[NT] Cumulative Security Update For Internet Explorer (MS04-004)

From: SecuriTeam (support_at_securiteam.com)
Date: 02/04/04

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      Cumulative Security Update For Internet Explorer (MS04-004)
    ------------------------------------------------------------------------

    SUMMARY

    This is a cumulative update that includes the functionality of all the
    previously-released updates for Internet Explorer 5.01, Internet Explorer
    5.5, and Internet Explorer 6.0. Additionally, it eliminates the following
    three newly-discovered vulnerabilities:

     * A vulnerability that involves the cross-domain security model of
    Internet Explorer. The cross domain security model of Internet Explorer
    keeps windows of different domains from sharing information. This
    vulnerability could result in the execution of a script in the Local
    Machine zone. To exploit this vulnerability, an attacker would have to
    host a malicious Web site that contained a Web page designed to exploit
    the vulnerability and then persuade a user to view the Web page. The
    attacker could also create an HTML e-mail message designed to exploit the
    vulnerability and persuade the user to view the HTML e-mail message. After
    the user has visited the malicious Web site or viewed the malicious HTML
    e-mail message an attacker who exploited this vulnerability could access
    information from other Web sites, access files on a user's system, and run
    arbitrary code on a user's system. This code would run in the security
    context of the currently logged on user.

     * A vulnerability that involves performing a drag-and-drop operation with
    function pointers during dynamic HTML (DHTML) events in Internet Explorer.
    This vulnerability could allow a file to be saved in a target location on
    the user's system if the user clicked a link. No dialog box would request
    that the user approve this download. To exploit this vulnerability, an
    attacker would have to host a malicious Web site that contained a Web page
    that had a specially-crafted link. The attacker would then have to
    persuade a user to click that link. The attacker could also create an HTML
    e-mail message that had a specially-crafted link, and then persuade the
    user to view the HTML e-mail message and then click the malicious link. If
    the user clicked this link, code of the attacker's choice would not be
    executed, but could be saved on the user's computer in a targeted
    location.

     * A vulnerability that involves the incorrect parsing of URLs that
    contain special characters. When combined with a misuse of the basic
    authentication feature that has "username:password@" at the beginning of a
    URL, this vulnerability could result in a misrepresentation of the URL in
    the address bar of an Internet Explorer window. To exploit this
    vulnerability, an attacker would have to host a malicious Web site that
    contained a Web page that had a specially-crafted link. The attacker would
    then have to persuade a user to click that link. The attacker could also
    create an HTML e-mail message that had a specially-crafted link, and then
    persuade the user to view the HTML e-mail message and then click the
    malicious link. If the user clicked this link, an Internet Explorer window
    could open with a URL of the attacker's choice in the address bar, but
    with content from a Web Site of the attacker's choice inside the window.

    As with the previous Internet Explorer cumulative updates that were
    released with bulletins MS03-004, MS03-015, MS03-020, MS03-032, MS03-040,
    and MS03-048, this cumulative update causes the window.showHelp( ) control
    to no longer work if you have not applied the HTML Help update. If you
    have installed the updated HTML Help control from Microsoft Knowledge Base
    article <http://support.microsoft.com/default.aspx?scid=kb;en-us;811630>
    811630, you will still be able to use HTML Help functionality after you
    apply this update.

    This Internet Explorer cumulative update also includes a change to the
    functionality of a Basic Authentication feature in Internet Explorer. The
    update removes support for handling user names and passwords in HTTP and
    HTTP with Secure Sockets Layer (SSL) or HTTPS URLs in Microsoft Internet
    Explorer. The following URL syntax is no longer supported in Internet
    Explorer or Windows Explorer after you install this software update:

    http(s)://username:password@server/resource.ext

    For more information about this change, please see Microsoft Knowledge
    Base article <http://support.microsoft.com/default.aspx?scid=kb;en-us;>
    834489.

    Additionally, this update will disallow navigation to
    "username:password@host.com" URLs for XMLHTTP. Microsoft is currently
    creating an update to MSXML that will address this issue specifically for
    XMLHTTP and we will provide more information in this bulletin when the
    update becomes available.

    The update also refines a change made in Internet Explorer 6 Service Pack
    1, which prevents web pages in the Internet Security zone from navigating
    to the local computer zone. This is discussed further in the "Frequently
    Asked Questions" section of this bulletin.

    DETAILS

    Affected Components:
     * Internet Explorer 6 Service Pack 1:
    <http://www.microsoft.com/downloads/details.aspx?FamilyId=70530968-B59A-47C0-90D3-0C884910BC97&displaylang=en> Download the update
     * Internet Explorer 6 Service Pack 1 (64-Bit Edition):
    <http://www.microsoft.com/downloads/details.aspx?FamilyId=326EFFDA-8D86-4683-BC77-9BF410BC620D&displaylang=en> Download the update
     * Internet Explorer 6 for Windows Server 2003:
    <http://www.microsoft.com/downloads/details.aspx?FamilyId=D78AE4F7-8852-4A04-B8F6-1DE327E598F0&displaylang=en> Download the update
     * Internet Explorer 6 for Windows Server 2003 (64-Bit Edition):
    <http://www.microsoft.com/downloads/details.aspx?FamilyId=6A7894F0-789F-4152-9AE4-8DCB43404149&displaylang=en> Download the update
     * Internet Explorer 6:
    <http://www.microsoft.com/downloads/details.aspx?FamilyId=BE0C18BC-7F9A-4196-BFDE-29EBA8CF7A50&displaylang=en> Download the update
     * Internet Explorer 5.5 Service Pack 2:
    <http://www.microsoft.com/downloads/details.aspx?FamilyId=EFFE87F6-7ACA-4A54-B767-5597DDE95C6F&displaylang=en> Download the update
     * Internet Explorer 5.01 Service Pack 4:
    <http://www.microsoft.com/downloads/details.aspx?FamilyId=F5E74139-6E0E-49FD-9AA2-36D2D8454A92&displaylang=en> Download the update
     * Internet Explorer 5.01 Service Pack 3:
    <http://www.microsoft.com/downloads/details.aspx?FamilyId=202D3AAC-6B56-4F4A-8C0F-4183C77B6B51&displaylang=en> Download the update
     * Internet Explorer 5.01 Service Pack 2:
    <http://www.microsoft.com/downloads/details.aspx?FamilyId=17904608-DCEE-4C99-A780-81D6DBC48DD5&displaylang=en> Download the update

    Mitigating Factors:
    There are three common mitigating factors for both the Cross Domain
    Vulnerability and Drag-and-Drop Operation Vulnerability:

     * By default, Internet Explorer on Windows Server 2003 runs in Enhanced
    Security Configuration. This default configuration of Internet Explorer
    blocks automatic exploitation of this attack. If Internet Explorer
    Enhanced Security Configuration has been disabled, the protections that
    are put in place that prevent these vulnerabilities from being
    automatically exploited would be removed.

     * In the Web-based attack scenario, the attacker would have to host a Web
    site that contains a Web page that is used to exploit these
    vulnerabilities. An attacker would have no way to force a user to visit a
    malicious Web site. Instead, the attacker would have to lure them there,
    typically by getting them to click a link that takes them to the
    attacker's site.

     * By default, Outlook Express 6.0, Outlook 2002 and Outlook 2003 open
    HTML e-mail messages in the Restricted sites zone. Additionally, Outlook
    98 and 2000 open HTML e-mail messages in the Restricted sites zone if the
    Outlook E-mail Security Update has been installed. The risk of attack from
    the HTML email vector can be significantly reduced if the following
    conditions are met:
       * You have applied the update included with Microsoft Security bulletin
    MS03-040 or MS03-048
       * You are using Internet Explorer 6 or later
       * You are using the Microsoft Outlook Email Security Update or
    Microsoft Outlook Express 6.0 and higher, or Microsoft Outlook 2000 or
    later in its default configuration

     * If an attacker exploited these vulnerabilities, they would gain only
    the same privileges as the user. Users whose accounts are configured to
    have few privileges on the system would be at less risk than users who
    operate with administrative privileges.

    Vulnerability identifier
     * Travel Log Cross Domain Vulnerability
    <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-1026>
    CAN-2003-1026
     * Function Pointer Drag and Drop Vulnerability
    <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-1027>
    CAN-2003-1027
     * Improper URL Canonicalization Vulnerability
    <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-1025>
    CAN-2003-1025

    Workarounds
    Microsoft has tested the following workarounds that apply across both the
    Travel Log Cross Domain Vulnerability CAN-2003-1026 and the Drag and Drop
    Operation Vulnerability CAN-2003-1027 the vulnerabilities. These
    workarounds do not mitigate the Improper URL Canonicalization
    Vulnerability CAN-2003-1025. These workarounds help block known attack
    vectors. However they will not correct the underlying vulnerabilities.
    Workarounds may reduce functionality in some cases; in such cases, the
    reduction in functionality is identified below.

    Prompt before running ActiveX controls and active scripting in the
    Internet zone and in the Local Intranet zone
    You can help protect against these vulnerabilities by changing your
    settings for the Internet security zone to prompt before running ActiveX
    controls. To do this, follow these steps:

     * In Internet Explorer, click Internet Options on the Tools menu
     * Click the Security tab
     * Click Internet, and then click Custom Level
     * Under Settings, in the ActiveX controls and plug-ins section, under Run
    ActiveX controls and plug-ins, click Prompt
     * In the Scripting section, under Active Scripting, click Prompt, and
    then click OK
     * Click Local intranet, and then click Custom Level
     * Under Settings, in the ActiveX controls and plug-ins section, under Run
    ActiveX controls and plug-ins, click Prompt
     * In the Scripting section, under Active Scripting, click Prompt
     * Click OK two times to return to Internet Explorer

    Impact of Workaround
    There are side effects to prompting before running ActiveX controls. Many
    Web sites that are on the Internet or on an intranet use ActiveX to
    provide additional functionality. For example, an online e-commerce site
    or banking site may use ActiveX controls to provide menus, ordering forms,
    or even account statements. Prompting before running ActiveX controls is a
    global setting that affects all Internet and intranet sites. You will be
    prompted frequently when you enable this workaround. For each prompt, if
    you feel you trust the site that you are visiting, click Yes to run
    ActiveX controls. If you do not want to be prompted for all these sites,
    use the "Restrict Web sites to only your trusted Web sites" workaround.

    Restrict Web sites to only your trusted Web sites
    After you set Internet Explorer to require a prompt before it runs ActiveX
    in the Internet zone and in the Local Intranet zone, you can add sites
    that you trust to Internet Explorer's Trusted sites zone. This will allow
    you to continue to use trusted Web sites exactly as you do today, while
    helping to protect you from this attack on untrusted sites. Microsoft
    recommends that you only add sites that you trust to the Trusted sites
    zone.

     * In Internet Explorer, click Tools, click Internet Options, and then
    click the Security tab
     * In the Select a Web content zone to specify its current security
    settings box, click Trusted Sites, and then click Sites
     * If you want to add sites that do not require an encrypted channel,
    click to clear the Require server verification (https:) for all sites in
    this zone check box
     * In the Add this Web site to the zone box, type the URL of a site that
    you trust, and then click Add
     * Repeat these steps for each site that you want to add to the zone
     * Click OK two times to accept the changes and return to Internet
    Explorer

    Add any sites that you trust not to take malicious action on your
    computer. One in particular that you may want to add is
    "*.windowsupdate.microsoft.com" (without the quotes). This is the site
    that will host the update, and it requires the use of an ActiveX control
    to install the update.

    Impact of Workaround
    For those sites that you have not configured to be in your Trusted sites
    zone, their functionality will be impaired if they require the use of
    ActiveX controls to function correctly. Adding sites to your Trusted sites
    zone will allow them to be able to download the ActiveX control that they
    require to function correctly. However you should only add Web sites you
    trust to the Trusted sites zone.

    Install Outlook Email Security Update if you are using Outlook 2000 SP1 or
    earlier
    By default, the Outlook E-mail Security Update causes Outlook 98 and 2000
    to open HTML e-mail messages in the Restricted sites zone. By default,
    Outlook Express 6.0, Outlook 2002, and Outlook 2003 open HTML e-mail
    messages in the Restricted sites zone. Customers who use any of these
    products are at reduced risk from an e-mail-borne attack that tries to
    exploit this vulnerability, unless the user clicks a malicious link in the
    e-mail message.

    If you are using Outlook 2002 or Outlook Express 6.0 SP1 or later, read
    e-mail messages in plain text format to help protect yourself from the
    HTML e-mail attack vector.
    Microsoft Outlook 2002 users who have applied Service Pack 1 or later and
    Outlook Express 6.0 users who have applied Service Pack 1 or later can
    enable a feature that will enable them to view all non-digitally-signed
    e-mail messages or non-encrypted e-mail messages in plain text only.

    Digitally-signed e-mail messages and encrypted e-mail messages are not
    affected by the setting and may be read in their original formats.
    Information about how to enable this setting in Outlook 2002 can be found
    in the following Knowledge Base article:

     <http://support.microsoft.com/default.aspx?scid=kb;en-us;307594>
    http://support.microsoft.com/default.aspx?scid=kb;en-us;307594

    Information about how to enable this setting in Outlook Express 6.0 can be
    found in the following Knowledge Base article:

     <http://support.microsoft.com/?kbid=291387>
    http://support.microsoft.com/?kbid=291387

    Impact of Workaround
    E-mail that is viewed in plain text format cannot contain pictures,
    specialized fonts, animations, or other rich content. Additionally:

     * The changes are applied to the preview pane and to open messages
     * Pictures become attachments to avoid loss of message content
     * ecause the message is still in Rich Text Format or in HTML format in
    the store, the object model (custom code solutions) may behave
    unexpectedly because the message is still in Rich Text Format or in HTML
    format in the mail store

    Workarounds and other mitigations for the Improper URL Canonicalization
    Vulnerability
    <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-1025>
    CAN-2003-1025 can be found in Knowledge Base article
    <http://support.microsoft.com/default.aspx?scid=kb;%5bLN%5d;833786>
    833786.

    Frequently Asked Questions

    Why is the update available for Windows 98, Windows 98 Second Edition, and
    Windows Millennium Edition (Windows Me)?
    Security updates for these platforms would normally be available by
    request through assisted support channels, however since the issues
    repaired in this bulletin were reported publicly prior to this
    announcement the Internet Explorer 6 Service Pack 1 version of this patch
    will be supported on those operating systems for this release.

    What vulnerabilities are eliminated by this update?
    This is a cumulative update that incorporates the functionality of all
    previously released updates for Internet Explorer. Additionally, this
    update eliminates the following newly reported vulnerabilities:

     * A vulnerability that could allow an attacker to cause arbitrary code to
    run on the user's system
     * A vulnerability that could allow an attacker to save arbitrary code on
    the user's system
     * A vulnerability that could allow an attacker to mis-represent the
    location of a Web page in the Address bar of an Internet Explorer window

    What systems are primarily at risk from the vulnerability?
    Any system that has Internet Explorer installed is at risk from this
    vulnerability, and Microsoft recommends that this update should be
    installed immediately on all systems. However, this vulnerabilities
    require a user to be logged on and to be using Internet Explorer for any
    malicious action to occur. Therefore, any systems where Internet Explorer
    is actively used (such as user's workstations) are at the most risk from
    these vulnerabilities. Systems where Internet Explorer is not actively
    used (such as most server systems) are at a reduced risk.

    Does this Security Update contain any other changes to functionality in
    Internet Explorer?
    Yes. This Internet Explorer cumulative update also includes a change to
    the functionality of a Basic Authentication feature in Internet Explorer.
    The update removes support for handling user names and passwords in HTTP
    and HTTP with Secure Sockets Layer (SSL) or HTTPS URLs in Microsoft
    Internet Explorer. The following URL syntax is no longer supported in
    Internet Explorer or Windows Explorer after you install this software
    update:

    http(s)://username:password@server/resource.ext

    For more information about this change, please see the Frequently Asked
    Questions section for this specific issue in this bulletin or Microsoft
    Knowledge Base article
    <http://support.microsoft.com/default.aspx?scid=kb;en-us;834489> 834489.

    Additionally, this update will disallow navigation to
    "username:password@host.com" URLs for XMLHTTP. Microsoft is currently
    creating an update to MSXML that will address this issue specifically for
    XMLHTTP and we will provide more information in this bulletin when the
    update becomes available.

    Does the update contain any other security changes?
    he update also refines a change made in Internet Explorer 6 Service Pack
    1, which prevents web pages in the Internet zone from navigating to the
    Local Machine zone. This change was introduced to mitigate the effects of
    potential new cross domain vulnerabilities. The changes introduced in this
    update are further enhancements of the Internet Explorer 6 Service Pack 1
    restrictions.

    I am running Internet Explorer on Windows Server 2003. Does this mitigate
    some of these vulnerabilities?
    Yes. By default, Internet Explorer on Windows Server 2003 runs in a
    restricted mode that is known as Enhanced Security Configuration that
    mitigates both the Travel Log Cross Domain CAN-2003-1026 and the Drag and
    Drop Operation CAN-2003-1027 vulnerabilities. The Enhanced Security
    Configuration on Windows Server 2003 does not mitigate the Improper URL
    Canonicalization Vulnerability CAN-2003-1025.

    What is Internet Explorer Enhanced Security Configuration?
    Internet Explorer Enhanced Security Configuration is a group of
    preconfigured Internet Explorer settings that reduce the likelihood of a
    user or of an administrator downloading and running malicious Web content
    on a server. Internet Explorer Enhanced Security Configuration reduces
    this risk by modifying numerous security-related settings, including the
    settings on the Security and the Advanced tab in the Internet Options
    dialog box. Some of the important modifications include:

     * Security level for the Internet zone is set to High. This setting
    disables scripts, ActiveX controls, Microsoft Java Virtual Machine
    (MSJVM), HTML content, and file downloads
     * Automatic detection of intranet sites is disabled. This setting assigns
    all intranet Web sites and all Universal Naming Convention (UNC) paths
    that are not explicitly listed in the Local intranet zone to the Internet
    zone
     * Install On Demand and non-Microsoft browser extensions are disabled.
    This setting prevents Web pages from automatically installing components
    and prevents non-Microsoft extensions from running
     * Multimedia content is disabled. This setting prevents music,
    animations, and video clips from running

    Disabling Internet Explorer Enhanced Security Configuration would remove
    the protections that are put in place to help prevent this vulnerability
    from being exploited.

    Is there any configuration of Windows Server 2003 that is likely to have
    Internet Explorer Enhanced Security Configuration disabled?
    Yes. Systems Administrators who have deployed Windows Server 2003 as a
    Terminal Server would likely disable Internet Explorer Enhanced Security
    Configuration to allow users of the Terminal Server to use Internet
    Explorer in an unrestricted mode.

    CAN-2003-1026: Travel Log Cross Domain Vulnerability Could Allow Remote
    Code Execution
    What is the scope of this vulnerability?
    This vulnerability could allow a malicious Web site operator to access
    information in another Internet or intranet domain or on the user's local
    system by injecting specially-crafted code when the browser parses
    specially formatted Script URLs from the travel log. This could also allow
    an attacker to run an executable file of their choice on the user's
    system.

    What causes the vulnerability?
    The process used to validate Script URLs in Internet Explorer's Travel Log
    causes this vulnerability.

    What is Internet Explorer's travel log?
    Internet Explorer's travel log is an interface that maintains a navigation
    stack for the WebBrowser control. This stack is used by Internet Explorer
    to maintain a list of recently visited sites. For example, the History tab
    in Internet Explorer is built based on information from the travel log.

    What is the cross-domain security model that Internet Explorer implements?
    One of the principal security functions of a browser is to make sure that
    browser windows that are under the control of different Web sites cannot
    interfere with each other or access each other's data, while allowing
    windows from the same site to interact with each other. To differentiate
    between cooperative and uncooperative browser windows, the concept of a
    "domain" has been created. A domain is a security boundary - any open
    windows within the same domain can interact with each other, but windows
    from different domains cannot. The cross-domain security model is the part
    of the security architecture that keeps windows from different domains
    from interfering with each other.

    The simplest example of a domain is associated with Web sites. If you
    visit http://www.microsoft.com, and it opens a window to
    http://www.microsoft.com/security, the two windows can interact with each
    other because both sites belong to the same domain,
    http://www.microsoft.com. However, if you visited
    http://www.microsoft.com, and it opened a window to a different Web site,
    the cross-domain security model would protect the two windows from each
    other. The concept goes even further. The file system on your local
    computer is also a domain. For example, http://www.microsoft.com could
    open a window and show you a file on your hard disk. However, because your
    local file system is in a different domain from the Web site, the
    cross-domain security model should prevent the Web site from reading the
    file that is being displayed.

    The Internet Explorer cross-domain security model can be configured by
    using the security zone settings in Internet Explorer.

    What are Internet Explorer security zones?
    Internet Explorer security zones are a system that divides online content
    into categories or zones based on its trustworthiness. Specific Web
    domains can be assigned to a zone, depending on how much trust is placed
    in the content of each domain. The zone then restricts the capabilities of
    the Web content, based on the zone's policy. By default, most Internet
    domains are treated as part of the Internet zone, which has default policy
    that prevents scripts and other active code from accessing resources on
    the local system.

    What is the issue with the way Internet Explorer calculates cross domain
    security?
    Internet Explorer evaluates security when one Web Page requests access to
    resources in another security zone. However, there is a vulnerability in
    the process used to calculate security when specially formatted Script
    URLs are parsed out of the Travel Log. As a result, an attacker can bypass
    the security checks.

    What could this vulnerability enable an attacker to do?
    An attacker could use this vulnerability to create a Web page that could
    allow the attacker to access data across domains. This could include
    accessing information from other Web sites, from local files on the
    system, or from running executable files that already exist on the local
    file system. This could also include running executable files of the
    attacker's choice on the user's local file system.

    How could an attacker exploit this vulnerability?
    An attacker could exploit this vulnerability by creating a malicious Web
    page or an HTML e-mail message and then enticing the user to visit this
    page or to view the HTML e-mail message. When the user visited the page or
    viewed the e-mail message, the attacker could access information from
    other websites, local files on the system, or cause script to run in the
    security context of the Local Machine Zone.

    What does the update do?
    The update addresses the vulnerability by ensuring that cross domain
    security checks take place whenever Script URLs are parsed from the Travel
    Log.

    CAN-2003-1027: Function Pointer Drag and Drop Operation Vulnerability
    Could Allow Arbitrary Code to be Saved on User's System
    What is the scope of the vulnerability?
    This vulnerability involves using a drag and drop event in Internet
    Explorer with function pointers and could result in a file being saved on
    the user's system when the user clicked a link (the user would not receive
    a dialog box requesting to approve the download). To exploit this
    vulnerability, an attacker would have to host a malicious Web site or
    create an HTML e-mail that contained a link that is designed to exploit
    this particular vulnerability and then persuade a user to visit that site.
    If the user visited the page or viewed the e-mail message, and if the user
    clicked the malicious link, then code of the attacker's choice could be
    saved in a targeted location on the user's computer.

    What causes the vulnerability?
    The process by which the drag and drop technology validates certain
    Dynamic HTML (DHTML) events causes this vulnerability. As a result, a file
    could be downloaded to the user's system after the user clicks a link.

    What are DHTML events?
    DHTML events are special actions that are provided by the DHTML Object
    Model. These events can be used in script code to add dynamic content to a
    Web site.

    What might an attacker use the vulnerability to do?
    An attacker who successfully exploited this vulnerability could save code
    of their choice to the user's local file system. Although this code could
    not be executed through this vulnerability directly, the operating system
    might open the file if it is dropped to a sensitive location, or a user
    may click the file inadvertently, causing the attacker's code to be
    executed.

    How could an attacker exploit this vulnerability?
    To exploit this vulnerability, an attacker would have to host a malicious
    Web site that contained a Web page or an HTML e-mail with a link that is
    designed to exploit this particular vulnerability and then persuade a user
    to visit that site. If the user clicked the malicious link, any code of
    the attacker's choice could be saved on the user's computer in a targeted
    location.

    What systems are primarily at risk from the vulnerability?
    Any system that has Internet Explorer installed is at risk from this
    vulnerability, and this update should be installed immediately on all
    systems. However, this vulnerability requires a user to be logged on and
    to be using Internet Explorer for any malicious action to occur.
    Therefore, any systems where Internet Explorer is actively used (such as
    user's workstations) are at the most risk from this vulnerability. Systems
    where Internet Explorer is not actively used (such as most server systems)
    are a reduced risk.

    What does the update do?
    This update corrects this vulnerability by correctly evaluating
    drag-and-drop operations by using function pointers during DHTML events.

    CAN-2003-1025: Improper URL Canonicalization Vulnerability Could Allow
    Attacker to Spoof Websites
    What's the scope of the vulnerability?
    There is a vulnerability that involves the address bar that is used by
    Internet Explorer to display the currently visited Web site. This
    vulnerability could result in an incorrect URL being listed in the Address
    bar that is not the actual Web page that is displayed by Internet
    Explorer.

    What causes the vulnerability?
    This vulnerability is caused by a canonicalization error that occurs when
    Internet Explorer parses special characters in a HTTP URL.

    What is an HTTP URL?
    An HTTP URL is a Uniform Resource Locator used to designate an address to
    a resource reachable via the HTTP protocol. While the generic syntax for a
    URIs is defined in <http://www.ietf.org/rfc/rfc2396.txt> RFC 2396 -
    Uniform Resource Identifiers (URI): Generic Syntax, the specific syntax
    for a HTTP URL is defined in
    <http://www.w3.org/Protocols/rfc2616/rfc2616.html> RFC 2616 - Hypertext
    Transfer Protocol -- HTTP/1.1:

    http_URL = "http:" "//" host [ ":" port ] [ abs_path [ "?" query ]]

    What might an attacker use the vulnerability to do?
    An attacker could use this vulnerability to create a Web Page that would
    display a URL of the attackers choosing in the address bar, while
    displaying a different Web Site in the browser window. An attacker could
    use this vulnerability to create a malicious page that spoofs a legitimate
    site. For example an attacker could create a Web Page that looks like a
    user's on-line E-mail site. While this Web Page would be hosted on a
    malicious Web Site, an attacker could use this vulnerability to display a
    legitimate looking URL in the address bar. A user might see this URL and
    mistakenly give away sensitive information to the attacker's site.

    How could an attacker exploit this vulnerability?
    To exploit one of this vulnerability, an attacker would have to host a
    malicious Web site that contains a Web page that has a specially-crafted
    link. The attacker would then have to persuade a user to click that link.
    The attacker could also create an HTML e-mail message that has a
    specially-crafted link, and then persuade the user to view the HTML e-mail
    message and then click the malicious link. If the user clicked this link,
    an Internet Explorer window could open with an HTTP URL of the attacker's
    choice in the Address bar, but with content from a Web site of the
    attacker's choice.

    What does the update do?
    The update corrects the vulnerability by making sure that Internet
    Explorer correctly parses special characters in URLs to make sure that the
    correct address is represented in the Address bar. This update also makes
    Internet Explorer's handling of HTTP URLs more compliant with RFC 2616
    Hypertext Transfer Protocol -- HTTP/1.1 by removing the ability to perform
    basic authentication by using a "username:password@" format. This change
    to the default behavior of Internet Explorer is discussed further in
    Knowledge Base article
    <http://www.support.microsoft.com/default.aspx?scid=kb;%5bLN%5d;834489>
    834489.

    ADDITIONAL INFORMATION

    The information has been provided by Microsoft Product Security
    The original article can be found at:
    <http://www.microsoft.com/technet/security/bulletin/winfeb04.asp>
    http://www.microsoft.com/technet/security/bulletin/winfeb04.asp

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