FINDING · DETECTION
Real-world CDN HTTPS deployments leak the identity of visited websites through three distinct channels — TLS certificate contents (A2, B1, B2 deployments), the plaintext SNI field (B1), and dedicated IP address mappings (B2) — enabling censors to block CDNBrowsing connections via standard DPI or IP filtering without collateral damage to non-forbidden CDN content. Each leakage channel requires inspecting only a single packet from an HTTPS connection, making the attack low-cost and deployable on off-the-shelf censorship boxes.
From 2016-zolfaghari-practical — Practical Censorship Evasion Leveraging Content Delivery Networks · §3.1 · 2016 · Computer and Communications Security
Implications
- CDNBrowsing systems must implement per-CDN HTTPS handling (SNI substitution, edge-server selection) rather than a one-size-fits-all approach; at minimum, replace forbidden domain SNI with a non-forbidden domain and avoid dedicated edge-server IP addresses.
- Any proxy-less CDN-based circumvention tool must audit every CDN's HTTPS deployment for certificate, SNI, and IP leakage before relying on it — CloudFlare's strict SNI enforcement makes it unusable against competent DPI-equipped censors.
Tags
Extracted by claude-sonnet-4-6 — review before relying.