Claude couldn’t hack OpenAI. Then Anthropic shipped Opus 5.

Claude couldn’t hack OpenAI. Then Anthropic shipped Opus 5. Three security researchers at Hacktron AI found a memory-corruption bug in a widely used image library. Finding it was the easy part. The hard part was turning it into something that works on a real server, so on July 24 they handed that job to Anthropic’s Claude Opus 4.8. The model managed it only with the operating system’s memory randomization switched off. With the protection on - this is the way every production box runs it - nothing it wrote held up. That evening, Anthropic released Opus 5. The researchers came back the next morning with the same bug and the new model. Roughly three hours later, Opus 5 had a working ARM64 exploit running against a Mac on their desk. About four hours after that, they had remote code execution against a test forum. Less than 72 hours after they started, they were reading from OpenAI’s private monorepo - using an OpenAI employee’s Codex account to open a pull request against a README, then stopping there. Hacktron AI published its account of the incident on its website this week. It started with an image The bug wasn’t in anything OpenAI wrote. Hacktron was testing community.openai.com , the company’s user forum, which runs on Discourse - the same off-the-shelf forum software behind thousands of other sites. Discourse normally screens uploaded images with FastImage. But FastImage doesn’t handle HEIC and HEIF, so those files get passed to ImageMagick instead, and ImageMagick decodes them with libheif . The version running in the Debian 12 base image the forum used, 1.19.7, had a heap buffer overflow that a specially crafted file could trigger. A fix had landed upstream the previous year. But the commit wasn’t documented as a security fix and never got a CVE, so it never triggered a backport into the Debian package the forum was using - a patched bug that stayed exploitable because nobody labeled it. The researchers adapted the exploit for the x86-64 and jemalloc configuration Discourse runs, and a malformed HEIC image was enough to trigger remote code execution. Discourse later confirmed the vulnerability in security advisory GHSA-vhm9-85gw-x335, rating the upstream libheif flaw - tracked as CVE-2026-32882 - 8.8 out of 10 on the CVSS severity scale. The New Stack has reached out to Hacktron AI for additional details about the researchers’ use of Claude and will update this story if we hear back. One exploit, a much larger path Code execution on a forum is a bad day for the forum. But it shouldn’t be a bad day for the company that owns the forum. This is where the chain crossed into something that was OpenAI’s own. Hacktron then found a flaw in OpenAI’s single sign-on system: sign-in tokens issued for the forum carried excessive permissions, granting full API access to the linked ChatGPT and Codex accounts. Some of those accounts belonged to OpenAI employees. One employee’s Codex account was connected to OpenAI’s GitHub environment, opening a path to the company’s private repositories. Hacktron says other accounts could have exposed connected services including Slack and email. The team stopped there. Using Codex, they made a harmless documentation change against OpenAI’s private openai/openai monorepo and opened a pull request - enough to prove the access was real, and nothing more. Hacktron’s write-up says the pull request’s details were redacted at OpenAI’s request. From assistant to exploit developer Up to this point, those three experienced researchers were still in the loop. So Hacktron ran the experiment again with the humans mostly out of it. They put Claude in an autonomous agent loop - giving it a goal, a target, and time to keep working - pointed at a Discourse instance of their own. The model got there on its own, achieving remote code execution and demonstrating it by reading /etc/hosts from inside the container. Getting it started took one piece of misdirection: Opus refused to write an exploit aimed at a live remote host. So the team proxied their own instance through rce.ee/ctf-forum , a URL that made the target look like it was part of a capture-the-flag exercise. Memory-corruption exploitation has always been specialist work, invovling memory layouts, allocators, operating system internals, and protections to make all of it wildly unreliable. Hacktron’s run signals a meaningful share of that work might be able to be delegated to AI now. It also suggests the line between security research and attack development is - from the model’s side, anyway - partly a question of what you consider a target. The full chain Put together, the attack looked like this: HEIF upload → libheif overflow → code execution on the forum → over-permissioned SSO tokens → employee ChatGPT/Codex account → connected GitHub → pull request in openai/openai A two-month project, under $3,000 The OpenAI intrusion was one thread in a broader project the team called “HEIF Heist,” a roughly two-month sweep of image-processing infrastructure across multiple major technology platforms. The whole effort consumed less than $3,000 in model tokens. OpenAI paid Hacktron a $6,500 bounty for the account-takeover flaw on its side. It has since narrowed the permissions on community sign-in tokens and revoked the affected tokens and sessions.