Seven Deadliest Web Application Attacks

Inadequate Randomness

Random numbers play an important role in Web security. Session tokens, the cookie values that uniquely identify each visitor, must be difficult to predict. If the attacker compromises a victim's session cookie, then the attacker can impersonate that user without much difficulty. One method of compromising the cookie is to steal it via a network sniffing or cross-site scripting attack. Another method would be to guess the value. If the session cookie were merely based on the user's e-mail address, then an attacker needs only to know the e-mail address of the victim. The other method is to reverse engineer the session cookie algorithm from observed values. An easily predictable algorithm would merely increment session IDs. ...