Support for UDP over SOCKS5 (QUIC / HTTP/3)

Modern web services are actively transitioning to HTTP/3, which operates over QUIC, and QUIC operates over UDP.

For browser platforms, this means the need for full routing not only of TCP traffic but also UDP connections through proxies.

If UDP does not pass through the proxy tunnel, network mismatches occur, and in certain cases, there is a risk of leaking the real IP address.

Why UDP support is critically important

A browser can:

• declare support for HTTP/3
• use a modern TLS stack
• correctly generate a fingerprint

But if QUIC is not routed through the proxy, one of the following occurs:

• HTTP/3 is not established
• the connection is forcibly downgraded to HTTP/2
• UDP traffic goes directly

For modern anti-fraud systems, this is an indicator of network anomaly.

Architectural approach

A comprehensive implementation includes:

• support for the SOCKS5 UDP ASSOCIATE mechanism
• transmission of QUIC datagrams through proxy IP
• correct establishment of HTTP/3 without fallback
• coordinated operation with the Chromium network stack

As a result, the server sees the proxy IP for all traffic — both TCP and UDP.

Technical routing scheme (Packet Flow)

Below is a simplified diagram of QUIC traffic passing through SOCKS5:

Process Details

1. The browser establishes a TCP connection with the SOCKS5 proxy
2. The UDP ASSOCIATE command is executed
3. The proxy allocates a UDP port for datagram transmission
4. QUIC packets are transmitted through this UDP channel
5. The target server receives traffic from the proxy IP

This architecture eliminates:

• direct UDP traffic bypassing the proxy
• forced downgrade of HTTP/3
• network behavior mismatches

Practical Benefits

• Consistency of network profile
• Realistic behavior of a modern browser
• Correct HTTP/3 handshake
• Absence of IP leaks through UDP
• Increased resilience to network checks

Technological Complexity

Historically, SOCKS5 has been oriented towards TCP connections. Support for UDP requires:

• separate handling of datagram packets
• correct routing without NAT conflicts
• synchronization with the QUIC stack
• integration at the browser's network architecture level

This is a system-level task that requires deep work with the network stack.

Conclusion

Support for UDP over SOCKS5 is a mandatory element of a modern browser platform working with HTTP/3.

Full routing of QUIC traffic through a proxy ensures network integrity, realistic network behavior, and protection against IP leaks.

Afina Browser implements this at the engine level.
No workarounds. No traffic bypass. No protocol degradation.

QUIC traffic is routed correctly through the proxy stack, preserving HTTP/3 functionality while maintaining strict network isolation.

Modern protocol support should not be optional — it should be native.

Afina delivers exactly that.

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