👉 Overview
👀 What ?
disable_functions bypass in PHP is a technique used to execute commands on a server, even when certain PHP functions have been disabled for security reasons. The pcntl_exec function, available in PHP 4.2.0 and onwards, is one function that can be used for this purpose.
🧐 Why ?
Understanding disable_functions bypass is crucial for developers and cybersecurity professionals alike. Developers need to be aware of it to ensure that they are not inadvertently creating security vulnerabilities in their PHP applications. Cybersecurity professionals need to understand it to protect systems from attacks that use this technique.
⛏️ How ?
A disable_functions bypass can be performed using the pcntl_exec function in PHP. The function takes two arguments: the program to be executed and an array of arguments to pass to the program. By calling this function, one can execute a command on the server, even if the 'exec' function (or other similar functions) have been disabled in the PHP configuration.
⏳ When ?
The pcntl_exec function was introduced in PHP version 4.2.0, released in April 2002, and has been available in all subsequent versions of PHP. Its potential for use in disable_functions bypasses was not widely recognized until much later.
⚙️ Technical Explanations
The disable_functions directive in the PHP configuration file (php.ini) allows system administrators to disable certain PHP functions that can be used to execute commands on the server, in an effort to prevent command injection attacks. However, this directive is not foolproof. One way to bypass it is by using the pcntl_exec function, which is not usually included in the disable_functions list. This function executes a program in a new process, which can be used to run a command on the server. Note that pcntl_exec function is only available when PHP is compiled with the '--enable-pcntl' configuration option, and it is not available on Windows platforms.