Automatically Generate Rulesets for Apache mod_rewrite or Nginx for Intelligent HTTP C2 Redirection

This project converts a Cobalt Strike profile to a functional mod_rewrite .htaccess or Nginx config file to support HTTP reverse proxy redirection to a Cobalt Strike teamserver. The use of reverse proxies provides protection to backend C2 servers from profiling, investigation, and general internet background radiation.

Note: You should test and tune the output as needed before deploying, but these scripts should handle the heavy lifting.

Features

• Now requires Python 3.0+
• Supports the Cobalt Strike custom URI features as of CS 4.0
• Rewrite Rules based on valid C2 URIs (HTTP GET, POST, and Stager) and specified User-Agent string.
  • Result: Only requests to valid C2 endpoints with a specified UA string will be proxied to the teamserver by default.
• Uses a custom Malleable C2 profile to build a .htaccess file with corresponding mod_rewrite rules
• Uses a custom Malleable C2 profile to build a Nginx config with corresponding proxy_pass rules
• HTTP or HTTPS proxying to the Cobalt Strike teamserver
• HTTP 302 Redirection to a Legitimate Site for Non-Matching Requests

Quick start

The havex.profile example is included for a quick test.

1. Run the script against a profile
2. Save the output to .htaccess or /etc/nginx/nginx.conf on your redirector
3. Modify as needed
4. Reload\restart the web server

Apache mod_rewrite Example Usage using a remote include file

python3 cs2modrewrite.py -i havex.profile -c https://TEAMSERVER -r https://GOHERE -o /etc/apache2/redirect.rules

Example Apache Config

<VirtualHost *:80>
    ServerAdmin webmaster@localhost
    DocumentRoot /var/www/html
    RemoteIPHeader X-Forwarded-For

    ErrorLog /var/log/apache2/redirector_error.log
    CustomLog /var/log/apache2/redirector_access.log combined
    ErrorDocument 401 " "
    ErrorDocument 403 " "
    ErrorDocument 404 " "
    ErrorDocument 500 " "
    ErrorDocument 503 " "

    # Include redirect.rules
    Include /etc/apache2/redirect.rules
</VirtualHost>

Consider Updating Apache Server Header, ServerTokens, and logging with something like the following.

## Update Apached Server Header, ServerTokens, and logging
echo "Update Update Apached Server Header, ServerTokens, and logging"
sed -i -e 's/\(ServerTokens\s\+\)OS/\1Prod/g' /etc/apache2/conf-enabled/security.conf
sed -i -e 's/\(ServerSignature\s\+\)On/\1Off/g' /etc/apache2/conf-enabled/security.conf
echo "SecServerSignature Server" >> /etc/apache2/conf-enabled/security.conf
echo "LogLevel alert rewrite:trace2" >> /etc/apache2/conf-enabled/security.conf

## Update Apached remoteip.conf
echo "Update Apached remoteip.conf"
echo "RemoteIPHeader X-Forwarded-For" >> /etc/apache2/conf-enabled/remoteip.conf

## Restart apache server
echo "Restart apache server"
systemctl restart apache2

Apache mod_rewrite Example Usage using a .htaccess file

python3 cs2modrewrite.py -i havex.profile -c https://TEAMSERVER -r https://GOHERE -o /var/www/html/.htaccess

Apache Rewrite Setup and Tips

Enable Rewrite and Proxy

apt-get install apache2
a2enmod rewrite headers proxy proxy_http ssl cache
a2dismod -f deflate
service apache2 reload

Note: https://bluescreenofjeff.com/2016-06-28-cobalt-strike-http-c2-redirectors-with-apache-mod_rewrite/ "e0x70i pointed out in the comments below that if your Cobalt Strike Malleable C2 profile contains an Accept-Encoding header for gzip, your Apache install may compress that traffic by default and cause your Beacon to be unresponsive or function incorrectly. To overcome this, disable mod_deflate (via a2dismod deflate and add the No Encode ([NE]) flag to your rewrite rules. (Thank you, e0x70i!)"

Enable SSL support

Ensure the following entries are in the site's config (i.e. /etc/apache2/available-sites/*.conf)

# Enable SSL
SSLEngine On
# Enable SSL Proxy
SSLProxyEngine On
# Trust Self-Signed Certificates generated by CobaltStrike
SSLProxyVerify none
SSLProxyCheckPeerCN off
SSLProxyCheckPeerName off
SSLProxyCheckPeerExpire off

.HTACCESS

If you plan on using mod_rewrite in .htaccess files (instead of the site's config file), you also need to enable the use of .htaccess files by changing AllowOverride None to AllowOverride All. For all websites, edit /etc/apache2/apache.conf

<Directory /var/www/>
    Options FollowSymLinks MultiViews
    AllowOverride All
    Order allow,deny
    allow from all
</Directory>

Finally, restart apache once more for good measure.

service apache2 restart

Troubleshooting

If you need to troubleshoot redirection rule behavior, enable detailed error tracing in your site's configuration file by adding the following line.

LogLevel alert rewrite:trace5

Next, reload apache, and monitor /var/log/access.log /var/log/error.log to see which rules are matching.

---

Nginx Example Usage

Install Nginx

apt-get install nginx nginx-extras

Note: nginx-extras is needed for custom server headers. If you can't get this package, then comment out the server header line in the resulting configuration file.

Create Redirection Rules

Save the cs2nginx.py output to /etc/nginx/nginx.conf and modify as needed (SSL parameters).

python3 ./cs2nginx.py -i havex.profile -c https://127.0.0.1 -r https://www.google.com -H mydomain.local >/etc/nginx/nginx.conf

Finally, restart nginx after modifying the server configuration file.

service nginx restart

Final Thoughts

Once redirection is configured and functioning, ensure your C2 servers only allow ingress from the redirector and your trusted IPs (VPN, office ranges, etc).

Consider adding additional redirector protections using GeoIP restrictions (mod_maxmind) and blacklists of bad user agents and IP ranges. Thanks to @curi0usJack for the ideas.

References

• Joe Vest and Andrew Chiles - cs2modrewrite.py blog post

• @bluescreenofjeff - Cobalt Strike HTTP C2 Redirectors with Apache mod_rewrite

• Adam Brown - Resilient Red Team HTTPS Redirection Using Nginx

• Apache - Apache mod_rewrite Documentation