Posts

Introducing PoshC2 v5.0

PoshC2 v5.0 is here and there are significant changes and improvements that we’re very excited to reveal!  There’s been a move to Python3, much improved documentation, significant functionality and quality of life improvements, and more.  Read on for a detailed description of it all!

Repositories

We have had a bit of a change around with repository names, as described here.

This brings us back to PoshC2 being the latest and greatest repository, and PoshC2_old being the obsolete repository.

Documentation

The documentation for PoshC2 has been completely re-written and updated, with emphasis on red team trade-craft when using PoshC2 and on extending and customising it to suit any situation or environment.

It will still be updated regularly, but there will be less focus on what all the different techniques are, and more on how to use PoshC2 itself. Check it out at https://poshc2.readthedocs.io.

Python3

PoshC2 has been completely updated to use Python3. With Python2 becoming End-of-Life in January 2020, it was quite an important change to make.

Posh Commands

Efforts have been made to abstract the potentially difficult nuances of setting up and using PoshC2 away from the user.  Remember having to change into the PoshC2 directory, setup and use a Python virtual environment, to avoid dependency version clashes with the rest of your system?  That’s a thing of the past.

The install script now installs a number of posh-* commands to your /usr/bin directory, before setting up the virtual environment ahead of time. These scripts then encapsulate the use of that environment for the user, allowing PoshC2 to be run and configured from any directory, and it will seamlessly use the virtual environment and other configurations behind the scenes.

For example, PoshC2 can be configured from any directory using your editor of choice by issuing:

posh-config

It can then be installed and run as a service simply by executing:

posh-service

Conversely so it can be stopped using:

posh-stop-service

The Implant-Handler can now be started using posh with a username which is used for logging purposes:

posh u crashoverride

…and you’re good to go.

Use of these scripts is recommended, as any further logic will also go into them and we will work to ensure that PoshC2 works seamlessly when they are used, while other techniques may not be maintained.

Prompt

PoshC2 now has an intelligent new prompt that can aid users when performing red teaming!

https://poshc2.readthedocs.io/en/latest/_images/autocompletions.png

This prompt has context-sensitive auto-completions, intelligently suggesting commands based on the current prompt, such as PowerShell commands in a PowerShell prompt and so on. A unique command history is stored per context, so you won’t have to scroll back through PowerShell commands on a C# implant.

https://poshc2.readthedocs.io/en/latest/_images/autosuggestions.png

In addition to this, the prompt features fish-shell-like auto-suggestions in dark grey text based on commands from that prompt’s history, so if you want to repeat or edit log commands you can complete the suggestion by pressing the right-arrow key or ctrl+e.

Combined with the help and searchhelp commands, we hope that this will allow users of PoshC2 to quickly explore PoshC2s functionality and enable veteran users efficiency and speed of operation for those crucial engagements.

SharpSocks

SharpSocks has undergone some significant improvements and integration into PoshC2. It started out as a standalone cmdlet that can be initiated from any PS session, but we have now fully integrated this so the users can be in any implant and type sharpsocks to get this going. A full separate blog has been written with all the changes for SharpSocks and can be found here:

Introducing SharpSocks v2.0

New Payloads

Several new payloads have been added out-of-the-box, including a DotNet2JS payload using James Forshaw’s DotNet2JScript technique, and a new C# payload for PowerShell Implants.

Sharp Implant Improvements

AMSI Bypass

.NET 4.8 introduced Antimalware scanning for all assemblies, including those loaded using Assembly.Load(byte[] bytes), which previously went unchecked and is used by our PowerShell-less C# implant to load C# executables and run them in memory.

This release features a new bypass-amsi command for the C# implant which will patch AMSI in memory and allow flagged modules to be loaded and executed.

Aliases

We fully appreciate that nobody has time to type out long commands over and over. To that end, we’ve streamlined the run-exe commands for the C# Implant. Now, instead of run-exe Seatbelt.Program Seatbelt all it’s just seatbelt all.

We’ve added aliases for all our favourite commands, but you can add your own in Alias.py. See the documentation for more details.

Lateral Movement Methods

In addition to integrating SharpSocks, we’ve integrated PBind, another great tool written by Doug McLeod. This is now full integrated into PoshC2 and users can type invoke-wmijspbindpayload with the relevant arguments to try and attempt execution on another endpoint using SMB named pipes. The default SMB named pipe for PoshC2 is jaccdpqnvbrrxlaf.

invoke-wmijspbindpayload -target  -domain  -user  -pass ''

In addition to the lateral movement command, PoshC2 will automatically create several payloads that are named PBind payloads. These, like the normal payloads, can be executed against a remote host in whichever technique you prefer to use; dcom, wmi, psexec, etc.

Once you have initiated the payload on a remote host, it will automatically open an SMB named pipe ready for connection. You must know the secret key, the encryption key and the pipe name to communicate, but we already have you covered for this as it tells you what commands to run to interact with the PBind implant:

If you want any other information on PBind, a previous blog covers the techniques in more details and the comms methods including a diagram.

https://labs.nettitude.com/blog/extending-c2-lateral-movement-invoke-pbind/

FPC script

Amongst the various scripts that are added to /usr/bin is the fpc (Find PoshC2 Command) script, added to aid in reporting. This script allows you to search for PoshC2 commands, filtering on keywords in the command, the command output and by user.

Credential management

We’ve improved the credential management in PoshC2, and now when you run Mimikatz’s logonpasswords, the credentials will automatically be parsed and stored in the database, and can be displayed or manipulated using the creds command.

Remainder

There’s also a myriad other improvements such as to logging, tracking file hashes on upload, UX improvements, internal modularisation and refactoring and module updates, with a lot more in the pipeline to come. Stay tuned on Twitter (@Nettitude_Labs, @benpturner, @m0rv4i) for the latest updates or join the PoshC2 slack channel by emailing labs at nettitude dot com.

Roadmap

There’s a lot planned for PoshC2 but the main upcoming features are detailed below.

Docker

The bad news is that support for any platform other than Debian flavours of Linux has been retired. While PoshC2 is written in Python3 and can be maintained to work across multiple platforms, we have instead elected to only support Debian-based distributions.  However, we are working to bring Docker support to PoshC2 to add the ability to run PoshC2 from a Docker container, allowing full and stable execution across any platform that supports Docker, including Windows and Mac OSX.

A docker branch has been created with a Dockerfile added in addition to a number of Docker commands that can be used to manage the containers, but this is still very much in an unstable format.

OpSec

One of the biggest concerns when running a red team engagement is operational security, and to that end we’re working on improving both the offensive side by making more of the inner workings of PoshC2 configurable, but also the reporting side by improving file upload tracking, hosts and users compromised and so on.

This will complement improvements to the HTML report and improve the OpSec and reporting side of things considerably.

Full changelist

The full changelist is below:

  • Added Harmj0y’s KeeThief to modules
  • Added RastaMouse’s Watson to modules
  • Added SafetyDump for minidumping in memory
  • Added file hashing when a file is uploaded
  • Rework imports to improve dependency management
  • Break up ImplantHandler into PSHandler.py, PyHandler.py and SharpHandler.py
  • Add ability to upload a file to an ADS
  • Update BloodHound
  • Pull out unpatched payloads into file for easy management
  • Add base64 encoded versions of the shellcode to the payloads directory
  • Add a configurable jitter to all implants
  • Update the notifications config if it is changed in the Config.py
  • Add NotificationsProjectName in Config.py which is displayed in notifications message
  • Add fpc script which searches the Posh DB for a particular command
  • Modify InjectShellcode logged command to remove base64 encoded shellcode and instead just log loaded filename
  • Add aliases for common sharp modules
  • Fix Shellcode_migrate payload creation
  • Start randomuris with a letter then proceed with random letters and numbers as e.g. msbuild errors if task name starts with a number
  • Fix issue with cred-popper and keylogger using same variable and conflicting
  • Add SCF files to the opsec command
  • Add posh commands on *nix for abstracting the use of pipenv and set up the env in the install script.
  • Move to python3 as python2 is EoL in 2020
  • Misc performance improvments, such as reduced cylomatic complexity and only processing the command once per input
  • Store creds in the DB, add ability to add creds/have them automatically parsed from mimikatz and add ability to specify use of a credId for some commands
  • Add create-shortcut command
  • Don’t show powershell one liner when domain fronting as it tries to connect directly
  • Added set-killdate command
  • Added posh-stop-service linux command
  • Updated Mimikatz
  • Added SafetyKatz
  • posh-config uses $EDITOR variable
  • New Sharp_Powershell_Runner payload compilation with mono
  • Added DotNet2JS Payload generation
  • Added get-computerinfo and get-dodgyprocesses to c# core
  • Misc small fixes
  • Updated help and readme
  • Add new prompt with intelligent autocompletions, autosuggestions and smart history
  • Log when a user logs on or logs off in the C2 server output
  • Add ability to broadcast messages in the C2 server output using the ‘message’ command
  • Add quit commands to Sharp and Python handlers
  • output-to-html renamed to generate-reports
  • Force setting of username for logging
  • Show Implant type at Implant prompt
  • Update User Agent string to match current Chrome
  • Added New SharpSocks
  • Addd * suffix for usernames for High Integrity processes
  • Added lateral movements to Sharp Implant (SMB/DCOM/WMI)
  • Add AMSI bypass for C# Implant
  • Updated PBIND hosts in opsec
  • Added invoke-mimikatz output from PBIND to be parsed
  • Updated PBIND to send stderror if the command does not work
  • Added remove-label for implants
  • Updated PSHandler to add DomainFrontURL to sharpsocks if in use
  • Updated RunAs-NetOnly
  • Added RunAs-NetOnly which uses SimpleImpersonation to create a token
  • Removed print statement on pbind-loadmodule
  • Updated pbind-command and pbind-module
  • Updated the pbind commands
  • Updated invoke-wmijspbindpayload
  • Added PBind payloads to PoshC2
  • Updated opsec error when username is None
  • Add output-to-html retired message
  • Add Matterpreter’s Shhmon
  • Updated ‘tasks’ command to add ImplantID
  • List PowerShell modules pretty like C# modules
  • Add new Sharp modules
  • Port the .NET AMSI Bypass to PowerShell
  • Updated Get-ScreenshotMulti to Continue if Screen is Locked
  • Correct Jitter time equation in PS implant
  • Print last commit and timestamp in header
  • Prompt improvements
  • Updated C2Server / SharpSocks Error responses
  • Updated HTML output
  • Update fpc.py to use virtualenv and only copy fpc to /usr/bin
  • Updated help
  • Expand on opsec no-nos
  • Update inject-shellcode help

Extending C2 Lateral Movement – Invoke-Pbind

Invoke-Pbind is a mini post exploitation framework written in PowerShell, which builds C2 communications over SMB named pipes using a push rather than a pull mechanism. Pbind was initially created to overcome lateral movement problems, specifically in restricted environments where the server VLAN could not directly talk to the user VLAN (as it should be in every environment). The tool was designed to be integrated with any C2 framework or run as a standalone PowerShell script.

Video Demonstration

If you just want to skip to the video tutorial, then you can find that here and at the end of this post.

The Problem: Segregation and Strict Firewalling

This is useful when you have compromised an organisation and have C2 comms over HTTPS, traversing the corporate proxy server out of the network from user’s workstations, but the target dataset that you are looking to obtain is located down server VLAN with a firewall restricting both inbound and outbound traffic. In that scenario, firewall rules are always going to allow for specific traffic to traverse over pre-approved services. The following diagram illustrates one such situation, where the environment allows limited services from the user VLAN to the server VLAN, but allows no ports in the reverse direction.

What options exist for C2 comms

The following are some options for C2 comms and their mitigations, resulting in failure.

Method Mitigation Result
Direct Internet Access Blocked by Firewall Outbound Fail
Traverse Through HTTP Proxy Blocked by Firewall Outbound Fail
TCP Reverse Shell Blocked or likely detected scanning for open ports Fail
TCP Bind Shell Blocked by Firewall Inbound or service running on open ports, no closed ports detected Fail
ICMP Blocked by Firewall Outbound Fail
Daisy over SMB in User VLAN TCP port 445 blocked from servers to workstations Fail
Daisy over HTTP in User VLAN Same as standard reverse all blocked ports Fail
DNS Authoritive DNS is only permitted by the Proxy server, thus not possible for C2 comms from the server VLAN. Fail

To be clear, at this point the problem isn’t about getting execution, it’s about having reliable C2 comms that afford the user output for all commands executed and to use the implant as a foothold or staging point to further attacks against servers in the restricted environment.

The Solution

“A named pipe is a logical connection, similar to a Transmission Control Protocol (TCP) session, between the client and server that are involved in the CIFS/SMB connection. The name of the pipe serves as the endpoint for the communication, in the same manner as a port number serves as the endpoint for TCP sessions. This is called a named pipe endpoint.” – https://msdn.microsoft.com/en-us/library/cc239733.aspx.

.NET has a class for creating and interacting with named pipes:

Where TCP port 445 is open into a server environment, we can overlay the SMB protocol and use a named pipe to share data between the workstation and server, providing a method for exchanging data (comms). The following commands make up the basis of creating a named pipe with an access rule that allows “everyone” access:

Since the days of abusing IPC$ with anonymous access (CVE-199-0519), and RID cycling your way to a plethora of goodies, Microsoft have said “no – though shall not pass” – non Microsoft direct quote. In a domain environment, any user can create a domain authenticated session to the $IPC share, which can then be piggy backed to gain access to the named pipe. Here is a simple script in PowerShell to create an authenticated session. One quick problem to overcome: While the ‘AccessRule’ applied to the pipe may look like it allows “everyone” access to the named pipe, this is not actually the case.

Interacting with a named pipe is also fairly straight forward as long as you know the data type of what is being read; as we create the server we know how to handle to pipe as shown by using a simple StreamReader:

Design

When we came up with Invoke-Pbind, the following principles were implemented.

Client/Server Model

To allow for inclusion in a C2 framework, two script blocks were created, client and server. The server starts and sets up the named pipe on a remote target (server). The client then connects to the named pipe and exchanges messages over TCP port 445 (SMB). The client runs through an existing C2 implant and by using script blocks and run spaces, it is possible to use the client non-interactively for better interaction with most C2 frameworks.

Token Passing

When sharing a common space such as a named pipe, it is imperative that messages exchanged between the client and server are not overwritten prior to being picked up by their counterpart. Control messages are used in combination with TRY and IF statements to create rules for when a client or server should read or write from the named pipe.

Security

During the generation of the script blocks, at run time, a unique key is generated and used to encrypt messages between client and server. Pbind supports AES 256 encryption. To initiate a connection to the named pipe from a client, a shared secret is also supported to stop tampering with the named pipe. If the client does not provide the correct secret, the named pipe will close.

Injection/Execution

There are two main methods included that inject the implant into target hosts. These are modified versions of Invoke-WMIExec and Invoke-SMBExec (credit to Kevin Robertson for these scripts); both scripts have been updated to support passing passwords, where previously they only accepted hashes for authentication. The implant is a self-executing script block that is passed as the payload. The script runs WMIExec by default but contains a switch parameter to invoke SMBExec:

To provide additional deployment flexibility the script also includes an exe method. This method uses CSC and Windows .Net automation DLL to compile the implant into an executable that can then be deployed and executed through any means.

NOTE: Creating a named pipe does not require administrator credentials so the executable can be run as a non-privileged user. On the other hand, WMIExec and SMBExec require administrator privileges.

The exe option continues to generate unique variables that are hardcoded into the executable, for use in cryptography and such like. The exe option can be used offline to create an executable implant and is not tied to an interactive session through a C2. To talk to the implant, the script supports a CLIENT option that is used to interact with a deployed implant, the options for which are provided when the implant is compiled:

This flexibility allows for the deployment through any means:

  • DCOM
  • RDP
  • Shared Folders
  • WinRM
  • SCCM
  • Anything……

There are a number of options that are configurable. If no options are selected, the script reverts to pre-set or randomly generated values. The following options are configurable:

  • KEY – Defaults to a randomly generated AES 256 Key – Allows for a key to be specified, commonly used in client mode.
  • SECRET – Defaults to random 5 character value – Allows for specific secret to be used.
  • PNAME – Defaults to random 8 character value – Allows for specific pipe name to be chosen.
  • TIMEOUT – Defaults to 60 second – Used to change the wait time for the client to connect to the Implant, used in slow networks.
  • EXE – Generates a stand-alone executable;
  • CLIENT – Runs the script in client mode to connect to a deployed Executable;
  • TARGET – used to specify a remote IP Address.
  • Domain/User/Password/Hash – used to provide credentials for authentication.
  • Domain2/User2/Password2 – used to map a drive to the target system, when a hash is being used as the primary authentication mechanism.
  • Dir – used in EXE mode to output the generate executable.
  • Automation – used in EXE mode, directory location of the Automation DLL.

Interaction

There are 3 main functions that have been created to interact with the implant from a client. The first and probably the most useful, especially when we introduce templates, is Pbind-Command. This simply registers a command in a variable that is read in by the client and passed to the implant (server) before being executed. A simple example is shown below:

Pbind-module c:\folder\powerup.ps1The second is Pbind-Module, which allows you to read in any other ps1 file and have it injected into memory on the implanted host. Pbind-Command can then be used to execute any of the functions in the ps1 script. This has a limitation and does not work well within a C2 setup, because all scripts have to be local to the client. In most cases the client is already running on a target workstation and would require all scripts to be uploaded to the client before being sent on to the implant.

Pbind-Squirt was a designed to help resolve the limitations of Pbind-Module. The idea for this function was to embed a number of scripts as base64 objects into the script that can then be called and auto executed into memory on the client. The only one that has been embedded is PowerUp, to assist with asset review on newly implanted hosts.

However, in practice neither Pbind-module nor Pbind-squirt were optimal and instead a new solution was constructed, called ‘Templates’. Effectively this was just a better way to interact with the Pbind-Command function. It was decided that by creating a number of small scripts which can automate tasks, it is possible to carry out similar ideas to Pbind-module and Pbind-squirt. Tasks such uploading mimikatz and extracting passwords, uploading PowerView and running queries or uploading invoke-SMBExec and attacking other machines, can all be scripted using a similar template to the one below:

The best way to see how the script runs is to download the script and have a go. The screenshot below shows a simple example of running the script locally under the context of another user, while also executing commands.

Video Tutorial

We have created a video tutorial to help illustrate the use of Invoke-Pbind.

Download

github GitHub: https://github.com/nettitude/PoshC2/blob/master/Modules/Invoke-Pbind.ps1