The project overseeing the programming language is releasing patches Wednesday, with the internet racing to patch the 9.2 rated flaw.
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The PHP project released patches Wednesday for two critical vulnerabilities in a programming language used in an extremely large portion of the internet.
The patch addresses two flaws, catalogued as CVE-2026-109618 and CVE-2026-109619, both rated 9.2 on the CVSS v4.0 severity scale, which tops out at 10. Researchers describe them as remote code execution vulnerabilities, which could let an attacker run their own code on a server and potentially take control of it.
The vulnerabilities have been dubbed “php2shell” by researchers. While the industry has spent the past 24 hours sounding the alarm over the vulnerabilities, there has been very little in terms of reported exploitation as of Wednesday afternoon.
In a release, the Cybersecurity and Infrastructure Security Agency said it wasn’t aware of any exploitation.
“While CISA has not observed exploitation of these vulnerabilities as of the time of publication, they pose a risk to organizations if left unpatched,” the release reads.
Multiple researchers have told CyberScoop that they have observed very little activity outside of reconnaissance that is probing to see what vulnerable systems are still connected to the internet.
“We see clear evidence attackers are actively probing and performing reconnaissance across PHP applications,” Kelly Shortridge, chief product officer at Fastly, told CyberScoop. “The gap between disclosure and widespread, repeatable exploitation is typically hours to a few days for vulnerabilities of this severity and attack ROI.”
Neither the technical cause nor a complete list of affected versions has been officially confirmed, with the PHP team saying full details will be published with the release. An advisory from CERT-EU, the European Union’s computer emergency response team, says the flaws could affect every version of PHP from 5 onward.
The security firm watchTowr said Tuesday the vulnerabilities had been set for release Thursday under embargo. The PHP team moved the release up a day and said it could act sooner still if details became public or exploitation appeared.
A video demonstrating an exploit chain spread online overnight via researcher Kirill Firsov, who shared it and credited researchers known as LCFR and Calif.io. watchTowr said it had reproduced one of the flaws. Code claiming to exploit the flaws is circulating but has not been verified, and security firms caution such code is sometimes laced with malware.
Dane Knecht, chief technology officer at Cloudflare, said Wednesday the company was “seeing early attacks emerging” and updating its defenses as new vectors appeared. Cloudflare deployed firewall rules covering known exploit vectors to all customers, including free accounts, while calling the protection “a stopgap.”
The potential exposure is broad. PHP runs between 70-80% of websites whose server-side language is known, according to market research, and underpins platforms including WordPress, Drupal, Joomla and Laravel. Researchers estimated more than 1.3 million internet-exposed hosts could be vulnerable, and a Shodan search counted about 1.9 million. Among servers that disclose their version, most run branches are no longer receiving security updates: about 758,000 run versions from 5.4 through 8.1, compared with 272,000 on supported branches, according to VirusTotal.
CERT-EU and Britain’s National Cyber Security Centre advised organizations to prepare to update systems quickly and suggested isolating internet-facing applications where immediate patching was not feasible. PHP flaws have been exploited before: the U.S. Cybersecurity and Infrastructure Security Agency’s known-exploited vulnerability catalog lists three in PHP itself, two used in ransomware campaigns.
The vulnerability was discovered by AI cybersecurity firm Calif, using OpenAI’s cybersecurity-focused AI model GPT-5.6 Sol. Wiz, an AI security firm purchased by Google in March, also independently discovered and reported the flaw, according to a blog posted by OpenAI on Wednesday.
The discovery sparked a two-month collaborative effort between OpenAI, PHP maintainers, researchers and security providers to develop a long-term technical fix and prepare for public disclosure.
OpenAI said the priority for all organizations relying on PHP is to apply the new patches, and offered a free tool and other support to help identify vulnerable versions.
“To our knowledge, frontier AI found these vulnerabilities before attackers did, opening a Defender’s Window for maintainers and security providers to prepare fixes and protections ahead of disclosure,” OpenAI wrote in an unsigned blog.
OpenAI also said the PHP flaw is among “several significant vulnerabilities we’ve already found and are working to fix, and we expect similar findings to increase sharply in the coming months.”
In a blog posted the same day, researchers at Wiz said they had discovered “multiple critical vulnerabilities” in PHP, all related to memory safety using GPT-5.6 Sol, their own Wiz Atlas AI tool and Google’s Gemini 4 Argon to conduct their research.
Perhaps most concerning: The bug existed for decades prior to the emergence of modern AI tools, but it’s so complex and technically arduous that few attackers were likely capable of exploiting it.
According to Wiz, it required developing exploits for “notoriously complex” memory bugs that work across different PHP versions, configurations and application behaviors. It would also have to account for differences in PHP deployments that could render the exploit harmless, and each change would require more testing, analysis and debugging.
In the era of AI hacking, “this is no longer a barrier,” the Wiz researchers said.
Large language models can adapt exploits to different PHP versions, configurations or memory layouts, use third-party testing and debugging tools, and carry out a series of other functions for “reducing the specialist effort required for each target.”
“This changes the economics of both discovery and exploitation,” wrote Wiz researchers Sagi Tzadik, Shir Tamari, Nir Ohfeld and Tomer Schwartz. “As AI reduces the effort needed to develop and adapt complex exploits, vulnerabilities that once seemed impractical to exploit become viable targets.”
More information is expected over the course of the day. The PHP team is to publish the full advisory with the release, and security firms including Huntress and Tenable said they would update their analyses as technical details and proof-of-concept code emerge.
UPDATE: 10/21/2026, 3:00 p.m. ET: This article was updated to include infromation from CISA and from industry researchers.
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