Iran's fragmentation-detection capability targets the fragmentation mechanism itself, not the SNI field content: testers report blocking occurs even when the fragmented ClientHello carries a clean, non-blocked SNI. This indicates the censor is classifying flows by structural packet properties (fragment boundary patterns) rather than by inspected SNI value.

Iran's censorship infrastructure began dropping all fragmented TLS ClientHello packets around late July 2026, rendering the tlshello fragmentation bypass technique non-functional. The blocking took effect approximately July 27, 2026, based on user-reported timelines in the net4people/bbs community report.

Issue body (Jul 31 2026) detection

Community testing in Iran following the fragmentation bypass failure confirms that REALITY and Shadowsocks remain viable circumvention mechanisms as of late July 2026. Neither protocol relies on ClientHello fragmentation for evasion, which accounts for their continued functionality under the updated Iranian filtering regime.

Abstract / issue comments evaluation

TSG's Context-Based Detector (CBD) evaluates circumvention tool signatures across JA3/JA4 TLS fingerprints, SSL certificate issuer fields, UDP payload length, first-packet byte patterns, server IP ranges, and FQDN matches, often combining multiple conditions with logical AND. Of 29 VPN and circumvention tool signatures logged in the VPN Signature File Update Log (March–November 2024), 21 carry risk level 5 (the maximum), indicating aggressive prioritization of blocking major tools including ExpressVPN, NordVPN, Tor Browser, and Psiphon.

2026-ablove-technical-analysis-geedge §4.1, §4.1.2, Table 3, Table 4 dpitls-fingerprinttraffic-shapeip-blockingsni-blocking

The paper identifies a fundamental architectural vulnerability in single-IP circumvention designs: a relay must generate new observable flows (via DNS or TLS SNI) to reach end services after receiving client connections, creating a detectable server-and-client behavioral contrast. A relay accessing user-facing domains (news, social media) scores high on a Relay Suspicion Score (w=0.9) versus infrastructure domains (w=0.1). The paper argues this host-level signal is censorship-invariant and cannot be concealed by link obfuscation.

2026-almutairi-server §2.4, §4 traffic-shapedpisni-blocking

Iran's DPI infrastructure performs full TCP reassembly and stateful inspection on the fly, nullifying TCP fragmentation (10–30 byte fragments with 10–20ms delays) applied to VLESS+WebSocket behind Cloudflare CDN in full-strict mode. Domains are blocked within 24 hours despite the CDN layer and rotation of clean Cloudflare IPs. Fragmentation was applied to the first 5 packets and verified correct on the client side with tcpdump; the setup used port 443 with a randomized WebSocket path.

2026-pooribitwise-iran-advanced-dpi Issue body — Description / The Issue dpisni-blockingtraffic-shape

Amnesty International's 102-page investigation identifies a multi-vendor surveillance stack deployed in Pakistan: Chinese DPI (Geedge/MESA-derived), Canadian social-media monitoring (Netsweeper), and Emirati commercial spyware (Pegasus and FinFisher). The system enables deep packet inspection, SNI-based filtering, and traffic-shape classification at national scale, including targeted interception of encrypted messaging apps and VPN traffic.

2025-amnesty-pakistan-shadows §3, §5 dpisni-blockingip-blockingtraffic-shapeml-classifier

Internal Geedge documents confirm active contracts to deploy GFW-derived censorship and surveillance infrastructure in Myanmar, Pakistan, Ethiopia, Kazakhstan, and at least one additional unidentified country under the Belt and Road framework, in addition to domestic deployments in Xinjiang, Jiangsu, and Fujian. The exported product (the Tiangou Secure Gateway / TSG line) is not a stripped-down export variant — leaked TSG documentation shows DPI, active-probing, ML classifiers, and granular per-region traffic control rules that mirror the domestic GFW capability set.

2025-geedge-mesa-leak §5, §6 dpiactive-probingml-classifiersni-blockingdns-poisoningfully-encrypted-detecttraffic-shape

InterSecLab's 76-page analysis of the Geedge/MESA leak (based on nine months of indexing and translating >100,000 documents) characterizes the Tiangou Secure Gateway (TSG) product line as a commercially deployable detection stack that combines deep packet inspection, real-time mobile subscriber monitoring, active probing, ML-based traffic classifiers, and granular per-region rule sets. TSG is not a research prototype — leaked documentation includes deployment timelines and client government interactions for Kazakhstan, Ethiopia, Pakistan, Myanmar, and one unnamed country, with censorship rules explicitly tailored to each region.

2025-interseclab-internet-coup §3–§5 (InterSecLab report) dpiactive-probingml-classifiersni-blockingip-blockingtraffic-shapefully-encrypted-detect