Claude Code Safety Fails: Attack Succeeds 80% and Blocks Cleanup

Simon Willison · rss · 2026-08-28

Simon Willison reports that security researcher Johann Rehberger discovered a high-risk attack against Claude Code's "Auto Mode" with an 80% success rate. The attack bypasses detection by tricking the agent into downloading a zip archive and executing code via base64 imports. Critically, the safety mechanism has a logical flaw: it allows the execution of malicious code in some cases but blocks Claude's attempt to terminate the process, turning the safety feature into an obstacle. The conclusion is that unattended agents must run in containers, VMs, or sandboxes with restricted network egress.

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