Probing 43,842 open recursive resolvers across 173 countries found 26.41% (11,579) suffer some collateral damage from Chinese DNS injection, distributed across 109 countries. The top-affected regions are Iran (88.20%), Malaysia (85.34%), South Korea (79.20%), Hong Kong (74.63%), and Taiwan (66.13%).

DNSSEC validation naturally prevents DNS injection collateral damage: both .de and .kr sign their results, allowing a validating resolver to reject the unsigned injected reply while awaiting the legitimate signed response. The paper identifies DNSSEC deployment at the TLD level as the most robust structural defense against injection-based collateral damage.

§5 defense

DNS injection collateral damage arises from three structural properties of DNS: iterative resolution (full queries sent to root and TLD authorities), anycast routing (two resolvers may reach different physical servers via different paths), and dynamic routing through censored transit ASes. A single domain lookup may generate many queries at multiple levels, any of which can be intercepted by a censored transit AS even when both the originating resolver and the authoritative server are outside the censored network.

§3 detection

TraceQuery probing identified 3,120 router IPs performing DNS injection belonging to exactly 39 Chinese ASes. AS4134 (Chinanet) alone accounts for 1,952 router IPs (62.6% of injecting routers); the top 5 ASes account for over 77% of all identified injecting routers.

§4.2, Table 3 evaluation

TLD-level paths are the primary collateral-damage vector: 11,573 resolvers (26.40%) suffered collateral damage via censored transit to TLD authorities, while only 1 resolver (0.002%) was affected via paths to root servers. The .de ccTLD was most affected because a large fraction of US-to-Germany transit traverses Chinese networks.

§4.3, §4.4, Table 6 evaluation

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

Article 19 documents that Iran combines technical filtering with formal coercion of major foreign platforms (including Telegram, Instagram, and WhatsApp) to comply with content removal orders under threat of full blocking. The report notes that Iran's 2022 Women Life Freedom protests accelerated platform blocking when foreign operators refused compliance, demonstrating that the censorship system operates in two modes: coerce-and-allow for compliant platforms, block for non-compliant ones. Domain fronting via these platforms is therefore subject to sudden revocation if political conditions change.

2026-article19-tightening-the-net §6 ip-blockingdns-poisoningthrottling

Both Firefox and Chromium leak cleartext DNS before establishing encrypted DNS connections: they first send an unencrypted UDP DNS query to resolve the DoH server's domain (e.g., doh.opendns.com). An in-path censor can intercept and poison this initial query, making encrypted DNS in browsers completely ineffective without additional circumvention of the resolver-lookup step. Additionally, Chromium always includes the SNI extension in the encrypted DNS TLS handshake (e.g., "doh.opendns.com"), leaking the resolver identity even after the initial lookup. No resolver requires SNI to be present for certificate validation when the resolver's IP certificate is configured.

2026-lange-towards §2.4, §7, §10 dns-poisoningsni-blocking

DNS censorship of encrypted protocols is inconsistent in both China and Iran. In China, Yandex resolvers are censored only when the SNI extension is present; omitting SNI bypasses censorship for these resolvers. In Iran, DoH requires SNI omission for Quad9, Google, Adguard, CleanBrowsing, and NextDNS resolvers, but works with SNI for Yandex and Cisco resolvers. These inconsistencies suggest resolvers have been accidentally missed by censors, highlighting the value of automated tools that trial all resolver-mode combinations rather than hard-coding a single strategy. The support evaluation found 47 resolvers supporting DoH, 16 supporting DoH3, and only 8 supporting DoQ out of ~65 tested.

2026-lange-towards §6.2, Table 2 dns-poisoningsni-blockingip-blocking

DPYProxy-DNS tested 8 circumvention modes against DNS censorship from vantage points in Iran (AS201295, Mashhad) and China (AS4837, China Unicom). In Iran, DoQ was entirely uncensored even with the SNI extension present; DoH3 worked for all Cloudflare and NextDNS resolvers. Iran's censor operates in-path (not on-path like the GFW), making the "Last Response" mode (wait 3s for the last UDP reply) ineffective in Iran but highly effective in China. Auto-mode averaged 12.32s (median 8.28s) in Iran and 13.78s (median 12.90s) in China to discover a working combination.

2026-lange-towards §6.2, §6.3 dns-poisoningsni-blockingip-blocking