Apparent Bug (Apache: The Definitive Guide, 3rd Edition)

9.3. Apparent Bug

When a server is set up as a proxy, then requests of the form:

GET http://someone.else.com/ HTTP/1.0

are accepted and proxied to the appropriate web server. By default, Apache does not proxy, but it can appear that it is prepared to — requests like the previous will be accepted and handled by the default configuration. Apache assumes that someone.else.com is a virtual host on the current machine. People occasionally think this is a bug, but it is, in fact, correct behavior. Note that pages served will be the same as those that would be served for any real unknown virtual host on the same machine, so this does not pose a security risk.