Researcher Breaks Claude Code Opus 5 Auto Mode with 80% Attack Success Rate
wunderwuzzi23 · x · 2026-08-28
A researcher published a detailed write-up demonstrating a successful code execution attack against Claude Code Opus 5 in Auto Mode, achieving a 60-80% success rate.
Key Facts:
- Context: Anthropic's commissioned evaluation claimed a 0.00% success rate for indirect prompt injection attacks against Opus 5 in Auto Mode, which replaces human approval with a safety classifier.
- Attack Vector: The attack chain involves nudging Claude to use curl instead of the WebFetch tool, redirecting to a specially crafted ZIP archive, and tricking the model into writing and running a Python decoder within an attacker-controlled directory.
- Conclusion: The post argues that Auto Mode is not a substitute for running agents in an isolated environment with active monitoring, revealing limitations in model-only defense layers.
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