As Simon Willison notes, the core revelation here is less about the specific bug and more about the inherent fragility of treating internal reasoning as a secure channel. The fact that models treated their own encrypted reasoning traces as sacrosanct instructions creates a dangerous new class of prompt injection, where an attacker can weaponize a model's own hidden thoughts against it or its siblings. This suggests that securing AI systems requires a paradigm beyond traditional software security, one that accounts for the semantic weight models assign to their internal processes. The industry's rapid response in patching the flaw is encouraging, but the underlying architectural risk may persist.
Researchers say they extracted hidden reasoning from major LLM APIs
A now-patched vulnerability allegedly allowed encrypted reasoning traces to be replayed and decrypted.
AIpressr commentary on an article originally published by Simon Willison.
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Editor's Take
Simon Willison highlights a research paper detailing a security flaw in the APIs of major AI providers. The reported vulnerability, which has since been patched, allowed encrypted chain-of-thought tokens to be exfiltrated and replayed. This incident underscores a critical, often overlooked attack surface in proprietary AI systems: the very mechanisms designed to obscure internal reasoning can become vectors for data leakage and novel jailbreaks.
“We take a trace produced by a frontier model, replay it into a weaker sibling, jailbreak the weaker model, and recover the stronger model’s hidden reasoning in plaintext.”
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