The secure_load function in gluon/utils.py in web2py before 2.14.2 uses pickle.loads to deserialize session information stored in cookies, which might allow remote attackers to execute arbitrary code by leveraging knowledge of encryption_key.
https://usn.ubuntu.com/4030-1/
https://github.com/web2py/web2py/blob/R-2.14.1/gluon/utils.py#L200