A web conferencing operator can enable participants to share multimedia content in real-time despite one or more of the participants operating from behind a middlebox via network address translation (NAT) traversal protocols and tools, such as STUN, TURN, and/or ICE. In NAT traversal, participants share a transport addresses that the participants can use to establish a joint media session. However, connectivity checks during NAT traversal can expose a media distribution device hosted by the web conferencing operator to various vulnerabilities, such as distributed denial of service (DDoS) attacks. The web conferencing operator can minimize the effects of a DDoS attack during the connectivity checks at scale and without significant performance degradation by configuring the middlebox to validate incoming requests for the connectivity checks without persistent signaling between the web conference operator and the middlebox.