![]() The figure above, which comes from Imperva’s 2020 Bad Bot Report, should come as a warning to all internet users, especially companies and organizations who maintain their own infrastructure online to take this problem seriously. In a default installation, we can see that all of the functions mentioned above are enabled.Note: This article, which was originally published in 2019, has been updated to include related news & media resources. If you are unsure whether they are enabled on your system, the following will return a list of the dangerous functions that are enabled. What is even more dangerous is that all these in-built PHP commands are enabled by default when PHP is installed and the majority of system administrators do not disable them. We have established that these functions (and a few others) can be very dangerous. It uses the system() function to execute commands that are being passed through ‘cmd’ HTTP request GET parameter. Note: The backtick character (`) should not to be confused with the single quote character (‘) $output" īased on the above, the following is a PHP web shell in its simplest form. Surprisingly, not many PHP developers are aware of this but PHP will execute the contents of backticks (`) as a shell command. By using proc_open(), we can create a handler (process) that will be used for communication between our script and the program that we want to run. ![]() The proc_open() function can be difficult to understand (you can find a detailed description of the function in the PHP docs). rw-rw-r- 1 secuser secuser 29 Feb 28 18:23 shell.php proc_open() ĭrwxrwxr-x 2 secuser secuser 4096 Feb 28 18:23. ![]() The passthru() function executes a command and returns output in raw format. rw-rw-r- 1 secuser secuser 36 Feb 28 18:24 shell.php The shell_exec() function is similar to exec(), however, it outputs the entire result as a string. ![]() => -rw-rw-r- 1 secuser secuser 49 Feb 27 20:54 shell.php ) shell_exec() => drwxrwxr-x 2 secuser secuser 4096 Feb 27 20:55. If a second parameter is specified, the result is returned in an array. > -rw-rw-r- 1 secuser secuser 29 Feb 27 20:49 shell.php Using echo with the exec() function will only print the last line of the command output. Otherwise, only the last line of the result will be shown if echoed. If a second optional parameter is specified, the result will be returned as an array. The exec() function accepts a command as a parameter but does not output the result. rw-rw-r- 1 secuser secuser 26 Feb 27 20:41 shell.php ĭrwxrwxr-x 2 secuser secuser 4096 Feb 27 20:43. Įxecuting the ls command on a Linux machine achieves a similar result. The following example on a Microsoft Windows machine will run the dir command to return a directory listing of the directory in which the PHP file is executed. The system() function accepts the command as a parameter and it outputs the result. Note: For the purposes of this article, we edited our hosts file and pointed the domain to a test server.
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