The ISAPI extension in BadBlue 1.7 through 2.2, and possibly earlier versions, modifies the first two letters of a filename extension after performing a…

The ISAPI extension in BadBlue 1.7 through 2.2, and possibly earlier versions, modifies the first two letters of a filename extension after performing a security check, which allows remote attackers to bypass authentication via a filename with a .ats extension instead of a .hts extension.