RedWarden - Flexible CobaltStrike Malleable Redirector

(previously known as proxy2's malleable_redirector plugin)

Let's raise the bar in C2 redirectors IR resiliency, shall we?

Red Teaming business has seen several different great ideas on how to combat incident responders and misdirect them while offering resistant C2 redirectors network at the same time.

This work combines many of those great ideas into a one, lightweight utility, mimicking Apache2 in it's roots of being a simple HTTP(S) reverse-proxy.

Combining Malleable C2 profiles understanding, knowledge of bad IP addresses pool and a flexibility of easily adding new inspection and misrouting logic - resulted in having a crafty repellent for IR inspections.

Should any invalid inbound packet reach RedWarden - you can redirect, reset or just proxy it away!

Abstract

This program acts as a HTTP/HTTPS reverse-proxy with several restrictions imposed upon inbound C2 HTTP requests selecting which packets to direct to the Teamserver and which to drop, similarly to the .htaccess file restrictions mandated in Apache2's mod_rewrite.

RedWarden was created to solve the problem of IR/AV/EDRs/Sandboxes evasion on the C2 redirector layer. It's intended to supersede classical Apache2 + mod_rewrite setups used for that purpose.

Features:

• Malleable C2 Profile parser able to validate inbound HTTP/S requests strictly according to malleable's contract and drop outlaying packets in case of violation (Malleable Profiles 4.0+ with variants covered)
• Ability to unfilter/repair unexpected and unwanted HTTP headers added by interim systems such as proxies and caches (think CloudFlare) in order to conform to a valid Malleable contract.
• Integrated curated massive blacklist of IPv4 pools and ranges known to be associated with IT Security vendors
• Grepable output log entries (in both Apache2 combined access log and custom RedWarden formats) useful to track peer connectivity events/issues
• Ability to query connecting peer's IPv4 address against IP Geolocation/whois information and confront that with predefined regular expressions to rule out peers connecting outside of trusted organizations/countries/cities etc.
• Built-in Replay attacks mitigation enforced by logging accepted requests' MD5 hashsums into locally stored SQLite database and preventing requests previously accepted.
• Allows to define ProxyPass statemtents to pass requests matching specific URL onto other Hosts
• Support for multiple Teamservers
• Support for many reverse-proxying Hosts/redirection sites giving in a randomized order - which lets load-balance traffic or build more versatile infrastructures
• Can repair HTTP packets according to expected malleable contract in case some of the headers were corrupted in traffic
• Sleepless nights spent on troubleshooting "why my Beacon doesn't work over CloudFlare/CDN/Domain Fronting" are over now thanks to detailed verbose HTTP(S) requests/responses logs

The RedWarden takes Malleable C2 profile and teamserver's hostname:port on its input. It then parses supplied malleable profile sections to understand the contract and pass through only those inbound requests that satisfied it while misdirecting others.

Sections such as http-stager, http-get, http-post and their corresponding uris, headers, prepend/append patterns, User-Agent are all used to distinguish between legitimate beacon's request and unrelated Internet noise or IR/AV/EDRs out of bound packets.

The program benefits from the marvelous known bad IP ranges coming from: curi0usJack and the others: https://gist.github.com/curi0usJack/971385e8334e189d93a6cb4671238b10

Using an IP addresses blacklisting along with known bad keywords lookup through Reverse-IP DNS queries and HTTP headers inspection, brings the reliability to considerably increase redirector's resiliency to the unauthorized peers wanting to examine attacker infrastructures.

Invalid packets may be misrouted according to three strategies:

• redirect: Simply redirect peer to another websites, such as Rick Roll.
• reset: Kill TCP connection straightaway.
• proxy: Fetch a response from another website, to mimic cloned/hijacked website as closely as possible.

This configuration is mandated in configuration file:

#
# What to do with the request originating not conforming to Beacon, whitelisting or 
# ProxyPass inclusive statements: 
#   - 'redirect' it to another host with (HTTP 301), 
#   - 'reset' a TCP connection with connecting client
#   - 'proxy' the request, acting as a reverse-proxy against specified action_url 
#       (may be dangerous if client fetches something it shouldn't supposed to see!)
#
# Valid values: 'reset', 'redirect', 'proxy'. 
#
# Default: redirect
#
drop_action: redirect

Below example shows outcome of redirect to https://googole.com:

Use wisely, stay safe.

Requirements

This program can run only on Linux systems as it uses fork to spawn multiple processes.

Also, the openssl system command is expected to be installed as it is used to generate SSL certificates.

Finally, install all of the Python3 PIP requirements easily with:

bash $ sudo pip3 install -r requirements.txt

Usage

Example usage

The minimal RedWarden's config.yaml configuration file could contain:

port:
  - 80/http
  - 443/https

profile: jquery-c2.3.14.profile

ssl_cacert: /etc/letsencrypt/live/attacker.com/fullchain.pem
ssl_cakey: /etc/letsencrypt/live/attacker.com/privkey.pem

teamserver_url:
  - 1.2.3.4:8080

drop_action: reset

Then, the program can be launched by giving it a path to the config file:

bash$ sudo python3 RedWarden.py -c config.yaml

  [INFO] 19:21:42: Loading 1 plugin...
  [INFO] 19:21:42: Plugin "malleable_redirector" has been installed.
  [INFO] 19:21:42: Preparing SSL certificates and keys for https traffic interception...
  [INFO] 19:21:42: Using provided CA key file: ca-cert/ca.key
  [INFO] 19:21:42: Using provided CA certificate file: ca-cert/ca.crt
  [INFO] 19:21:42: Using provided Certificate key: ca-cert/cert.key
  [INFO] 19:21:42: Serving http proxy on: 0.0.0.0, port: 80...
  [INFO] 19:21:42: Serving https proxy on: 0.0.0.0, port: 443...
  [INFO] 19:21:42: [REQUEST] GET /jquery-3.3.1.min.js
  [INFO] 19:21:42: == Valid malleable http-get request inbound.
  [INFO] 19:21:42: Plugin redirected request from [code.jquery.com] to [1.2.3.4:8080]
  [INFO] 19:21:42: [RESPONSE] HTTP 200 OK, length: 5543
  [INFO] 19:21:45: [REQUEST] GET /jquery-3.3.1.min.js
  [INFO] 19:21:45: == Valid malleable http-get request inbound.
  [INFO] 19:21:45: Plugin redirected request from [code.jquery.com] to [1.2.3.4:8080]
  [INFO] 19:21:45: [RESPONSE] HTTP 200 OK, length: 5543
  [INFO] 19:21:46: [REQUEST] GET /
  [...]
  [ERROR] 19:24:46: [DROP, reason:1] inbound User-Agent differs from the one defined in C2 profile.
  [...]
  [INFO] 19:24:46: [RESPONSE] HTTP 301 Moved Permanently, length: 212