Because Ultrasurf is a single-hop proxy where client ingress and remote web-server egress share the same IP address, any web server contacted through the network can log and report the proxy IP. The paper notes an attacker running a popular web server for a short time would passively harvest the full set of Ultrasurf server addresses for subsequent IP-list blocking.

BlueCoat's commercial DPI hardware/software, deployed in Syria, was confirmed capable of detecting and blocking Ultrasurf connections. BlueCoat logs recovered from Syria additionally exposed real Ultrasurf user behavior, including unproxied traffic leaking to non-Ultrasurf servers before and after bootstrapping completed.

Abstract, §5.8, §6.8 evaluation

An attacker with DNS spoofing capability — the paper cites the GFW explicitly — can respond to Ultrasurf DNS discovery queries before legitimate resolvers and inject crafted CNAME records that fully control the client's single-hop path selection. In code paths where peer verification is skipped ('SkipverifyQ0' log entries), this enables complete traffic interception without any cryptographic break.

§6.4, §5.6 detection

Ultrasurf confirmed to the researcher that its protocol has no forward secrecy and uses RC4 without any integrity check (no MAC or HMAC). This means all recorded ciphertext can be retrospectively decrypted once a session key is recovered, and the stream is trivially malleable — both properties confirmed by the UltraReach team during disclosure.

§8.1, §5.15 defense

Ultrasurf's DNS bootstrapping phase uses subdomain names that are always exactly 16 characters between delimiters and exclusively target .info TLDs, producing a constant byte-width network signature. The paper concludes that filtering this bootstrapping traffic is straightforward even without reverse engineering the client binary, as the client itself acts as a network discovery oracle for censors observing its connections.

§5.6, §6.8 detection

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

Chinese users treat full proxy/VPN (Shadowsocks, V2Ray/Clash, commercial VPNs) as the '终极大杀器' (ultimate solution) for bypassing GitHub DNS poisoning, implying that lighter-weight DNS-only fixes fail in some network environments where the censor adds firewall-layer blocking beyond DNS.

2026-anon-6-github-dns §3 使用代理或 VPN dns-poisoningip-blocking

Rule-based proxy tools (Clash, Shadowsocks, V2Ray) are documented as the most reliable solution for accessing GitHub from China, with split-tunneling rules routing only GitHub traffic through the proxy while keeping domestic traffic on the direct path. Git command-line tools require explicit proxy configuration (git config --global http.proxy http://127.0.0.1:7890) to route clone/push operations, as they do not inherit system proxy settings automatically.

2026-anon-github-2026-6-dns §方法二 dns-poisoningip-blocking

The GFW blocks GitHub via DNS poisoning across at least four domains — github.com, assets-cdn.github.com, github.global.ssl.fastly.net, and raw.githubusercontent.com — causing connection timeouts and page-load failures for mainland China users. The block is persistent as of February 2026, affecting both browser access and command-line git operations.

2026-anon-github-2026-6-dns Introduction / §方法一 dns-poisoningip-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