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Title: Flaw in Microsoft VM Could Enable System
Date: 11 December 2002
Software: Microsoft VM
Impact: Eight vulnerabilities, the most serious of which
would enable an attacker to gain control over
another user's system.
Max Risk: Critical
Microsoft encourages customers to review the Security Bulletins at:
The Microsoft VM is a virtual machine for the Win32(r) operating
environment. The Microsoft
VM shipped in most versions of Windows (a complete list is available
in the FAQ), as well as
in most versions of Internet Explorer.
A new version of the Microsoft VM is available, which includes all
previously released fixes
for the VM, as well as fixes for eight newly reported security
issues. The attack vectors
for all of the new issues would likely be the same. An attacker would
create a web page
that, when opened, exploits the desired vulnerability, and either
host it on a web page or
send it to a user as an HTML mail.
The newly reported security issues are as follows:
- A security vulnerability through which an untrusted
Java applet could access COM objects. By design, COM
objects should only be available to trusted Java
programs because of the functionality they expose. COM
objects are available that provide functionality through
which an attacker could take control of the system.
- A pair of vulnerabilities that, although having
different underlying causes, would have the same effect,
namely, disguising the actual location of the applet's
codebase. By design, a Java applet that resides on user
storage or a network share has read access to the folder
it resides in and all folders below it. The
vulnerabilities provide methods by which an applet
located on a web site could misrepresent the location of
its codebase, to indicate that it resided instead on the
user's local system or a network share.
- A vulnerability that could enable an attacker to construct
an URL that, when parsed, would load a Java applet from
one web site but misrepresent it as belonging to another
web site. The result would be that the attacker's applet
would run in the other site's domain. Any information the
user provided to it could be relayed back to the attacker.
- A vulnerability that results because the Microsoft VM
doesn't prevent applets from calling the JDBC APIs - a
set of APIs that provide database access methods. By
design, these APIs provide functionality to add, change,
delete or modify database contents, subject only to the
- A vulnerability through which an attacker could
temporarily prevent specified Java objects from being
loaded and run. A legacy security mechanism known as the
Standard Security Manager provides the ability to impose
restrictions on Java applets, up to and including
preventing them from running altogether. However, the VM
does not adequately regulate access to the SSM, with the
result that an attacker's applet could add other Java
objects to the "banned" list.
- A vulnerability through which an attacker could learn a
user's username on their local system. The vulnerability
results because one particular system property, user.dir,
should not be available to untrusted applets but, through
a flaw, is. While knowing a username would not in itself
pose a security risk, it could be useful for
- A vulnerability that results because it's possible for a
Java applet to perform an incomplete instantiation of
another Java object. The effect of doing so would be to
cause the containing application - Internet Explorer - to
All of the vulnerabilities share a pair of common mitigating factors:
- The web-based attack vector would be blocked if the user
had disabled Java applets in the Internet Explorer
security zone in which the attacker's web site rendered.
- The email vector would be blocked if the user were running
any of several mail clients. Specifically, Outlook
Express 6 and Outlook 2002 (which ships as part of Office
XP) disable Java by default, and Outlook 98 and 2000
disable it if the Outlook Email Security Update has been
COM Object Access Vulnerability:
- The vulnerability represents a target of opportunity only.
The attacker would have no means of ensuring that
sensitive data would be located in system memory, cookies,
the clipboard, or other locations.
CODEBASE Spoofing Vulnerabilities:
- The attacker's access to files, including those on remote
shares, would be limited to those of the user. If the
user had only limited permissions, so would the attacker.
Domain Spoofing Vulnerability:
- The vulnerability could only be exploited if the user
visited the attacker's site en route to visiting a
- The effect of exploiting the vulnerability would apply
only to the current web session.
JDBC API Vulnerability:
- To exploit this vulnerability, the attacker would need
to know the names of each data source he or she wanted
to access. In most cases, this would require the attacker
to have insider knowledge of the user's network.
- The attacker would gain only the user's own permissions
to the data sources. For instance, if the user had only
read access to a particular database, so would the
Standard Security Manager Access Vulnerability:
- The effect of exploiting this vulnerability would only
persist during the current browser session.
- The vulnerability provides no means of modifying an
applet's functioning - only preventing it from running.
User.dir Exposure Vulnerability:
- Knowing a user's username would not, by itself, enable
an attacker to take any action against the user. The
sole value in learning this information would be for
reconnaissance purposes, in the hope of using it in
some future, unspecified attack.
Incomplete Java object Instantiation Vulnerability:
- This vulnerability would only enable the attacker to
cause Internet Explorer to fail - it would not enable
the attacker to cause Windows itself, or any other
applications, to fail.
- The user could restore normal operation by restarting
- COM Object Access Vulnerability: Critical
- CODEBASE Spoofing Vulnerabilities: Important
- Domain Spoofing Vulnerability: Moderate
- JDBC API Vulnerability: Moderate
- Standard Security Manager Access Vulnerability: Low
- User.dir Exposure Vulnerability: Low
- Incomplete Java object Instantiation Vulnerability: Low
- A patch is available to fix this vulnerability. Please read the
Security Bulletin at
for information on obtaining this patch.
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