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The vulnerabilities designated as CVE-2026-109618 and CVE-2026-109619, collectively known as “PHP2Shell”, represent critical remote code execution flaws located directly within the PHP core engine rather than in third-party applications.
These vulnerabilities affect both mod_php and PHP-FPM deployment architectures across all active versions from 5.4 up to recent releases.
The attack mechanism specifically targets PHP’s session upload-progress feature, which processes incoming multipart/form-data requests before any application-level code or framework routing is executed.
When an attacker sends a specially crafted multipart HTTP request containing malicious payload structures, the PHP interpreter parses the form data and interacts with the session upload-progress handler.
CVE-2026-109619 involves a fatal-error backtrace use-after-free condition paired with OPcache type confusion during the handling of exceptional states in the request heap.
When a fatal error occurs and frees the request heap memory, the upload-progress handler improperly handles references, allowing freed worker memory to be exposed or manipulated.
Concurrently, CVE-2026-109618 facilitates a memory disclosure vector resembling historical information leakage flaws, returning sensitive heap data inside PHPSESSID response cookies.
An unauthenticated attacker can chain these two distinct flaws into a single pre-authentication remote code execution attack vector against exposed web servers.
Because the vulnerable parsing routine executes at the engine level prior to authentication or application logic checks, standard application maintenance modes or routing firewalls are bypassed entirely.
Applications such as Magento, WordPress, and custom PHP platforms running on unpatched runtimes are fully exposed to complete system compromise.
Attackers leveraging this chain can spawn interactive shell processes, execute arbitrary system binaries, and establish persistent access without valid credentials.
Early telemetry indicates active scanning and exploitation attempts targeting internet-facing PHP endpoints immediately following the vulnerability disclosures.
To thoroughly examine and verify system exposure to these flaws, specialized tooling such as verification scripts and audit utilities have been published in security repositories.
Administrators must carefully review runtime configurations, monitor worker process execution behaviors, and verify package versions to ensure complete mitigation.
DailyCVE Form:
Platform: PHP Core
Version: 5.x through 8.5
Vulnerability: Remote Code Execution
Severity: Critical
date: October 21 2026
Prediction: October 21 2026
What Undercode Say:
if ($http_content_type ~ "multipart/form-data") {
return 403;
}
nginx -t && systemctl reload nginx
ps aux | grep php-fpm
Exploit: (Educational Purposes!)
curl -X POST -F "PHP_SESSION_UPLOAD_PROGRESS=1" -F "[email protected]" http://target-server/index.php
An unauthenticated actor constructs a multipart request targeting the session upload-progress parser to trigger the use-after-free condition and execute arbitrary system commands via the spawned worker process.
Protection:
Upgrade the PHP runtime immediately to the official patched versions (such as PHP 8.5.12, 8.4.27, 8.3.36, or 8.2.35).
Temporarily block all multipart/form-data requests at the web server level using Nginx or Apache rule overrides if immediate patching is not feasible.
Deploy web application firewall rules and Cloudflare proxy configurations to filter malicious payloads before they reach the backend interpreter.
Monitor PHP worker processes closely for anomalous subprocess spawning such as interactive shells, scripting interpreters, or network utility downloads.
Impact:
Complete unauthenticated remote code execution on vulnerable web servers running unpatched PHP engines.
Full system compromise allowing attackers to read sensitive files, modify application code, deploy persistent webshells, and pivot across internal network infrastructure.
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Sources:
Reported By: github.com
Extra Source Hub:
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