Evaluating Practical Enumeration and Blocking Attacks on the Snowflake Circumvention System
Ethical measurements enumerated 21,000+ Snowflake proxy IPs across ~1,000 ASes; blocking top 1% of ASes disrupts 30% of Snowflakes.
Researchers tested Snowflake's assumptions that proxy IPs cannot be easily enumerated and that blocking them causes unacceptable collateral damage. Over 48 days of real-world measurements (May-June 2025), malicious-client-style enumeration collected over 21,000 unique proxy IPs across almost 1,000 autonomous systems. Blocking the top 1% of ASes blocks more than 30% of observed Snowflakes while affecting about 2.5% of Tranco Top 1M domains, and the broker's load-aware matching leaks stable high-capacity proxies to attackers. Some proposed mitigations have already been integrated into Snowflake.
- Enumerated 21,000+ unique proxy IPs across almost 1,000 autonomous systems
- Blocking top 1% of ASes blocks 30% of Snowflakes with ~2.5% Top 1M collateral
- Broker's load-aware matching exposes high-capacity proxies to attackers early
- Higher proxy churn significantly reduces blocking effectiveness in simulation
From the original article
1 min read at arxiv.orgProxy-based Internet censorship circumvention tools like Snowflake rely on large, dynamic pools of third-party proxies to resist IP-based blocking. We focus on two assumptions underpinning the security of Snowflake: that adversaries cannot easily enumerate proxy IPs, and that blocking those proxies would incur unacceptable collateral damage.
By Linden Chen · arxiv.org
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