AI uncovered major PHP flaws affecting 70% of websites

A major cybersecurity initiative using AI found critical flaws in PHP, a programming language used by 70% of websites. PHP, which runs on an estimated 70% of the internet, had known issues since 2024, but it took AI-assisted researchers only two weeks to turn a two-year-old bug into working exploits. OpenAI, in collaboration with a cybersecurity firm and PHP maintainers, worked to patch the flaws, releasing updated versions of PHP in October 2026. The vulnerabilities, rated at a critical severity score of 9.2, involve how PHP manages memory and handles errors, and they allow attackers to execute malicious code on affected servers, potentially taking control of websites.

The PHP Foundation has released patched versions PHP 8.2.35, 8.3.36, 8.4.27, and 8.5.12 to fix the vulnerabilities. PHP 8.1 and older versions will not receive official fixes. The coordinated release was brought forward to October 21, 2026, following premature disclosures on October 20, 2026, which led to public outcry. The two vulnerabilities, tracked as CVE-2026-109618 and CVE-2026-109619, involve flaws in how PHP manages computer memory and handles errors. The first occurs when PHP runs out of allocated memory while processing a request, potentially leaving behind incomplete internal data that the engine may later mistakenly treat as valid. The second involves a related problem in which a fatal error leaves PHP pointing to memory that has already been freed, allowing subsequent requests to access or corrupt it. Under certain conditions, attackers can exploit these weaknesses remotely, without needing login credentials, to execute malicious code on affected servers, potentially taking control of websites.

Using AI, the researchers also demonstrated that the flaws could expose sensitive information stored in server memory, including passwords, authentication tokens, and API keys. Most concerning, the vulnerabilities exist in PHP's core engine, meaning websites can be affected even if their application code has no security flaws. Both vulnerabilities received a critical severity score of 9.2 out of 10. OpenAI says human developers and security teams examined the underlying code but couldn't fully resolve the flaws, allowing them to persist for two years after discovery. Meanwhile, AI-wielding researchers demonstrated practical ways to exploit it within two weeks. Conversely, one could argue that the flaws would never have been exploitable without AI, making them effectively harmless.

OpenAI is challenging this view with its Defender's Window concept. The company argues that powerful, revolutionary technology will inevitably be used by bad actors. It therefore maintains that it is a collective responsibility to act proactively to address any potential exploitable flaws. Anthropic's Claude Mythos recently identified 'thousands of zero-day vulnerabilities' in 'every major operating system and every major web browser.’