HTTP/3

From UDP Probe to Working Tunnel: Analyzing Hysteria2 Behavior via QUIC, HTTP/3 and Client Events

A detailed technical study examined how commercial Hysteria2 VPN endpoints respond to different levels of network probing, starting from simple UDP packets and progressing to full QUIC handshakes and authenticated client connections. The research used custom NetProbe tools on Windows and Linux to test real subscription endpoints, capturing both external probe results and decrypted traffic from an instrumented Hysteria2 client. Simple UDP probes received no response and timed out, while properly formed QUIC Initial packets with TLS ClientHello and ALPN h3 successfully completed handshakes using TLS 1.3 and TLS_AES_256_GCM_SHA384. An unauthenticated HTTP/3 GET request triggered immediate connection closure with H3_NO_ERROR (code 0x100), whereas a legitimate client sending POST /auth with Hysteria-Auth headers received the expected 233 status confirming authentication and UDP forwarding support. Subsequent data transfer tests, including parallel requests and file downloads, were observed inside separate QUIC streams after authentication, confirming that the tunnel carried real traffic. The study highlights differences between external probing and authenticated client behavior, providing practical insight into how Hysteria2 servers handle reconnaissance versus legitimate VPN usage.

UDP Proxies and QUIC Protocol: How Real IP Addresses Leak Through Anti-Detect Browsers

Anti-detect browser users relying on UDP-capable proxies face a hidden risk of real IP leakage when the browser fails to properly route UDP traffic. The QUIC protocol, which powers HTTP/3, runs over UDP and enables features like 0-RTT handshakes, independent streams, and connection migration that can bypass proxy routes. WebRTC connections using ICE, STUN, and TURN further increase exposure because they often attempt direct UDP paths outside the configured SOCKS5 proxy. Without deep network stack control such as TUN interfaces or socket interception, browsers may send WebRTC and QUIC packets through the host's real network interface. Aurorium Browser claims to solve this by natively supporting UDP proxying so that both QUIC and WebRTC traffic stays inside the tunnel. The article stresses that simply disabling WebRTC or forcing HTTP/2 fallback is insufficient and can itself create detectable anomalies for anti-fraud systems.