👉 Overview
👀 What ?
The 'disable_functions bypass - Imagick <= 3.3.0 PHP >= 5.4 Exploit' is a cybersecurity vulnerability that allows an attacker to bypass disabled functions in PHP through the Imagick extension. The flaw resides in versions of Imagick up to 3.3.0 and PHP versions 5.4 and above.
🧐 Why ?
Understanding this exploit is crucial as it could potentially allow an attacker to execute arbitrary code or commands on affected systems, leading to unauthorized access, data breaches, or even system crashes. It's particularly important for developers and system administrators who need to ensure the security of their PHP applications and servers.
⛏️ How ?
To exploit this vulnerability, an attacker would first need to identify a target system running the vulnerable versions of Imagick and PHP. They would then craft a malicious request designed to bypass the 'disable_functions' directive in PHP, enabling them to execute the disabled functions. To protect against this exploit, users should update their PHP and Imagick to the latest versions where this vulnerability has been patched. Additionally, it's also recommended to restrict the permissions of the PHP process and limit the exposure of the application to the internet.
⏳ When ?
The exploitation of this vulnerability began to be noticed in the cybersecurity community around late 2015, after the release of Imagick 3.3.0.
⚙️ Technical Explanations
The 'disable_functions' directive in PHP is a security feature intended to disable certain sensitive functions that could be exploited by an attacker. In the vulnerable versions of Imagick, a certain function did not correctly adhere to this directive, allowing an attacker to bypass it. Specifically, the 'Imagick::readImage' function was found to be vulnerable to a protocol handler abuse attack, where an attacker could specify a data protocol handler (e.g., data://) to execute arbitrary shell commands. This exploit highlights the importance of careful input validation and function restrictions in application and extension development.