Exploiting Common Vulnerabilities in PHP Applications

This paper is based on a speech given during the Blackhat briefings in Singapore
and Hong Kong in April 2001. The speech was entitled "Breaking In Through
the Front Door - The impact of Web Applications and Application Service
Provision on Traditional Security Models". It initially discussed the trend
towards Web Applications (and ASP) and the holes in traditional security
methodology exposed by this trend.
Definetely a good read -- check it all out here.