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, user):
        self.c.execute("SELECT name FROM users WHERE name=?", (user,))
        return self.c.fetchone() is not None