The GFW does not verify TCP checksums or validate RST flag combinations: Strategy 5 using the entirely invalid flag set FRAPUN with TTL 10 achieved 96% success. Separately, increasing the TCP data offset (dataofs) field to 10 in an insertion duplicate causes the GFW to reinterpret the beginning of the HTTP payload as TCP header bytes, preventing keyword detection and achieving 98% success (Strategy 2) — while the destination server discards the malformed packet.

Evasion strategies are strongly censor-specific: TCB Teardown strategies that achieve 80–96% against the GFW fail completely (0%) against Kazakhstan's HTTPS MITM; India's Airtel is defeated uniquely by a 'Stutter Request' (duplicating the PSH/ACK and replacing IP length to 64) at 100% success, which scores only 3% against the GFW. Geneva converged on distinct species for each censor within 4–8 hours of live training.

Table 1, §5.1–5.4 evaluation

Geneva, a genetic algorithm using four packet-manipulation primitives (drop, tamper, duplicate, fragment), independently re-derived 30 of 36 (83.3%) previously published evasion strategies in controlled lab experiments and discovered successful strategies in 23 of 27 live training sessions against China's GFW, yielding 4 unique species, 8 subspecies (5 novel), and 21 fundamentally different variants. Each training session ran for 4–8 hours against a real censor.

§5, Abstract defense

Geneva experiments revealed that the GFW determines TCP three-way handshake completion using only the presence of the ACK flag — without validating sequence numbers. Upon receiving a RST or RST/ACK before the handshake completes, the GFW enters a resynchronization state approximately 50% of the time rather than tearing down its TCB; strategies that exploit this pre-handshake window achieve 92–95% success rates (Strategies 3 and 4).

§5.2 Species 2: TCB Teardown detection

Geneva's Segmentation species — fragmenting HTTP requests at the TCP layer without IP fragmentation, segment overlapping, or insertion packets — achieved 94–98% success against the GFW, 100% against India's Airtel ISP, and 100% against Kazakhstan's HTTPS MITM, making it the only strategy class effective across all three tested censors. These strategies require neither raw sockets nor root privilege.

§5.2 Species 3: Segmentation defense

Russian TSPU devices directly block ECH by dropping ClientHello messages that contain both an ECH extension and the outer SNI hostname "cloudflare-ech.com" — the static outer SNI Cloudflare advertises in all its ECH configurations. Blocking affects both TLS and QUIC. ECH connections to servers with Cloudflare ECH support but outside Cloudflare's official IP ranges are NOT blocked. TCP segmentation alone or TLS record fragmentation alone did NOT bypass TSPU ECH blocking, but combining both techniques did circumvent it. TSPU has also added TCP reassembly capabilities that defeat previously effective fragmentation-only bypasses.

2025-niere-encrypted §5, Figure 5 dpirst-injectionmiddlebox-interference

The GFI's HTTP and HTTPS filters are now stateful (requiring initial SYN packet with matching sequence numbers) and have been activated on all TCP ports—not only standard ports 80 and 443 as reported by prior studies. This is a significant departure from previous work that found stateless HTTP/HTTPS blocking limited to standard ports. The HTTP filter injects a 403 Forbidden blockpage (not RST packets as used by the GFW), while HTTPS injects a single RST+ACK packet. The GFI also exhibits TCP non-compliance (not requiring a full three-way handshake to trigger filtering), enabling outside-in measurement without in-country servers.

2025-tai-irblock §2.1, §3.2 dpirst-injectionpacket-injectionmiddlebox-interference

The Henan Firewall is stateless in two exploitable ways: (1) it requires the TCP header to be exactly 20 bytes—enabling any TCP option (e.g., TCP Timestamps, which Windows disables by default) to bypass it entirely; (2) it does not perform TCP reassembly, so splitting a TLS ClientHello across two TCP segments such that the SNI extension straddles the boundary bypasses the censor. Both bypasses require only client-side changes and have already been implemented in Xray, GoodbyeDPI, and Shadowrocket. TLS record fragmentation (splitting the ClientHello across multiple TLS records within one TCP segment) also defeats both the Henan Firewall and the GFW, since neither performs TLS reassembly.

2025-wu-regional-censorship §4.3 / §6 sni-blockingdpimiddlebox-interference

Longitudinal GFWeb data spanning 20 months shows the GFW actively patched previously-published evasion findings during the measurement period: overblocking bugs reported in academic papers were fixed, and fragmented-packet reassembly failures that researchers used to bypass blocking were corrected. This demonstrates that the GFW operator monitors published research and iterates on the system in response to disclosed vulnerabilities.

2024-hoang-gfweb Abstract, §5.4, §6 dpimiddlebox-interference

The SAT Móvil app (Mexico's official tax service, 1M+ downloads) consistently fetches its 'Chat' page over cleartext HTTP, exposing citizen ID numbers (CURP, RFC), passwords, and tax documents to any in-path attacker. None of the four major Latin American telco apps (MiTelcel, MiTigo, MiClaro, MiMovistar) implement HSTS on SMS-delivered external links, making all of them uniformly vulnerable to SSL strip downgrade attacks.

2024-kujath-analyzing §7.2, Table 3 dpimiddlebox-interference

China's Great Firewall showed anomalous inconsistency: 13 test vectors produced mixed outcomes—TCP RST injection on some executions and a clean server response on others—with circumvention rates between 10% and 35% across 100 executions per vector. The authors attribute this to heterogeneous GFW infrastructure components applying different HTTP parsing logic, a departure from the GFW's usual consistency.

2024-m-ller-turning §5.2 dpirst-injectionkeyword-filteringmiddlebox-interference