Language: Python
Label: safe
CWE: CWE-613 \u2014 Insufficient Session Expiration
According to WASC, "Insufficient Session Expiration is when a web site permits an attacker to reuse old session credentials or session IDs for authorization."

Code:
    def user_exists(self, username):
        """
        Check if a user actually exists in the database.

        :param username:
        :return: boolean
        """
        return self.pyload.db.user_exists(username)