Microsoft Internet Security and Acceleration (ISA) Server 2006 Gold and SP1, when Radius OTP is enabled, uses the HTTP-Basic authentication method, which allows remote attackers to gain the privileges of an arbitrary account, and access published web pages, via vectors involving attempted access to a network resource behind the ISA Server, aka "Radius OTP Bypass Vulnerability."
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A5649
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2009/ms09-031
http://www.vupen.com/english/advisories/2009/1889
http://www.us-cert.gov/cas/techalerts/TA09-195A.html