In a recent application security audit for a web-site I came across a big, blaring breach. while it's always fun to find a good vulnerability, it turned out to be quite tricky to actually exploit it. The trickiness was not due to good security practices but to pure (un)luck (depending on whose point of view). It seemed every angle I tried was off by just a tiny bit. Eventually I managed to find an interesting multiphase exploit vector, and I think it makes for some interesting tinkering/reading.  I've created a mock-up replica of the vulnerable web-site to allow for testing and analysis. After reading the vulnerability introductory section you may wish to try your wit against the mock-site and find it yourself, before reading on to the detailed exploit write-up. Write up here: http://blog.quaji.com/2011/02/tricky-exploit-penetration-test-puzzle.html Ronen Zilberman