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AUSCERT External Security Bulletin Redistribution
ESB-2002.077 -- Microsoft Security Bulletin MS02-005
11 February 2002 Cumulative Patch for Internet Explorer
18 February 2002
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AusCERT Security Bulletin Summary
---------------------------------
Product: Internet Explorer 5.01
Internet Explorer 5.5
Internet Explorer 6
Outlook 98
Outlook 2000
Outlook 2002
Outlook Express 6
Vendor: Microsoft
Operating System: Windows
Impact: Execute Arbitrary Code/Commands
Provide Misleading Information
Access Privileged Data
Access Required: Remote
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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.
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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:
===================
- A patch is available to fix this vulnerability. Please read the
Security Bulletin at
http://www.microsoft.com/technet/security/bulletin/ms02-005.asp
for information on obtaining this patch.
Acknowledgment:
===============
- The dH team and SECURITY.NNOV (http://www.security.nnov.ru/) team
for reporting the buffer overrun vulnerability.
- Sandro Gauci of GFI security labs (http://www.gfi.com) for
reporting the application invocation vulnerability.
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THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS
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