Affected: Eclipse Foundation NetX Duo

The NetX Secure DTLS server sends a HelloVerifyRequest carrying a freshly generated cookie, but never checks the cookie a client returns. The ClientHello parser copies the client's cookie bytes over the value the server issued, and the server then decides whether the client has been verified from the cookie's length alone. A peer that puts any single cookie byte in its first ClientHello skips the verification exchange entirely, so the server has no return-routability check and completes handshakes for forged source addresses.