TCP segment splitting and out-of-order delivery evades DPI classification in the testbed, T-Mobile, and Iran, but fails against the GFC—which performs extensive packet validation and correctly reassembles reordered streams—and AT&T, which uses a transparent HTTP proxy that normalizes all traffic before inspection. Payload splitting to one byte in the first packet is sufficient to defeat packet-count-limited classifiers.

Middlebox classification state is ephemeral: the testbed carrier-grade DPI device flushes results after 120 seconds (or 10 seconds after a TCP RST), and the GFC flushes state after 40–240 seconds depending on time of day. A strategically timed pause before the matching payload, or a TTL-limited RST packet, causes the classifier to re-evaluate the connection as unclassified traffic.

§4.3, §5.3 detection

Iran's censor and AT&T's Stream Saver restrict DPI inspection strictly to port 80; traffic on any other TCP port escapes classification entirely. Iran additionally inspects the full flow (not just initial packets), unlike T-Mobile and the testbed device which only inspect the first few packets, making packet-count-based evasion insufficient against Iran on port 80.

§1 (key findings), §6.3 detection

lib·erate's TTL-limited inert packet insertion—sending a decoy packet with TTL set to expire at the middlebox but carrying a misclassifying payload—successfully evades classification in a carrier-grade testbed DPI device, T-Mobile's Binge On, and the Great Firewall of China, but fails against Iran's censor and AT&T (Table 3). When bilateral server support is available, inserting a single dummy packet at flow start evades classification in all four deployments.

§4.3, Table 3 evaluation

None of the operational networks tested—T-Mobile, AT&T, the Great Firewall of China, and Iran—classify UDP traffic; the authors describe this as 'a surprisingly easy way to evade their policies.' Iran's censor inspects the entire TCP flow but leaves UDP flows untouched across all tested applications.

§1 (key findings), §6 detection

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