Microsoft Reports Security Holes in Web Extender Client
- By Scott Bekker
- January 12, 2001
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
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
Scott Bekker is editor in chief of Redmond Channel Partner magazine.