PHP Prepares Emergency Fixes for Two Critical Remote Code Execution Flaws

PHP will release emergency fixes for two critical RCE flaws rated 9.2, as researchers warn of potential risks to exposed and unsupported systems.

PHP is preparing an emergency security release for two critical vulnerabilities that could let attackers execute code remotely on affected servers. The update is scheduled for today, October 21 at 14:00 UTC, after details of the flaws leaked online ahead of their planned disclosure.

The PHP security team confirmed both vulnerabilities carry a CVSS v4.0 score of 9.2. It hasn’t yet published their technical details, confirmed the affected versions, or identified the releases that will fix them. The official PHP announcement says the full information will accompany the security updates.

“The PHP security team would like to give advance notice of an upcoming security release. It is scheduled for Wednesday, 21 October 2026 at 14:00 UTC. It addresses two critical vulnerabilities, both rated CVSS v4.0 9.2.” states the announcement.

“All PHP users are encouraged to prepare now so they can upgrade as soon as the release is available. We reserve the right to release earlier should details of either vulnerability become public, or should evidence of active exploitation appear in the wild. Full details, affected versions, and the fixed versions will be published with the release.”

Researchers dubbed the vulnerabilities as php2shell, using the identifiers CVE-2026-109618 and CVE-2026-109619. The identifiers and the claim that the flaws allow remote code execution come from reports outside PHP’s initial advisory, rather than from a published technical analysis by the project.

According to the Hacker News, the two critical PHP vulnerabilities would be disclosed on October 22. The post described them as remote code execution flaws with CVSS scores of 10.0 and said they affected versions dating back to PHP 5.

Researchers at watchTowr subsequently confirmed that the vulnerabilities were real and said the information had leaked before the agreed disclosure date. The company also reported that it had reproduced one of the flaws, CVE-2026-109618, but withheld technical details while patches remained unavailable.

PHP published its advance security notice later that day, setting the release for Wednesday, October 21, one day before the date reported in the leak. The team also reserved the right to release the fixes earlier if technical details became public or it found evidence of active exploitation.

The difference between the reported severity scores matters. The leaked information cited CVSS 10.0, while PHP officially rated both vulnerabilities 9.2 under CVSS version 4.0. Until the vendor publishes its technical advisory, the official score is the one administrators should use when describing PHP’s assessment.

The main concern is the possibility that the flaws affect a wide range of PHP installations. Reports have suggested that versions from PHP 5 onward could be vulnerable, but watchTowr’s FAQ explicitly notes that the scope hasn’t been confirmed by an official vendor advisory.

“The report claims the vulnerability affects every PHP version from PHP 5 onward, though this scope has not been confirmed by an official vendor advisory. No specific configuration or feature requirement has been described in the available report.” states watchTowr.

“Until PHP publishes an official advisory, security teams cannot determine which specific deployments face the greatest exposure; every organization running PHP in production should prepare to act quickly once a fix is confirmed.”

Administrators also don’t yet know which PHP components are involved or whether exploitation depends on a particular configuration or deployment mode. Those details will determine how attackers could reach the vulnerable code and which systems need the most urgent attention.

PHP’s supported versions policy adds another complication. The project currently supports four release branches, PHP 8.2 through 8.5, while older branches no longer receive security updates from the PHP project.

The anticipated fixes are PHP 8.5.12, 8.4.27, 8.3.36 and 8.2.35, according to tracking by Mallory. These version numbers were predictions ahead of the release, not confirmed package versions in PHP’s advance notice.

If the vulnerabilities affect older releases, organizations running PHP 8.1, 8.0, 7.x or 5.x may not receive an upstream fix. They may need to upgrade to a supported branch, apply any security updates provided by their operating system vendor, or restrict access to affected systems until they can remediate them.

Research by Mallory highlights the scale of the potential problem. Using Shodan data collected on October 20, the company identified about 884,000 internet-facing hosts reporting PHP 8.1 or an older version, representing roughly 59% of the 1.5 million hosts that disclosed a PHP version in their HTTP banners.

These figures don’t establish that every host is vulnerable. The count identifies systems running older PHP versions that may not receive a direct fix from the PHP project if the reported scope is confirmed. Another 740,000 hosts reported PHP without revealing a version, making it harder to assess the full exposure.

The numbers also count hosts, not individual websites or organizations. Shared hosting can place many websites on the same server, while software vendors and hosting providers may bundle PHP into products that administrators don’t recognize as PHP installations.

That makes asset discovery an important first step. Security teams should check web servers, Windows systems, vendor appliances, hosting control panels such as cPanel and Plesk, and applications that include their own PHP runtime.

PHP hasn’t published a workaround in its advance notice. Until the fixes become available, organizations should identify their PHP installations and prepare to install the correct update as soon as the vendor publishes it.

Internet-facing systems should take priority, particularly servers running business-critical applications or processing sensitive information. Administrators should also check with their Linux distribution and hosting provider, since vendors sometimes backport security fixes without changing the upstream version number in the way expected.

For installations running end-of-life PHP, the options are less comfortable. Organizations should plan an upgrade or reduce exposure by taking vulnerable services offline, restricting access through a VPN or IP allowlist, or placing them behind a web application firewall while a longer-term fix is prepared.

CERT-EU’s security advisory recommends considering the isolation of internet-facing applications from public networks when immediate patching isn’t possible.

“CERT-EU strongly recommends identifying PHP-based applications and preparing to patch as soon as fixed versions become available.”states CERT-EU. “Where immediate remediation is not feasible, organisations should consider isolating internet-facing applications from public networks until a fix can be applied.”

This is a precautionary measure, not a confirmed workaround for either PHP vulnerability.

Monitoring process activity can also help identify suspicious behavior. On Linux, security teams should investigate PHP-related processes such as php-fpm, php-cgi, httpd or apache2 launching unexpected shells, interpreters or download utilities, including sh, bash, python, curl and wget.

Florian Roth’s open-source process-watcher can log programs launched by PHP processes and record their command lines. It provides visibility into process activity, but it doesn’t block an exploit or prevent a malicious command from running.

If an investigation uncovers suspicious activity, teams should isolate the affected server, preserve PHP and web server logs, and check for newly created files in web roots, web shells, unexpected scheduled tasks, cron jobs and user accounts. Those steps can help determine whether an attacker has already gained access, rather than simply whether a server was exposed.

As of October 21, Huntress said it hadn’t observed exploitation in attacks against its partner environments and hadn’t developed or reproduced a proof of concept. watchTowr’s FAQ also listed no reported exploitation and no vendor patch at the time of its update.

That doesn’t mean administrators can safely wait to assess their exposure. Once technical details and fixes become public, attackers may be able to develop working exploits more quickly, particularly if the vulnerabilities affect widely deployed versions of PHP.

A previous PHP flaw illustrates how quickly the situation can change. When CVE-2024-4577, which affected PHP running in CGI mode on Windows, became public in June 2024, Akamai reported exploit attempts against its honeypot servers within 24 hours.

The scheduled release should answer the questions administrators still face: which versions are affected, which components contain the flaws, whether exploitation requires a particular configuration, and which updates fix each issue. Until then, the priority is straightforward: know where PHP runs, prepare the updates, and avoid leaving internet-facing systems on unsupported versions without additional protection.

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Pierluigi Paganini

(SecurityAffairs – hacking, PHP)