PHP2Shell: Mass Exploitation Looms for Leaked Critical PHP Flaws

Two critical PHP remote code execution vulnerabilities will be patched in an emergency release on October 21. Fixes are only expected for supported PHP 8.x branches. Key takeaways CVE-2026-109618 and CVE-2026-109619 are critical vulnerabilities in PHP, both rated CVSSv4.0 9.2 by the PHP security team. Public reporting describes both as remote code execution vulnerabilities. watchTowr says it believes it has reproduced CVE-2026-109618, and Cloudflare CTO Dane Knecht says the company is seeing early attacks emerging. The patch release is scheduled for October 21, 2026 at 14:00 UTC. Version numbers reported before the release point to PHP 8.5.12, 8.4.27, 8.3.36 and 8.2.35. End-of-life branches are not expected to receive fixes. Background Tenable's Research Special Operations (RSO) team has compiled this blog to answer Frequently Asked Questions (FAQ) regarding two critical vulnerabilities in PHP that were announced on October 20, 2026. FAQ When were these PHP vulnerabilities first disclosed? On October 20, 2026, the CVE identifiers circulated on Hacker News and social media. Later that day, the PHP security team published an advance notice of a security release scheduled for October 21 at 14:00 UTC (10:00 AM ET) to address two critical vulnerabilities. The notice said the team could release earlier if details became public or if exploitation appeared in the wild. CERT-EU also published an advisory (2026-018) naming both CVEs. According to watchTowr , the vulnerabilities were originally set to be disclosed on Thursday, October 22, under embargo. A video shared by researcher Kirill Firsov demonstrates the exploit chain, dubbed php2shell. Firsov credited the video and exploit to researcher LCFR and Calif.io. The PHP security team is giving advance notice: Upcoming security release Wed, Oct 21st 2026, 14:00UTC, two critical vulnerabilities, both rated CVSSv4 9.2. PHP users are encouraged to prepare to update. Earlier release if details become public or active exploit evidence. — The PHP Foundation (@ThePHPF) October 20, 2026 What are CVE-2026-109618 and CVE-2026-109619? CVE Description CVSSv4.0 CVE-2026-109618 Unspecified PHP Vulnerability 9.2 CVE-2026-109619 Unspecified PHP Vulnerability 9.2 CVE-2026-109618 and CVE-2026-109619 are critical vulnerabilities in PHP. Public reporting describes both as remote code execution vulnerabilities. The PHP security team has not published technical details before the patch release. CVSS scores differ across sources. The PHP security team rates both vulnerabilities as CVSSv4.0 9.2. Some early reports, including watchTowr and a Hacker News post, describe them as CVSS 10.0. We will update this blog once PHP publishes its advisory. Which PHP versions are affected? CERT-EU says these vulnerabilities could affect all PHP versions from PHP 5 onwards, and the demonstration video references PHP 5.4.0 and later. PHP will publish the official list of affected and fixed versions with the release. Before the release, security researcher Kevin Beaumont reported the following fixed versions: Affected Versions Fixed Version (expected) PHP 8.5.x 8.5.12 PHP 8.4.x 8.4.27 PHP 8.3.x 8.3.36 PHP 8.2.x 8.2.35 PHP 5.x through 8.1.x End-of-life, no fix expected Linux distributions that ship older PHP packages may backport fixes, so organizations using distribution packages should check their vendor's advisories. How widespread is PHP, and how many hosts are potentially affected? According to W3Techs , PHP is used by 69.3% of websites whose server-side language is known. Platforms such as WordPress, Drupal, Joomla, Laravel and Magento all run on PHP. Security researcher Silas Cutler's rough estimate is that over 1.3 million internet-exposed hosts are potentially vulnerable. A Shodan search by Henk Poley counts over 1.9 million internet-exposed hosts running PHP. Has exploitation been observed in the wild? On October 21, Cloudflare CTO Dane Knecht said the company is "seeing early attacks emerging" and is updating its miti…