Mitigate the Security Risks of PHP System Command Execution

"The risks of not properly vetting operating system commands initiated through a PHP script are no less severe! With this in mind, before jumping into a few examples it's worth taking a moment to understand how this particular feature can pose a significant security risk to not only your web site, but also to the stability of the entire web server.

"When PHP is installed as an Apache module, it operates on behalf of the system user (which has assumed ownership of the Apache daemon). This means that when PHP executes an operating system command, the Apache daemon owner carries out that command. Therefore, any permissions assigned to the Apache daemon owner are applied when executing this command. Some improperly configured servers actually run Apache using the root user, meaning an errant PHP script could conceivably delete large parts of the operating system and any data stored within! Even in the more likely case of your server operating on behalf of a non-root user, the security risks remain nonetheless severe."

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