Cross site scripting (XSS):
References:
- Level 1 - https://www.exploit-db.com/papers/13646/
- Level 2 and for Stored XSS -
- <img src="http://inexist.ent" onerror="javascript:alert(1)"/>
For practice:
- https://xss-game.appspot.com/level2
- Answers: http://blog.dornea.nu/2014/06/02/googles-xss-game-solutions/