When the HTTP stream wrapper follows a redirect and the response carries a Location header with an empty value, the redirect code reads one byte past...

When the HTTP stream wrapper follows a redirect and the response carries a Location header with an empty value, the redirect code reads one byte past the end of the heap buffer holding the location. The value of that out-of-bounds byte decides which redirect target is built, so a malicious server controls whether the client is sent to the host root or to the current directory.