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HistoryFeb 15, 2002 - 12:00 a.m.

Microsoft Security Bulletin MS02-005

2002-02-1500:00:00
vulners.com
33

Title: 11 February 2002 Cumulative Patch for Internet Explorer
Date: 11 February 2002
Software: Internet Explorer
Impact: Run Code of Attacker's Choice
Max Risk: Critical
Bulletin: MS02-005

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS02-005.asp.


Issue:

This is a cumulative patch that, when installed, eliminates all
previously discussed security vulnerabilities affecting IE 5.01, 5.5
and IE 6. In addition, it eliminates the following six newly
discovered vulnerabilities:

  • A buffer overrun vulnerability associated with an HTML directive
    that's used to incorporate a document within a web page. By
    creating a web page that invokes the directive using specially
    selected attributes, an attacker could cause code to run on the
    user's system.

  • A vulnerability associated with the GetObject scripting function.
    Before providing a handle to an operating system object,
    GetObject performs a series of security checks to ensure that the
    caller has sufficient privileges to it. However, by requesting a
    handle to a file using a specially malformed representation, it
    would be possible to bypass some of these checks, thereby
    allowing a web page to complete an operation that should be
    prevented, namely, reading files on the computer of a visiting
    user's system.

  • A vulnerability related to the display of file names in the File
    Download dialogue box. When a file download from a web site is
    initiated, a dialogue provides the name of the file and lets the
    user choose what action to take. However, a flaw exists in the way
    HTML header fields (specifically, the Content-Disposition and
    Content-Type fields) are handled. This flaw could make it possible
    for an attacker to misrepresent the name of the file in the
    dialogue, in an attempt to trick a user into opening or saving
    an unsafe file.

  • A vulnerability that could allow a web page to open a file on the
    web site, using any application installed on a user's system.
    By design, IE should only open a file on a web site using the
    application that's registered to that type of file, and even
    then only if it's on a list of safe applications. However,
    through a flaw in the handling of the Content-Type HTML
    header field, an attacker could circumvent this restriction,
    and specify the application that should be invoked to process
    a particular file. IE would comply, even if the application was
    listed as unsafe.

  • A vulnerability that could enable a web page to run a script even
    if the user has disabled scripting. IE checks for the presence of
    scripts when initially rendering a page. However, the capability
    exists for objects on a page to respond to asynchronous events;
    by misusing this capability in a particular way, it could be
    possible for a web page to fire a script after the page has
    passed the initial security checks.

  • A newly discovered variant of the "Frame Domain Verification"
    vulnerability discussed in Microsoft Security Bulletin MS01-058.
    The vulnerability could enable a malicious web site operator to
    open two browser windows, one in the web site's domain and the
    other on the user's local file system, and to use the
    Document.open function to pass information from the latter to
    the former. This could enable the web site operator to read, but
    not change, any file on the user's local computer that could be
    opened in a browser window. In addition, this could be used to
    mis-represent the URL in the address bar in a window opened from
    their site.

Mitigating Factors:

Buffer Overrun in HTML Directive:

  • The vulnerability could not be exploited if the "Run ActiveX
    Controls and Plugins" security option were disabled in the
    Security Zone in which the page was rendered. This is the default
    condition in the Restricted Sites Zone, and can be disabled
    manually in any other Zone.

  • Outlook 98 and 2000 (after installing the Outlook Email Security
    Update), Outlook 2002, and Outlook Express 6 all open HTML mail
    in the Restricted Sites Zone. As a result, customers using these
    products would not be at risk from email-borne attacks.

  • The buffer overrun would allow code to run in the security context
    of the user rather than the system. The specific privileges the
    attacker could gain through this vulnerability would therefore
    depend on the privileges accorded to the user.

File Reading via GetObject function:

  • This vulnerability could only be used to read files. It could not
    be used to create, change, delete, or execute them.

  • The attacker would need to know the name and location of the file
    on the user's computer.

  • Some files that would be of interest to an attacker - most
    notably,the SAM Database - are locked by the operating system
    and therefore could not be read even using this vulnerability.

  • The email-borne attack scenario would be blocked if the user were
    using any of the following: Outlook 98 or 2000 with the Outlook
    Email Security Update installed; Outlook 2002; or Outlook
    Express 6.

  • The web-based attack scenario could be blocked by judicious use of
    the IE Security Zones mechanism such as using the Restricted Sites
    zone.

File Download Dialogue Spoofing via Content-Type and
Content-Disposition fields:

  • Exploiting this vulnerability would not give an attacker the
    ability to force code to run on a user's system. It would only
    enable the attacker to misrepresent the file name and type in the
    File Download dialogue. The download operation would not occur
    without the user's approval, and the user could cancel at any
    time.

  • The vulnerability could not be exploited if File Downloads have
    been disabled in the Security Zone in which the e-mail is
    rendered. This is not a default setting in any zone, however.

  • On versions of IE prior to 6.0, the default selection in the file
    download dialogue is to save, rather than open, the file. (In
    IE 6.0, the default is to open the file; however, this behavior
    is inappropriate, and the patch changes IE 6.0 to conform with the
    behavior of previous versions).

Application invocation via Content-Type field:

  • An attacker could only exploit this vulnerability if the
    application specified through the Content-Type field was actually
    installed on the user's system.

  • The vulnerability does not provide any way for the attacker to
    inventory the applications installed on the user's system and
    select one, nor does it provide any way to force the user to
    install a particular application.

  • The vulnerability would not provide any way to circumvent the
    security features of the application or to reconfigure it.

  • Outlook 2002 users who have configured Outlook to render HTML mail
    as plaintext would be at no risk from attack through HTML mail.

Script execution:

  • This vulnerability extends only to allowing scripts to run - it
    does not allow any other security restrictions to be bypassed.
    So, for instance, although an attacker could use this
    vulnerability to run a script, the script would still be subject
    to all other expected security settings.

Frame Domain Verification Variant via Document.Open function:

  • The vulnerability could only be used to view files. It could
    not be used to create, delete, modify or execute them.

  • The vulnerability would only allow an attacker to read files that
    can be opened in a browser window, such as image files, HTML files
    and text files. Other file types, such as binary files, executable
    files, Word documents, and so forth, could not be read.

  • The attacker would need to specify the exact name and location of
    the file in order to read it.

Risk Rating:

  • Internet systems: Critical
  • Intranet systems: Critical
  • Client systems: Critical

Patch Availability:

Acknowledgment:


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