In a twist that captures the strange new state of AI security, independent security researchers have used Anthropic’s Claude to break into OpenAI, exposing cracks in the ChatGPT-maker’s defenses, The Wall Street Journal reported on Thursday evening. A three-person security team at startup Hacktron AI carried out the attack as part of an OpenAI bug-bounty program. Hacktron reported its findings to OpenAI, which gave the startup a $6,500 award.
The team managed to chain together two critical vulnerabilities to gain access to multiple OpenAI employee ChatGPT accounts, which gave them entry into the company’s software. OpenAI says it has resolved the issues Hacktron uncovered, which happens to come at a moment when top AI companies are under growing pressure over safety. This incident comes several weeks after OpenAI’s own AI agents broke containment during a cybersecurity evaluation and hacked Hugging Face, demonstrating just how capable AI models are getting at making their own decisions.
It also highlights how off-the-shelf technology can be used to find vulnerabilities in even the most advanced companies’ infrastructure. According to a blog the researchers published, the entry point was a mundane image upload. When users posted HEIF or HEIC image files (the format iPhones use by default) to OpenAI’s community forum, Discourse passed them through a chain of behind-the-scenes tools to convert them into standard JPEGs.
Its first stop was ImageMagick, a decades-old, open source utility used to resize images. Because ImageMagick’s usual toolkit can’t deal with Apple’s format, it handed the file off to another library called libheif to do the decoding. Buried inside libheif was a memory bug that exposed a path for an attacker to sneak in their own instructions.
In this case, feeding the library a specially crafted image caused it to miscalculate where one image was positioned on top of another, which proved enough to hijack the server. What may be uncomfortable for the cybersecurity community is that bug had already been fixed months earlier by libheif’s developers. But the fix was never formally flagged as a vulnerability, meaning it never got a CVE (common vulnerabilities and exposures) number, the industry’s standard way to track known security weaknesses.
Hacktron says that may explain why the software used by Discourse was still running the vulnerable version. Notably, the researchers said the Claude model they were using — a special version of Opus 4.8 made available for cybersecurity researchers — couldn’t build a working exploit at first. That changed overnight, when Anthropic released Opus 5.
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