The GFW's DNS packet injector (Injector 3, identified by TTL mirroring and zero IP ID) contained an out-of-bounds read vulnerability: due to missing label-length and null-terminator validation, malformed DNS requests caused the injector to copy adjacent stack memory into forged responses. Over three days in October 2023, researchers collected over 1 TB of data containing over 13 billion leaks, ~87.43% with non-duplicate content, including live Internet traffic transiting China's backbone and stack frames of the GFW's packet-handling processes.

The GFW DNS injector vulnerability enabled reflective amplification attacks with a baseline factor of 4.04× (46-byte payload → 186-byte response). Combined with routing loops — approximately 1,000 destination IP addresses in China were found to loop packets across the GFW more than 30 times, with 159 persisting after two days and a maximum of 119 loop iterations per query — the effective amplification factor reached 481.17×, sufficient to generate 100 Gbps of attack traffic from just over 200 Mbps of source traffic.

§5.2 Reflective Amplification Attack evaluation

The GFW patched the out-of-bounds read vulnerability city by city in October–November 2023, updating from least to most international traffic: CERNET/Beijing before October 26, Guangzhou on October 30, and Shanghai in two distinct phases on October 31 and November 1, with all updates occurring around 11 a.m. CST. Shanghai, which terminates the most international submarine cables, was updated last and in two steps to minimize side effects.

§4.5 Maintenance and Update deployment

Automated pattern analysis of 13 billion leaked GFW memory frames found over 52.8 million HTTP/1.x protocol signatures, 984,567 Authorization headers, 1.9 million Cookie headers, 79,090 password-in-URL occurrences, and 59,326 SMTP/IMAP plaintext credential sequences — yielding over 3 million pieces of potentially sensitive data collected at a deliberately limited rate of 5,000 exploit packets per second.

§4.3 Traffic Patterns, Table 2 evaluation

Analysis of leaked stack frames confirmed the GFW's packet injector processes run on x86-64 Linux with ASLR and PIE enabled but without stack canaries, implying that buffer overflow vulnerabilities in the GFW may lack effective mitigation. Each injector process was inferred to use exactly four packet-handling threads, identified by up to four unique stack-address groups per return address (each group spanning within the 8 MB default Linux stack size).

§4.4 Process Characteristics deployment

The GFI operates three distinct DNS/HTTP injectors with different fake IP addresses (10.10.34.34, 10.10.34.35, 10.10.34.36) and partially overlapping blocklists—mirroring the GFW's triplet-censor architecture. Injector 10.10.34.35 exhibits TTL reflection (injected response TTL = probe TTL − hop count), identical to the GFW. No IP exclusively receives injections from 10.10.34.34 (a smaller, selective component); the two primary injectors 10.10.34.35 and 10.10.34.36 handle the majority of censorship. Different injectors maintain distinct domain blocklists, meaning which domains a user sees as censored depends on routing through their AS.

2025-tai-irblock §5.4, Table 2 dns-poisoningpacket-injectiondpi

Analyzing over 3 million OONI network measurements (2016–2020) from 17 ASes covering 98.45% of broadband and 90.94% of mobile subscribers in Spain, the study detected 16 unique blockpages, 2 DPI vendors (Fortinet/Fortigate in Telefonica; Allot in Vodafone), and 78 blocked websites across copyright, political, civil-rights, and referendum categories.

2021-ververis-understanding §3, §4 dpidns-poisoningpacket-injectionsni-blockingmeasurement-platform

Across MENA countries (UAE, Tunisia, Oman, Iran, Qatar, Yemen, Saudi Arabia, Burma), over 80% of blockpage-delivering tests delivered the blockpage without DNS redirection, indicating transparent web proxies performing deep HTTP inspection rather than the cheaper DNS-intercept approach dominant in China. McAfee SmartFilter was identified in Qatar, Saudi Arabia, and UAE; Netsweepr in Qatar, UAE, and Yemen.

2015-gill-characterizing §5.1, Table VI dpipacket-injectiondns-poisoning

Across 11 countries, censorship execution falls into at least six distinct categories: DNS redirect to localhost (Malaysia, Russia, Turkey), DNS redirect with warning page (South Korea), connection timeout with no notification (Bangladesh, India), spoofed TCP RST injection (China), spoofed HTTP 403 with warning page (Bahrain, Iran), HTTP 302 redirect (South Korea, Thailand), and spoofed HTTP 200 iframe response (Saudi Arabia). Four countries censor at DNS and eight at routers, with South Korea employing both layers simultaneously.

2012-verkamp-inferring Table 3 dns-poisoningrst-injectionpacket-injectiondpi

The June 2025 Iran shutdown—carried out during the Iran-Israel war beginning ~June 19—did not use BGP route withdrawals as in 2019. Instead, authorities applied service-level restrictions at the national border: DNS poisoning of foreign destinations, protocol whitelisting permitting only pre-approved domestic services, and DPI to block circumvention-tool traffic. Iran's international traffic fell roughly 90% while the country's BGP routes remained advertised, making the shutdown invisible to BGP-based monitoring systems. OONI measurement volume, which totalled 121,333 in June 2025, collapsed to under 200 submissions on June 19-20.

2025-iran-shutdown-measurement Executive Summary / §2 dpidns-poisoningport-blockingip-blocking

Article 19 documents that Iran's National Information Network (NIN / SHOMA) was designed with explicit reference to China's Great Firewall as a model, with institutional mirroring: Iran's Supreme Council of Cyberspace parallels China's Cyberspace Administration of China, and both governments share a "cyber sovereignty" doctrine used to justify domestic content controls and cross-border technology transfer. The report frames Iran's filtering infrastructure as deliberately architected to replicate GFW capabilities, not as an independently developed system.

2026-article19-tightening-the-net §2, §3 dpisni-blockingdns-poisoningip-blockingbgp-hijackthrottling