Security Bulletin MS02-044 : Unsafe Functions in Office Web Components (Q328130)

2002-08-23T00:00:00
ID SECURITYVULNS:DOC:3407
Type securityvulns
Reporter Securityvulns
Modified 2002-08-23T00:00:00

Description


Title: Unsafe Functions in Office Web Components (Q328130) Date: 21 August 2002 Software: Office Web Components, Office, BackOffice Server, BizTalk Server, Commerce Server, ISA Server, Money, Microsoft Project, Microsoft Project Server Small Business Server Impact: Three vulnerabilities, the most serious of which could allow an attacker to run commands on the user's system. Max Risk: Critical Bulletin: MS02-044

Microsoft encourages customers to review the Security Bulletin at: http://www.microsoft.com/technet/security/bulletin/MS02-044.asp.


Issue:

The Office Web Components (OWC) contain several ActiveX controls that give users limited functionality of Microsoft Office in a web browser without requiring that the user install the full Microsoft Office application. This allows users to utilize Microsoft Office applications in situations where installation of the full application is infeasible or undesirable.

The control contains three security vulnerabilities, each of which could be exploited either via a web site or an HTML mail. The vulnerabilities result because of implementation errors in the following methods and functions the controls expose:

  • Host(). This function, by design, provides the caller with access to applications' object models on the user's system. By using the Host() function, an attacker could, for instance, open an Office application on the user's system and invoke commands there that would execute operating system commands as the user.

  • LoadText(). This method allows a web page to load text into a browser window. The method does check that the source of the text is in the same domain as the window, and in theory should restrict the page to only loading text that it hosts itself. However, it is possible to circumvent this restriction by specifying a text source located within the web page's domain, and then setting up a server-side redirect of that text to a file on the user's system. This would provide an attacker with a way to read any desired file on the user's system.

  • Copy()/Paste(). These methods allow text to be copied and pasted. A security vulnerability results because the method does not respect the "disallow paste via script" security setting in IE. Thus, even if this setting had been selected, a web page could continue to access the copy buffer, and read any text that the user had copied or cut from within other applications.

The patch does not set "kill bit" on the control, for reasons discussed in the FAQ.

Mitigating Factors:

Overall:

  • In the case of the web-based attack, an attacker would need to force a user to visit the attacker's Web site. Users who exercise caution in visiting web sites could minimize their risk.

  • In the web based attack, If ActiveX controls have been disabled in the zone in which the page were viewed, the vulnerability could not be exploited. Users who place untrusted sites in the Restricted Sites zone, which disables ActiveX by default, or have disabled ActiveX controls in the Internet zone could minimize their risk.

  • In the case of HTML email based attacks, customers who read email in the Restricted Sites zone would be protected against attempts to exploit this vulnerability. Customers using Outlook 2002 and Outlook Express 6.0, as well as Outlook 2000 and Outlook 98 customers who have applied the Outlook Email Security Update would thus be protected by default. Also, Outlook Express 5.0 customers who have chosen to read mail in the Restricted Sites zone would be protected by default.

  • In the HTML email based attack, Outlook 2002 customers who have enabled the "Read as Plain Text" option available in SP1 or later would also be protected.

Host() Vulnerability:

  • The attacker's code would be limited by restrictions on the user's account. Users of non-privileged accounts would limit the potential damage from a successful attack.

LoadText():

  • The attacker would need to know the full path and name of the file. In addition the file would have to be viewable in a web browser.

Copy()/Paste():

  • The vulnerability could enable an attacker to access only to information in the Windows clipboard. The information in the clipboard is unpredictable and this vulnerability gives no means for an attacker to target and retrieve specific information. Further, it is possible for the clipboard to be empty, which would yield an attacker nothing.

  • The security setting in question is not enabled by default. Thus, the vulnerability does not present a threat to the default installation.

Risk Rating:

  • Internet systems: Moderate
  • Intranet systems: Moderate
  • 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/ms02-044.asp for information on obtaining this patch.

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