Inadequate implementation of telecom standards, supply chain threats, and weaknesses in systems architecture could pose major cybersecurity risks to 5G networks. The report cites the contribution of adversarial nations to the development of technical standards, which may pave the way for adopting untrusted proprietary technologies and equipment that could be difficult to update, repair, and replace. Also of concern, per the report, are the optional security controls baked into telecommunication protocols, which, if not implemented by network operators, could leave the door open to malicious attacks.
Source: https://thehackernews.com/2021/05/us-intelligence-agencies-warn-about-5g.html