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Title: Unchecked Buffer in Internet Explorer and Office for
Mac Can Cause Code to Execute (Q321309)
Date: 16 April 2002
Software: Microsoft Internet Explorer 5.1 for Macintosh, Microsoft
Outlook Express 5.0 for Macintosh, Microsoft Office v. X,
for Macintosh, Microsoft Office 2001 for Macintosh,
Microsoft PowerPoint 98 for Macintosh
Impact: Run Code of Attacker's Choice
Max Risk: Critical
Bulletin: MS02-019

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS02-019.asp.

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Issue:

This is a cumulative patch that, when applied, eliminates all
previously released security vulnerabilities affecting IE 5.1 for
Macintosh, and Office v. X for Macintosh. In addition, it eliminates
two newly discovered vulnerabilities.

• The first is a buffer overrun vulnerability associated with the
  handling of a particular HTML element. Because of support for
  HTML in Office applications, this flaw affects both IE and Office
  for Macintosh. A security vulnerability results because an
  attacker can levy a buffer overrun attack against IE that attempts
  to exploit this flaw. A successful attack would have the result of
  causing the program to fail, or to cause code of the attacker's
  choice to run as if it were the user.

• The second is a vulnerability that can allow local AppleScripts
  to be invoked by a web page. This vulnerability can allow locally
  stored AppleScripts to be invoked automatically without first
  calling the Helper application. The AppleScripts would run as if
  they had been launched by the user, and could take the same
  actions as any AppleScript legitimately launched by the user.
  The AppleScript would have to already be present on the system;
  there is no way for an attacker to deliver an AppleScript of her
  choosing through this vulnerability.

Mitigating Factors:

Unchecked Buffer in HTML Element:

• Successfully exploiting this issue with Office files requires
  that a user accept files from an unknown or untrusted source.
  Users should never accept files unknown or untrusted sources.
  Accepting files only from trusted sources can prevent attempts
  to exploit this issue.

• A successful attack using HTML email would require specific
  knowledge of the user's mail client and cannot be mounted against
  PC users.

• A successful attack using an HTML web page would require the
  attacker to lure the user to visiting a site under her control.
  Users who exercise caution in their browsing habits can
  potentially protect themselves from attempts to exploit this
  vulnerability.

• On operating systems that enforce security on per-user basis,
  such as Mac OS X, the specific actions that an attacker's code
  can take would be limited to those allowed by the privileges of
  the user's account.

Local AppleScript Invocation:

• The vulnerability only affects IE on Mac OS 8 & 9.

• A successful attack requires that the attacker know the full path
  and file name of any AppleScript they want to invoke.

• The vulnerability provides no means to deliver an AppleScript of
  the attacker's construction: it can only invoke AppleScripts
  already present on the user's system.

Risk Rating:

• Internet systems: None
• Intranet systems: None
• 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/ms02-019.asp
  for information on obtaining this patch.

Acknowledgment:

• Josha Bronson of AngryPacket Security
  (http://sec.angrypacket.com/) and w00w00
  (http://www.w00w00.org/).

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