Researchers used Claude to hack OpenAI

1. Executive summary

Security researchers at Hacktron (Harsh Jaiswal, Mohan Pedhapati, Rahul Maini) chained two vulnerabilities to reach OpenAI's internal GitHub repositories: a memory-corruption flaw in the libheif library, exploitable through the image-upload feature of Discourse forum software, followed by a flaw in OpenAI's single sign-on (SSO) system that exposed the ChatGPT and Codex sessions of anyone logged in to OpenAI's community forum, including OpenAI employees. The full chain, from initial image-processing flaw to an internal repository, took under 72 hours, and the researchers used Anthropic's Claude models to find the libheif issue and build the working exploit. OpenAI fixed its side of the chain roughly 14 hours after the initial report and paid a $6,500 bounty; no verified reference data was resolved for this item, so no CVE identifiers, CVSS scores, or CISA-KEV states can be stated. The direct risk to EMEA financial services is low (this was authorised research, not a criminal campaign), but the same chain pattern, an exploitable image-processing library in an internet-facing community platform feeding into an SSO trust path, applies to any institution running customer forums, support portals, or SSO integrations of that kind.

2. Regulatory framing

No specific DORA/NIS2 article is directly engaged by this item. The item is a coordinated, authorised security research exercise against a third party (OpenAI), not an incident at a client institution, and no fact in it triggers an incident-management, reporting, or third-party-risk obligation under the articles in scope. Institutions that operate Discourse forums or similar SSO-linked community platforms should treat §4 as ordinary vulnerability-management hygiene rather than a regulatory response.

3. Technical analysis & attack chain

The attack chain as reported by Malwarebytes, drawing on Hacktron's mid-September write-up:

1. Reconnaissance target: companies developing frontier AI models. Hacktron began looking for flaws at these companies a few months before the September write-up.
2. Vulnerability discovery in libheif. The Discourse image-upload feature processes user-uploaded images through libheif, a low-level image library. A specially crafted image triggers a flaw in the library that gives the attacker control of the Discourse server. Claude Opus 4.8 identified the issue in libheif but could not build a reliable exploit against the default Discourse configuration; after Anthropic released Claude Opus 5, the researchers produced a working exploit overnight.
3. Compromise of OpenAI's Discourse server. The researchers first validated the exploit against a test forum server, which the Claude agent took over within four hours, then ran it against OpenAI's production forum.
4. SSO flaw exploitation. The second vulnerability was in OpenAI's SSO system. It gave the researchers access to the ChatGPT and Codex accounts of users who had logged in to the Discourse forum, a population that included both public users and OpenAI employees.
5. Employee account access and lateral movement into GitHub. One compromised employee's Codex account was connected to OpenAI's GitHub organisation, which extended access to OpenAI's internal software repositories.
6. Proof of compromise. The researchers instructed the employee's Codex account to create a harmless pull request in an internal OpenAI repository. They deliberately avoided viewing sensitive information.
7. Remediation and bounty. OpenAI fixed its part of the problem approximately 14 hours after the initial report and later paid $6,500 for the OpenAI-side flaw.

Two aspects of the tradecraft matter beyond the specific target:

• AI-assisted exploit development. The capability gap between Claude Opus 4.8 (failed across several sessions to weaponise the libheif flaw against default Discourse) and Opus 5 (working exploit overnight) is the single most operationally significant fact in the item. It indicates that reliable exploit development for memory-corruption class bugs in widely deployed software is now reachable by a small team with commodity AI access and under $3,000 in token spend across a two-month project.
• Safety-control bypass. Claude refused to write an exploit for a remote system on ethical grounds. The researchers reframed the task as a capture-the-flag exercise, after which the agent compromised the test server in four hours. Prompt-level reframing defeated the refusal; the control was not a technical boundary.

Confidence caveats. Every technical claim above is single-sourced: it rests on one vendor news article (Malwarebytes) reporting Hacktron's own write-up, and no primary technical report, CVE record, or vendor advisory was available to this assessment. No CVE identifiers, CVSS scores, CISA-KEV states, or CWE classifications exist in the verified reference data for this item, and none should be inferred from the source text. The related HEIF Heist project reportedly affected services from Slack, Meta, and GitHub, with per-target exploit adaptation taking one to two days on average; this is likewise single-sourced and unverified. Attribution is not in question (the researchers published their own work), but the technical detail is uncorroborated.

4. Mitigation & containment

This was authorised research against OpenAI, so there is no active threat to contain. The controls below address the chain pattern in your own environment.

P1, within 24 hours

• Inventory every internet-facing instance of Discourse (or any other platform that processes user-uploaded images through libheif) and confirm the libheif version in use. If you cannot determine the version, treat the instance as unpatched until proven otherwise. The source gives no patched version number or CVE, so verification must come from your own package audit, not from a vendor bulletin cited here.
• Audit the trust relationship between your community or support forum and your SSO infrastructure. The OpenAI chain worked because forum compromise converted into SSO session access for ChatGPT and Codex. Map which internal systems and third-party integrations (GitHub organisations, code assistants, SaaS consoles) a forum-authenticated session can reach.

P2, within 72 hours

• Restrict what SSO federation can reach from community or support platforms. Where employees authenticate to a public-facing forum with corporate identities, ensure that forum-side compromise cannot mint or hijack sessions into developer tooling. The specific failure here was an employee Codex account linked to the corporate GitHub organisation; check whether your own developer AI tooling has equivalent standing access to source repositories.
• Review whether AI coding agents connected to your GitHub organisations can create pull requests in internal repositories without additional authorisation. Hacktron's proof of compromise was exactly that action, executed through a hijacked agent session.
• If you run image-processing pipelines on user uploads (forums, ticketing, chat), confirm that processing occurs in an isolated sandbox rather than in the web application's process. The libheif flaw gave server control from a single crafted image.

P3, within 7 days

• Update libheif and Discourse to current versions across all instances, and pin the dependency so it cannot silently regress. No specific fixed version is stated in the source material.
• Add crafted-image upload testing to your vulnerability management cycle for any platform accepting user images. The HEIF Heist project reportedly adapted the same exploit to new targets in one to two days, which sets the adaptation timeline you should assume for copycat activity.
• If your organisation permits AI-assisted security testing, note that the researchers bypassed a model's safety refusal by reframing the request as a capture-the-flag exercise. Any policy relying on model refusals as a control should be treated as administrative, not technical.

5. Indicators of compromise

No indicators of compromise available in the source material.

The sources describe one observable behaviour relevant to detection, at the target organisation only:

6. Detection

Insufficient indicators to author detection rules.

The source material contains no strings, file paths, command lines, registry keys, mutexes, or hashes belonging to the exploit or the crafted image. Product names (Discourse, libheif, Codex, Claude) and the project name (HEIF Heist) are not threat artefacts and cannot be used as detection strings.

7. Sources

• Malwarebytes, "Researchers used Claude to hack OpenAI", https://www.malwarebytes.com/blog/news/2026/09/researchers-used-claude-to-hack-openai, 2026-09-22

8. Adverse Trace position

We assess the direct client impact of this item as low: it was authorised research, responsibly disclosed, and remediated by OpenAI within roughly 14 hours of the initial report. The strategic significance is higher than the tactical detail suggests. A three-person team spent under $3,000 in AI tokens over two months and produced a reliable memory-corruption exploit against default-configured, widely deployed software, then chained it through an SSO flaw into a frontier AI company's internal source repositories; the previous model generation could not complete the exploit and the new one did it overnight, which is a measurable capability step, not vendor marketing. We assess that the chain pattern, exploitable image-processing library in an internet-facing community platform feeding an SSO trust path into developer tooling and source control, is directly transferable to financial services institutions that operate customer forums, support portals, or SSO-linked collaboration platforms, and we assess that the absence of CVE identifiers or vendor advisories in the verified reference data means clients cannot rely on CVE-driven patch processes to catch the libheif issue; dependency-level auditing is required. All technical claims in this advisory are single-sourced through the Malwarebytes report of Hacktron's write-up, and we will re-issue with updated confidence if the primary technical report, CVE records, or vendor advisories become available. Our next step is to monitor for the HEIF Heist disclosures affecting Slack, Meta, and GitHub and to assess whether any client-visible dependency chains pull in the affected libheif code paths.

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Published via PulseTrace — Adverse Trace threat intelligence.