In this post I’ll show you how I found a zeroday vulnerability in the Linux kernel using OpenAI’s o3 model. I found the vulnerability with nothing more complicated than the o3 API – no scaffolding, no agentic frameworks, no tool use.
Recently I’ve been auditing ksmbd for vulnerabilities. ksmbd is “a linux kernel server which implements SMB3 protocol in kernel space for sharing files over network.“. I started this project specifically to take a break from LLM-related tool development but after the release of o3 I couldn’t resist using the bugs I had found in ksmbd as a quick benchmark of o3’s capabilities. In a future post I’ll discuss o3’s performance across all of those bugs, but here we’ll focus on how o3 found a zeroday vulnerability during my benchmarking. The vulnerability it found is CVE-2025-37899 (fix here), a use-after-free in the handler for the SMB ‘logoff’ command. Understanding the vulnerability requires reasoning about concurrent connections to the server, and how they may share various objects in specific circumstances. o3 was able to comprehend this and spot a location where a particular object that is not referenced counted is freed while still being accessible by another thread. As far as I’m aware, this is the first public discussion of a vulnerability of that nature being found by a LLM.
Before I get into the technical details, the main takeaway from this post is this: with o3 LLMs have made a leap forward in their ability to reason about code, and if you work in vulnerability research you should start paying close attention. If you’re an expert-level vulnerability researcher or exploit developer the machines aren’t about to replace you. In fact, it is quite the opposite: they are now at a stage where they can make you significantly more efficient and effective. If you have a problem that can be represented in fewer than 10k lines of code there is a reasonable chance o3 can either solve it, or help you solve it.
Benchmarking o3 using CVE-2025-37778
Lets first discuss CVE-2025-37778, a vulnerability that I found manually and which I was using as a benchmark for o3’s capabilities when it found the zeroday, CVE-2025-37899.
CVE-2025-37778 is a use-after-free vulnerability. The issue occurs during the Kerberos authentication path when handling a “session setup” request from a remote client. To save us referring to CVE numbers, I will refer to this vulnerability as the “kerberos authentication vulnerability“.
The European Vulnerability Database (EUVD) is now fully operational, offering a streamlined platform to monitor critical and actively exploited security flaws amid the US struggles with budget cuts, delayed disclosures, and confusion around the future of its own tracking systems.
As of Tuesday, the full-fledged version of the website is up and running.
"The EU is now equipped with an essential tool designed to substantially improve the management of vulnerabilities and the risks associated with it," ENISA Executive Director Juhan Lepassaar said in a statement announcing the EUVD.
"The database ensures transparency to all users of the affected ICT products and services and will stand as an efficient source of information to find mitigation measures," Lepassaar continued.
The European Union Agency for Cybersecurity (ENISA) first announced the project in June 2024 under a mandate from the EU's Network and Information Security 2 Directive, and quietly rolled out a limited-access beta version last month during a period of uncertainty surrounding the United States' Common Vulnerabilities and Exposures (CVE) program.
Register readers — especially those tasked with vulnerability management — will recall that the US government's funding for the CVE program was set to expire in April until the US Cybersecurity and Infrastructure Security Agency, aka CISA, swooped in at the 11th hour and renewed the contract with MITRE to operate the initiative.
In Q1 2025, VulnCheck identified evidence of 159 CVEs publicly disclosed for the first time as exploited in the wild.
In Q1 2025, VulnCheck identified evidence of 159 CVEs publicly disclosed for the first time as exploited in the wild. The disclosure of known exploited vulnerabilities was from 50 different sources. We continue to see vulnerabilities being exploited at a fast pace with 28.3% of vulnerabilities being exploited within 1-day of their CVE disclosure. This trend continues from a similar pace we saw in 2024. This demonstrates the need for defenders to move fast on emerging threats while continuing to burn down their vulnerability debt.
Here are the key take-aways from our analysis and coverage of known exploited vulnerabilities:
A critical resource that cybersecurity professionals worldwide rely on to identify, mitigate and fix security vulnerabilities in software and hardware is in danger of breaking down. The federally funded, non-profit research and development organization MITRE warned today that its contract…
MITRE Vice President Yosry Barsoum has warned that U.S. government funding for the Common Vulnerabilities and Exposures (CVE) and Common Weakness Enumeration (CWE) programs expires today, which could lead to widespread disruption across the global cybersecurity industry.
NIST announced on Wednesday that it will be receiving outside help to get the National Vulnerability Database (NVD) back on track within the next few months.
The organization informed the cybersecurity community in February that it should expect delays in the analysis of Common Vulnerabilities and Exposures (CVE) identifiers in the NVD, saying that it was working to establish a consortium to improve the program.
Anchore engineers are investigating why as of February 15, 2024, NIST has almost completely stopped updating NVD with analysis for CVE IDs.
