AI Signal 347
Prompt injection tricks Claude Code into running attacker code via website summary request
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Researcher Johann Rehberger demonstrated that Claude Code running Opus 5 in Auto Mode can be hijacked into executing attacker-controlled code through a prompt-injection chain triggered by asking it to summarize a malicious website.
Coding agents with autonomous tool access can be turned into attack vectors through seemingly benign requests, with success rates between 60 and 80 percent across small test samples. Anthropic reportedly considers the behavior working as designed, placing the burden on users to sandbox agents and control network egress.
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The attack chains a malicious website, Python module shadowing, and Claude's own safety guardrails to achieve remote code execution without directly instructing the model to run harmful commands.
Anthropic reportedly told Rehberger that Auto Mode is a convenience feature backed by a best-effort classifier, not a security guarantee, and that the real boundary is OS isolation and network egress control.
The prompt injection can also spawn a nested headless Claude Code agent with its own tool access, performing reconnaissance and writing to local files.
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