Cable networks are complex systems that have evolved over years and in which new features like Internet access and Voice over IP (VoIP) have been integrated. We argue that threat models must evolve together with such systems and show that inadequate threat models can be used to explain known and unknown vulnerabilities in today’s cable networks. We do this by demonstating an attack on the DOCSIS provisioning standard in cable networks. By exploiting this weakness, an attacker can hijack VoIP accounts. We also show how to mitigate the attack.