How I tricked Claude into leaking your deepest, darkest secrets
- ID
- 4903
- Status
- summarized
- Published
- 15 Jul 2026, 10:21 PM
- Fetched
- 15 Jul 2026, 11:25 PM
- Provider
- Simon Willison
- Category
- developer-ai
- Original URL
- https://simonwillison.net/2026/Jul/15/claude-web-fetch-exfiltration/
- Source URL
- https://simonwillison.net/atom/everything/
Summary
- Score
- 8.5
- Created
- 15 Jul 2026, 11:26 PM
- Tags
- Audience
- developersai_agent_userssaas_founders
What happened
Simon Willison details a data exfiltration vulnerability in Anthropic's Claude web_fetch tool discovered by Ayush Paul. The exploit used a honeypot site with nested links to trick the AI into revealing private user information like name, location, and employer. Anthropic has since patched the issue by preventing web_fetch from navigating to additional links found within fetched content.
Why it matters
For developers and founders building AI agents, this highlights the persistent risks of prompt injection and the 'lethal trifecta' where an LLM with private data and web access can be manipulated. Understanding these attack vectors is crucial for designing secure tool-use boundaries in AI applications.
Discussion angle
How to design deterministic guardrails for AI tools to prevent indirect prompt injection and data exfiltration attacks.