Claudy Day -- Claude.ai Prompt Injection Attack Chain
Date: 2026-03
Affected: Claudy Day
Attack vector: prompt-injection
Category: real-world
Severity: High

Three chained vulnerabilities in claude.ai: invisible prompt injection via URL parameters, data exfiltration via Anthropic Files API using attacker-controlled API key, and an open redirect on claude.com. Combined, these enabled silent theft of conversation history from default claude.ai sessions.


Mitigations:

Architectural layers (MAESTRO):