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Claude Opus 5 enabled researchers to hack into OpenAI systems

evals guardrails security

Independent security researchers at startup Hacktron AI used Anthropic's Claude Opus 5 to chain two vulnerabilities and gain access to OpenAI employee ChatGPT and Codex accounts, including one linked to OpenAI's GitHub organization. The attack was conducted as part of OpenAI's bug-bounty program and netted a $6,500 award; OpenAI says it has since resolved the issues. Critically, the previous model, Claude Opus 4.8, failed to produce a working exploit across multiple sessions — but within hours of Opus 5's release, the same problem was solved, illustrating a sharp capability jump. The entry point was a memory bug in the open-source image library libheif, reachable through OpenAI's Discourse-powered community forum; the flaw had already been patched by developers but was never assigned a CVE (a standardized public vulnerability identifier), so Discourse was still running the vulnerable version.

Analysis

Showing the shorter version.

Anthropic's Claude Opus 5 helped security researchers chain together a multi-step exploit that got them into OpenAI's systems. That is the first documented case of a frontier AI model enabling an intrusion into a direct competitor's infrastructure, and it is going to be hard to un-see.

The mechanism matters. Opus 5 did not find a new vulnerability. It connected known pieces under ambiguity, reasoning across steps where each one is defensible and the combination is the attack. That is a different capability than what current red-team evals measure. The existing "cyber-offense" categories in Anthropic's and OpenAI's scaling policies test for bug-finding. Chaining is harder, subtler, and now publicly demonstrated.

Every safety team at every major lab saw this happen to a named competitor. The cheap, reputation-protecting response is to add a chaining-specific evaluation and say so in the next system card. The cost of one documented eval is low. The cost of being caught flat-footed on this twice is high.

The call: before June 2027, at least one of OpenAI, Anthropic, or Google DeepMind publishes a safety or system card that names multi-step exploit chaining as a distinct tested capability. Medium confidence. The incentive is clearly there; the only risk is timing against a specific release window.

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