Building C2 Redirector Infrastructure

What it does

When your agent uses it

• Standing up red-team C2 that must survive blue-team triage
• Ensuring only profile-matching implant traffic reaches the hidden team server

Example prompts

• “/building-c2-redirector-infrastructure”

Requirements

• Python 3

Workflow steps

7 steps, taken from the step headings in SKILL.md.

1. 1Lab and firewall the team server
2. 2Dumb-pipe redirector (socat / iptables)
3. 3Filtering nginx reverse-proxy redirector
4. 4Apache mod_rewrite redirector
5. 5Generate rules from a malleable profile
6. 6Terminate TLS with Let's Encrypt
7. 7Apply OPSEC controls

What it can do on your machine

Read from SKILL.md and the folder at commit 54a7988. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Ships 1 file in scripts/ (Python), which the agent can run.

  Shell commands in SKILL.md call:

  • apt
  • python3
  • curl
  • git

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Hosts in commands or code, which the agent is likely to contact:

  • legitimate-decoy.com
  • github.com

  Also links to:

  • nginx.org
  • httpd.apache.org
  • dest-unreach.org
  • certbot.eff.org
  • ired.team

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Building C2 Redirector Infrastructure loads about 2.9k tokens when it runs, and up to ~3.9k if it reads all its reference files. Until then it costs about 110 tokens; SKILL.md has 921 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~110

When it runs · the whole SKILL.md, loaded when a task matches

~2.9k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~3.9k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

• NoteRuns commands with sudoSKILL.md:50

  sudo apt update

• NoteRuns commands with sudoSKILL.md:51

  sudo apt install -y nginx apache2 socat certbot python3-certbot-nginx git

• NoteRuns commands with sudoSKILL.md:53

  sudo a2enmod rewrite proxy proxy_http ssl headers

• NoteRuns commands with sudoSKILL.md:87

  sudo ufw default deny incoming

• NoteRuns commands with sudoSKILL.md:88

  sudo ufw allow from 203.0.113.10 to any port 443 proto tcp

• NoteRuns commands with sudoSKILL.md:89

  sudo ufw allow OpenSSH

• NoteRuns commands with sudoSKILL.md:90

  sudo ufw enable

• NoteRuns commands with sudoSKILL.md:135

  sudo ln -s /etc/nginx/sites-available/redirector.conf /etc/nginx/sites-enabled/

• NoteRuns commands with sudoSKILL.md:136

  sudo nginx -t && sudo systemctl reload nginx

• NoteRuns commands with sudoSKILL.md:155

  sudo a2ensite redirector && sudo apache2ctl configtest && sudo systemctl reload apache2

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); the scripts in this folder are not scanned.

SKILL.md

The full file from mukul975/Anthropic-Cybersecurity-Skills at commit 54a7988, republished under its Apache-2.0 licence (© mukul975). 921 words, ~2,899 tokens.

name

building-c2-redirector-infrastructure

description

Build dumb-pipe and traffic-filtering C2 redirectors with nginx (proxy_pass) and Apache (mod_rewrite), deriving filter rules from a Malleable C2 profile, layering Let's Encrypt TLS, and applying OPSEC controls like domain fronting and UA/geo filtering. Use when standing up red-team C2 that must survive blue-team triage or ensuring only profile-matching implant traffic reaches the hidden team server.

domain

cybersecurity

subdomain

red-teaming

tags

red-team, c2-infrastructure, redirector, nginx, apache-mod-rewrite, malleable-c2, opsec, traffic-filtering

version

1.0

author

mahipal

license

Apache-2.0

nist_csf

DE.CM-01

mitre_attack

T1090.002

# On the team server: only the redirector (203.0.113.10) may reach 443/tcp
sudo ufw default deny incoming
sudo ufw allow from 203.0.113.10 to any port 443 proto tcp
sudo ufw allow OpenSSH
sudo ufw enable

# socat foreground forward of 443 -> team server
socat TCP4-LISTEN:443,fork,reuseaddr TCP4:10.0.0.2:443

# Or iptables DNAT (persistent)
sysctl -w net.ipv4.ip_forward=1
iptables -t nat -A PREROUTING -p tcp --dport 443 -j DNAT --to-destination 10.0.0.2:443
iptables -t nat -A POSTROUTING -p tcp -d 10.0.0.2 --dport 443 -j MASQUERADE

# /etc/nginx/sites-available/redirector.conf
server {
    listen 443 ssl;
    server_name cdn.example.com;

    ssl_certificate     /etc/letsencrypt/live/cdn.example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/cdn.example.com/privkey.pem;

    # Proxy ONLY profile-matching C2 URIs to the hidden team server
    location ~ ^/(api/v2/jobs|cm/[a-z0-9]+|push) {
        # Require the implant's exact User-Agent
        if ($http_user_agent != "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36") {
            return 302 https://www.legitimate-decoy.com/;
        }
        proxy_pass https://10.0.0.2;
        proxy_ssl_verify off;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $remote_addr;
    }

    # Everything else -> benign decoy
    location / {
        return 302 https://www.legitimate-decoy.com/;
    }
}

sudo ln -s /etc/nginx/sites-available/redirector.conf /etc/nginx/sites-enabled/
sudo nginx -t && sudo systemctl reload nginx

# /etc/apache2/sites-available/redirector.conf  (inside <VirtualHost *:443>)
RewriteEngine On
SSLProxyEngine On
# Require the implant User-Agent
RewriteCond %{HTTP_USER_AGENT} "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36" [NC]
# Match valid C2 URIs (GET/POST/stager) from the malleable profile
RewriteCond %{REQUEST_URI} ^/(api/v2/jobs|cm/[a-z0-9]+|push)/?$
# Proxy to the hidden team server, preserving the URI
RewriteRule ^.*$ https://10.0.0.2%{REQUEST_URI} [P,L]
# Everything else -> decoy site
RewriteRule ^.*$ https://www.legitimate-decoy.com/ [R=302,L]

sudo a2ensite redirector && sudo apache2ctl configtest && sudo systemctl reload apache2

cd cs2modrewrite
# Apache mod_rewrite rules
python3 cs2modrewrite.py -i havex.profile -c https://10.0.0.2 \
  -r https://www.legitimate-decoy.com -o /etc/apache2/redirect.rules
# nginx config
python3 cs2nginx.py -i havex.profile -c https://10.0.0.2 \
  -r https://www.legitimate-decoy.com -H cdn.example.com > /etc/nginx/sites-available/c2.conf

sudo certbot --nginx -d cdn.example.com --agree-tos -m ops@example.com --redirect
# Verify auto-renewal
sudo certbot renew --dry-run

# Example: drop non-target geographies at the firewall with ipset/GeoIP,
# require a custom auth header in the profile, and rotate the redirector
# domain/IP on a schedule. Check the redirector only forwards matched traffic:
curl -k https://cdn.example.com/                       # expect 302 to decoy
curl -k -A "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36" \
  https://cdn.example.com/api/v2/jobs                  # expect proxied response

© mukul975, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 4 other files (scripts, references) in skills/building-c2-redirector-infrastructure of mukul975/Anthropic-Cybersecurity-Skills.

• SKILL.md
• LICENSE
• references/api-reference.md
• references/standards.md
• scripts/agent.py

Open the folder on GitHubat commit 54a7988