformed PNG Image File Failure
    - Internet Explorer and other affected applications such as Microsoft Office and Microsoft Index Server could be successfully restarted after the failure.
    - Microsoft has not identified a method by which this buffer overrun can be used to execute code of the attacker's choice on the user's system.
    - This vulnerability is not present in Internet Explorer 6 Service Pack 1.Encoded Characters Information Disclosure
    - The vulnerability would not enable an attacker to read, modify or execute any files on the local system.Temporary Internet Files folder Name Reading
    - An attacker could not use this vulnerability to read, delete or modify any files on the user's local system other than information contained in the Temporary Internet Files folder.
    - An attacker could only exploit this vulnerability by having a user visit a malicious web site and then follow a malformed link on this malicious web site to a second web site that the user trusted.
    - This vulnerability is not present in Internet Explorer 6 Service Pack 1.Frames Cross Site Scripting, Cross Domain Verification via Cached Methods & Improper Cross Domain Security Validation with Frames
    - The vulnerabilities would only allow an attacker to read files on the user's local system that can be rendered in a browser window, such as image files, HTML files and text files.
    - The vulnerabilities would not provide any way for an attacker to put a program of their choice onto another user's system.
    - An attacker would need to know the name and location of any file on the system to successfully invoke it.
    - The vulnerabilities could only be used to view or invoke local executables. It could not be used to create, delete, or modify arbitrary or malicious files.

    Vulnerability identifiers:
    - Malformed PNG Image File Failure: CVE-CAN-2002-1185
    - Encoded Characters Information Disclosure: CVE-CAN-2002-1186
    - Frames Cross Site Scripting: CVE-CAN-2002-1187
    - Temporary Internet Files folder Name Reading: CVE-CAN-2002-1188
    - Cross Domain Verification via Cached Methods: CVE-CAN-2002-1254
    - Improper Cross Domain Security Validation with Frames: CVE-CAN-2002-1217

    This email is sent to NTBugtraq automatically as a service to my subscribers. Since its programmatically created, and since its been a long time since anyone paid actual money for my programming skills, it may or may not look that good...;-]

    I can only hope that the information it does contain can be read well enough to serve its purpose.

    Russ - Surgeon General of TruSecure Corporation/NTBugtraq Editor

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