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Microsoft Reports Security Holes in Web Extender Client

Microsoft reported a security vulnerability in the Web Extender Client component of Office 2000, Windows 2000, and Windows Me that would send certain authentication credentials of a user to a malicious third party.

The Web Extender Client (WEC) is a component that ships as part of Office 2000, Windows 2000, and Windows ME. WEC allows IE to view and publish files via Web folders, similar to adding and viewing files in a directory through the Windows Explorer.

Due to an implementation flaw, WEC does not respect the IE Security settings regardint when NTLM authentication will be performed. Instead, WEC will perform NTLM authentication with any server that requests it. If a user established a session with a malicious user’s Web site, an application on the site could capture the user’s NTLM credentials. The malicious user could then use an offline brute force attack to derive the password, or, with specialized tools, could submit a variant of the credentials in an attempt to access protected resources.

The vulnerability would only provide a hacker with the cryptographically protected NTLM authentication credentials of another user. It would not, by itself, allow a malicious user to gain control of another user’s computer or to gain access to resources to which that user was authorized access. In order leverage the NTLM credentials, the malicious user would have to be able to remotely logon to the target system.

A patch to fix this vulnerability is available at Microsoft’s Web site. – Isaac Slepner

About the Author

Scott Bekker is editor in chief of Redmond Channel Partner magazine.

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