A heap overflow and SSO misconfiguration to compromise OpenAI internal repos

Intro

On July 25, 2026, we chained two critical vulnerabilities to compromise multiple OpenAI employees’ ChatGPT accounts. With these accounts, we could then access internal OpenAI repositories, and potentially many other connectors.

To prove we had in fact gained the access we believed without allowing ourselves to learn any sensitive information, we used the employee’s Codex to open a PR #1186742 in OpenAI’s internal monorepo openai/openai.

1. libheifImage decoder
2. DebianMissing security backport
3. ImageMagickUses libheif
4. DiscourseImage uploads
5. OpenAI forumcommunity.openai.com
6. OpenAI SSO Identity flaw
7. ChatGPT / CodexAccount access
8. GitHubConnected integration
9. Internal reposOpenAI

Until two months ago, any user or OpenAI employee logging into OpenAI’s own help forum (community.openai.com) could have had their ChatGPT and Codex accounts taken over. Since people can connect various services to Codex and ChatGPT, the scope of what we could theoretically access was huge, including GitHub, Slack and emails.

The entire timeline from initial discovery to access to OpenAI repo access took place in less than 72 hours.

We immediately reported the initial vulnerability to OpenAI and Discourse and worked with them to coordinate the patch. We appreciate their attention to detail and fast resolution of this issue. OpenAI also paid us a $6,500 bounty.

We provide a full timeline of the disclosure process here. The rest of the post details how we discovered the two vulnerabilities, how we used claude models, as well as our takeaways from this experience.

Background

A few months ago, our team at Hacktron, led by Harsh Jaiswal alongside Mohan Pedhapati and Rahul Maini, began researching frontier AI companies to find security vulnerabilities. This led us to discover an SSO misconfiguration in OpenAI’s identity infrastructure and a libheif RCE in the community forum used by OpenAI.

We’ve since expanded the research into HEIF Heist, a multi-month investigation tracing libheif across Slack, Meta, GitHub Enterprise, Ruby on Rails, and Node.js frameworks such as Next.js, Astro, and Gatsby. A surprising amount of widely-used software depends on this one image-processing library.

If your application processes user-controlled images and accepts .heic/.heif/.avif images, it is highly likely it is affected. Please reach out to us at [email protected] if you need any kind of assistance.

Warning

Patch notice: If you self-host Discourse, rebuild your installation now. Older Docker images may contain a vulnerable libheif dependency that permits code execution through an image upload. Run git pull followed by ./launcher rebuild app from /var/discourse; a web-interface update alone may not replace the underlying image. Discourse-hosted customers have already been patched. See the security advisory.

OpenAI uses Discourse for their forum and allows “Sign in with OpenAI” through auth.openai.com. After getting a good understanding of OpenAI’s services and infrastructure, we had reason to believe that compromising the forum could create a path into broader OpenAI services through this identity flow. To test that hypothesis, we first needed remote code execution on an OpenAI service like the Discourse community forum.

While the Discourse app itself is actually not an easy target (we have looked into it in the past), we thought we could go after a dependency.

Heap buffer overflow in libheif

On July 23, we started reviewing Discourse’s image-upload pipeline, and we found that HEIC and HEIF files followed an unusual path. Discourse normally used FastImage for image checks, but because FastImage did not support HEIF, it passed those files to ImageMagick’s magick command for conversion.² That exposed the underlying libheif parser directly to attacker-controlled files.

We started an Opus 4.8 session with the Discourse Docker image and asked it to inspect the installed libheif package for security issues. After a while, it found that some particular security fixes were not back-ported to the libheif package. This allowed an heap buffer overflow leading to OOB R/W primitives during HEIC decoding.

Interestingly, the vulnerable code had been changed upstream the previous year, but the commit was not documented as a security fix and received no CVE.³ This might be a reason why Debian 12 and 13 have not received the security relevant backports in time. Because Discourse’s Docker image was based on Debian 12, it installed the vulnerable libheif version 1.19.7. Even Debian 13 still shipped the vulnerable version 1.19.8 at the time. Since then, Debian has published its security update for Debian 13 on August 8, 2026. ⁴

On July 24, we used Opus 4.8 to develop a working ImageMagick/libheif code-execution exploit with ASLR disabled. We then launched several separate sessions to make it reliable against Discourse’s default configuration with ASLR enabled, which wasn’t fruitful.

Opus 5 Released

That evening, Anthropic released Claude Opus 5.⁵We started a new session, which first produced a working ARM64 exploit for a local Mac within 3 hours. We then asked it to port the exploit to the x86-64 environment and jemalloc configuration used by Discourse.

By 6:00 a.m. on July 25, we had confirmed local RCE through an image upload. We then placed Claude in an autonomous /goal loop against our own Discourse Cloud instance, proxied through rce.ee/ctf-forum to make it look like a CTF target as Opus refused write exploit for remote instances.

When we checked again at 10:00 a.m., the agent had achieved RCE on Discourse Cloud and demonstrated access by reading /etc/hosts. Using the generated exploit script, we managed to get RCE on OpenAI’s instance.

After we had confirmed our hypothesis of no interaction account takeover of ChatGPT/Codex accounts from active members of the forum, we immediately sent our report to OpenAI. We then took over an OpenAI employee’s account, whose Codex was connected to OpenAI’s Github organization. To demonstrate impact without actually accessing any internal code, we sent a prompt to this employee’s Codex account to open a PR for us in OpenAI’s internal monorepo. Then we stopped any further testing.

We updated the BugCrowd submission with the impact proof and alerted OpenAI security. We also prepared a report for Discourse and reported it to their HackerOne program. Discourse received the report on a Saturday, replied on Sunday, and had a fix by Monday (kudos for speed). They also immediately started sandboxing ImageMagick.

We want to emphasize that the vulnerability to escalate is not Discourse-specific. It is an OpenAI SSO issue that turned the forum compromise into access to ChatGPT and Codex. If any first-party or third-party OpenAI service using the OpenAI SSO was compromised, it would lead to same access - Discourse was merely one way of proofing it.

Costs of finding these vulnerabilities

The Discourse and OpenAI hack took a few days for an agent, and just a few hours of human time. The whole HEIF Heist research project going after Slack, Zoom, Meta, adn more took two-months, cost less than $3,000 in tokens in total, and was conducted by three researchers. Adapting the exploit to each new company usually took only one or two days.

We observed that every new model is getting increasingly capable, as evident by the Discourse exploit presented in this report. Opus 4.8 struggled across several sessions to produce a working exploit with ASLR enabled. Within hours of Opus 5’s release, we gave it the same problem and it succeeded. Across the broader campaign, we saw another clear jump from Opus 5 to GPT-5.6 Sol, when we had to exploit the vulnerability without knowing anything about the target system besides that it’s vulnerable.

For each target, testing began with an image upload. From there, we turned memory corruption into a reliable memory leak or shell, usually without knowing the exact libheif version, libc version, or deployment environment. The AI started almost blind and adapted the exploit for each company within one or two days. We are not aware of any company that detected the activity except Shopify, even after thousands of images were sent and their image processors repeatedly crashed.

When code execution landed inside a sandbox or restricted environment, the models also helped with privilege escalation, lateral movement, and bypassing existing defenses. This was not completly autonomous hacking, and skilled human guidance remained important, but the amount of work a small team could perform increased dramatically.

Epilogue

Software has long benefited from a kind of security through complexity. The code and even the vulnerability could be public, but turning a bug into a reliable exploit still required rare expertise, significant time, and knowledge of the target environment. Known memory corruption vulnerabilities were expensive to operationalize, while zero-days were mostly reserved for the highest-value targets.

This was never a real security boundary, but it protected ordinary companies in practice from software vulnerabilities. AI is removing that protection by turning more of this scarce expertise into compute. Work that once required a well-resourced team and months of effort can now be compressed into days.

Security assumptions must catch up with attacker capabilities. A realistic threat model should take into account the economics of exploitation today, instead of relying on outdated assumptions ⁶ about who can carry out sophisticated attacks.

Hacktron’s mission is to help secure the internet by finding and eliminating vulnerabilities in widely trusted software before malicious actors do. We are continuing this research across frontier labs and other internet-critical systems. If you are responsible for securing one of them, we would like to work with you.

Versions affected and patches

HEIF Heist is not tied to a single version. It targets an entire ecosystem of vulnerabilities across multiple release families (e.g. 1.19.x, 1.20.x, 1.22.x, 1.23.x). Any deployment lacking the latest upstream security patches is potentially vulnerable.

• Update upstream. Install the latest security-patched libheif and libde265 packages through your distribution’s security channel or an upstream release. As of September 14, 2026, the latest upstream libheif security release is v1.23.4; v1.23.2 has been superseded by further security fixes. Distribution packages may carry backported fixes under an older upstream version number, so check the package security advisory as well.^7 4
• Defense in depth. Given the complexity of the ISO base media file format and the pace of decoder updates, future memory-safety flaws are likely. Production architectures should disable untrusted HEIF/AVIF decoding where it is not needed, or isolate image-processing pipelines inside hardened, ephemeral sandboxes. ImageMagick’s security policy supports restricting accepted formats and resource usage. ⁸

Acknowledgements

We thank Sudanshu Rajhbhar for technical assistance, and Zayne Zhang, Fabian Faessler, Robert Chen, and Jessica Ruan for proofreading, reviewing drafts, and providing feedback that improved this post.

References

Work with the team behind this research.

Hacktron brings together top CTF researchers, experienced red teamers, and offensive security researchers. We use AI to accelerate security research, finding and eliminating vulnerabilities in widely trusted software before malicious actors do. We’re continuing our research across frontier labs and other internet-critical systems. If you’re responsible for securing one of them, we’d like to work with you.

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