STUN comprehension-optional attributes as a covert channel: Design, implementation, and detection

Researchers discovered that STUN (Session Traversal Utilities for NAT, a protocol that helps devices communicate through network firewalls) can be misused as a covert channel by hiding secret data in optional message attributes that receivers can ignore. The study describes how this attack works, shows a working proof-of-concept implementation, and presents methods to detect when STUN is being used this way.