Title: Malformed Dotless IP Address Can Cause Web Page to be
Handled in Intranet Zone
Date: 10 October 2001
Software: Internet Explorer
Impact: Three vulnerabilities:

• Cause web page to render a web page using inappropriate security
  settings
• Send commands to a third-party web site in the guise of the user
• Create a file on the system of a user who visited a web site.
  Bulletin: MS01-051

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS01-051.asp.

Issue:

This patch eliminates three vulnerabilities affecting Internet
Explorer. The first involves how IE handles URLs that include dotless
IP addresses. If a web site were specified using a dotless IP format
(e.g., http://031713501415 rather than http://207.46.131.13), and the
request were malformed in a particular way, IE would not recognize
that the site was an Internet site. Instead, it would treat the site
as an intranet site, and open pages on the site in the Intranet Zone
rather than the correct zone. This would allow the site to run with
fewer security restrictions than appropriate. This vulnerability does
not affect IE 6.

The second involves how IE handles URLs that specify third-party
sites. By encoding an URL in a particular way, it would be possible
for an attacker to include HTTP requests that would be sent to the
site as soon as a connection had been established. These requests
would appear to have originated from the user. In most cases, this
would only allow the attacker to send the user to a site and request
a page on it. However, if exploited against a web-based service
(e.g., a web-based mail service), it could be possible for the
attacker to take action on the user's behalf, including sending a
request to delete data.

The third is a new variant of a vulnerability discussed in Microsoft
Security Bulletin MS01-015, affecting how Telnet sessions are invoked
via IE. By design, telnet sessions can be launched via IE. However, a
vulnerability exists because when doing so, IE will start Telnet
using any command-line options the web site specifies. This only
becomes a concern when using the version of the Telnet client that
installs as part of Services for Unix (SFU) 2.0 on Windows NT(r) 4.0
or Windows(r) 2000 machines. The version of the Telnet client in SFU
2.0 provides an option for creating a verbatim transcript of a Telnet
session. An attacker could start a session using the logging option,
then stream an executable file onto the user's system in a location
that would cause it to be executed automatically the next time the
user booted the machine. The flaw does not lie in the Telnet client,
but in IE, which should not allow Telnet to be started remotely with
command-line arguments.

Mitigating Factors:

Zone Spoofing vulnerability:

• The default settings in the Intranet Zone differ in only a few
  ways from those of the Internet Zone. The differences are
  enumerated in the FAQ, but none would allow destructive action
  to be taken.
  HTTP Request Encoding vulnerability:
• In order to exploit this vulnerability successfully, the
  attacker would need to possess significant personal
  information about the victim, such as what web services the
  user subscribed to, folder structures, and so forth.
• Even if the attacker knew the requisite personal information,
  factors outside of the attacker's control (such as whether
  the user was logged onto the service already) could cause the
  user to see prompts and dialogues that would indicate that an
  attack was underway.
• It is unlikely that the vulnerability could be used to target
  large populations; it is likely that it could be used only against
  specific targets.
  New variant of Telnet Invocation vulnerability:
• This vulnerability is only a concern for customers who are using
  the Telnet client that ships as part of Services for Unix 2.0.
  No other versions of Telnet contain the command-line feature to
  create log files, including the versions that ship by default
  as part of Windows platforms.

Patch Availability:

• A patch is available to fix this vulnerability. Please read the
  Security Bulletin at
  http://www.microsoft.com/technet/security/bulletin/ms01-051.asp
  for information on obtaining this patch.

Acknowledgment:

• Michiel Kikkert ([email protected])
• Joao Gouviea ([email protected])

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