Microsoft Details Cookie-Controlled PHP Web Shells Persisting via Cron on Linux Servers
Microsoft Details Cookie-Controlled PHP Web Shells Persisting via Cron on Linux Servers
https://thehackernews.com/2026/04/microsoft-details-cookie-controlled-php.html
Publish Date: 2026-04-03 11:32:00
Source Domain: thehackernews.com
Threat actors are increasingly using HTTP cookies as a control channel for PHP-based web shells on Linux servers and to achieve remote code execution, according to findings from the Microsoft Defender Security Research Team.
“Instead of exposing command execution through URL parameters or request bodies, these web shells rely on threat actor-supplied cookie values to gate execution, pass instructions, and activate malicious functionality,” the tech giant said.
The approach offers added stealth as it allows malicious code to stay dormant during normal application execution and activate the web shell logic only when specific cookie values are present. This behavior, Microsoft noted, extends to web requests, scheduled tasks, and trusted background workers.
The malicious activity takes advantage of the fact that cookie values are available at runtime through the $_COOKIE superglobal variable, allowing attacker-supplied inputs to be consumed without additional parsing. What’s more, the technique is unlikely to raise any red flags as cookies blend into normal web traffic and reduce visibility.
The cookie-controlled execution model comes in different implementations –
- A PHP loader that uses multiple layers of obfuscation and runtime checks before parsing structured cookie input to execute an encoded secondary payload.
- A PHP script that segments structured cookie data to reconstruct operational components such as file handling and decoding functions, and conditionally writes a secondary payload to disk and executes it.
- A PHP script that uses a single cookie value as a marker to trigger threat actor-controlled actions, including execution of supplied input and file upload.
In at least one case, threat actors have been found to obtain initial access to a victim’s hosted Linux environment through valid credentials or the exploitation of a known security vulnerability to set up a cron job that invokes…
