In HTTP tests, more than 50% of filter responses that indicated censorship contained an injected HTML blockpage; the remainder used TCP RST injection or connection timeout. In HTTPS measurements, canonical template matching had a failure rate of only 1.9%, and 95% of Hyperquack measurements completed within 3.5 hours across ~45,000 vantage points.

Anonymization and circumvention tools (VPNs, Tor, etc.) are among the three most commonly blocked content categories across all commercial filters surveyed, alongside pornography and gambling. This holds across diverse products including Fortinet, Cisco, and government-deployed firewalls in Iran, Saudi Arabia, and Bahrain.

§V-A-1, Fig. 7 evaluation

FilterMap identified 90 blockpage clusters from 90 vendors and actors across 103 countries using 374 million measurements from ~45,000 vantage points against 18,736 sensitive domains; 87 of these signatures were previously unknown. Commercial filters were detected in 36 out of 48 countries rated 'Not Free' or 'Partly Free' by Freedom House, with Fortinet alone present in at least 60 countries.

§V deployment

The Great Firewall of China does not inject blockpages — it resets connections via TCP RST injection — making it invisible to blockpage-based detection systems. In contrast, the Iran firewall accounted for 97.1% of disruptions observed in Iranian vantage points, and the Bahrain and Saudi Arabia firewalls caused 71.2% and 80.2% of disruptions respectively, all using application-layer blockpage injection.

§V-A-2 detection

Russia operates the most fragmented ISP-level filtering infrastructure in the dataset: FilterMap detected 41 distinct ISPs deploying blockpage-injecting filters, and 38 out of 49 filter clusters identified by Quack were deployed in Russian ISPs. All 41 Russian blockpages explicitly cited Federal Law as the reason for blocking.

§V-A-3 deployment

The largest single source of censored domains in the GNL is MESA lab's SNI monitoring dataset (E21-SNI-Top200w.txt) containing 57,362 censored domains, and E21-SNI-Top120W-20221020.txt with 36,467 domains—totaling over 93K domains from network tap data alone for a single country (E21 = Ethiopia per InterSecLab attribution). A separate Xinjiang dataset (XJ-CUCC-SNI-Top200w.txt) contains 13,604 domains. These datasets "do not seem to come from popular domain lists, and instead appear to be gathered from network taps," confirming that Geedge builds censorship target lists directly from passive traffic observation.

2026-sheffey-geedge §4.2, Table 3 dpisni-blockingmeasurement-platform

Of 6,915,266 domains extracted from the 572 GiB Geedge Networks Leak (GNL), 298,955 censored domains (93.7% of all GNL-censored domains) appear in neither Tranco top-1M nor CitizenLab test lists. Measurements across China (Guangzhou/Nanjing), Myanmar, Pakistan, and Algeria confirmed censorship via DNS injection and SNI-based TLS connection termination. The GNL covers 25–62% of Tranco-censored domains across countries, showing substantial but incomplete overlap. This vendor-side ground truth reveals a censorship surface roughly two orders of magnitude larger than curated academic test lists.

2026-sheffey-geedge §4.1, Table 2 dpisni-blockingdns-poisoningmeasurement-platform

TLS connections to blocked services (instagram.com, telegram.org) were terminated by TCP RST immediately after the client's ClientHello, before any certificate exchange, confirming SNI-based DPI that reads the plaintext SNI extension and aborts the handshake. HTTP filtering additionally matched Host headers and URL keywords case-sensitively, with injected HTTP 403 pages or TCP RST responses, and case-change evasions were sometimes effective.

2025-aryapour-stealth-blackout §4.2, §4.3 sni-blockingdpirst-injectionkeyword-filtering

TSPU devices perform in-line packet manipulation — they can inject RST packets, drop traffic, and throttle connections — rather than routing traffic to an out-of-band sniffer that votes to block. The inline placement means TSPU can act on the first-packet payload and impose latency on all matching flows, not only on those selected by sampling. Blocking decisions are therefore applied with high recall at the ISP edge, and circumvention tools that rely on short observation windows (e.g. only obfuscating the first N bytes) are vulnerable to continued inline inspection of subsequent traffic.

2024-xue-tspu-russia §3–§4 dpirst-injectionthrottlingsni-blocking

Censoring middleboxes predominantly use RST injection rather than in-path packet dropping because injecting forged RST/RST+ACK packets does not require the middlebox to sit in the data path — off-path copies of packets suffice. The GFW specifically injects both RST and RST+ACK packets simultaneously after an offending PSH, a known idiosyncratic signature, while Iran's censor uses post-handshake RST injection (⟨SYN;ACK→RST⟩) and packet drops at the same stage.

2023-raman-global §2.1, §4.1 rst-injectiondpisni-blocking

Over 7 months of Hyperquack measurements across 5,555,298 probes targeting 1,632 unique ASes, only a small number of ASes actively interfered with HTTPS connections to FCM endpoints. The majority of blocking incidents occurred in China during September 22–30, 2022, coinciding with the Party's National Congress, when nearly all measurements failed with TCP reset.

2023-xue-use §5.1, Figure 4 sni-blockingrst-injectionmeasurement-platform