Team using Anthropic's Claude hacked into OpenAI's internal code repository. Claude Opus 5 exploited a bug in libheif, an image library used by Discourse, OpenAI's forum host. The stolen login tokens also worked on ChatGPT, including employees' accounts. Reward: a $6,500 bug bounty. Heap buffer overflow that could be turned into remote code execution. https://www.wsj.com/tech/ai/hackers-used-anthropics-claude-to-break-into-openai-b40ba883