Users may find it difficult to host a PoshC2 server as it requires a Windows host, either directly connected to the Internet or in a position to be NAT’d through a firewall from an Internet facing C2 proxy. In this short post we’re going to show you how you can solve this problem in under 30 minutes with a $5 VPS.
For this to work you will need to create a small VPS from any provider. In this tutorial we’re going to use Digital Ocean, but feel free to use AWS, Azure, Vultr or one of the other providers out there.
First, start by creating a simple $5 per month Digital Ocean droplet, using Ubuntu 16.04 or similar. The reason we’re using Ubuntu 16.04 is their tutorial for OpenVPN has been developed on this version, and we want to keep it simple. Once you’ve created the droplet, it should look something like this in your Droplets tab:
The next thing we need to do is get the host updated with the latest security patches, so perform an apt-get update and upgrade.
When you’re all up-to-date, we’ll install Apache2 which will be used as both the native web server and the proxy with which to forward all PoshC2 communication traffic through to your Windows host. It is important to note we only want the communications traffic to be forwarded and no other URLs.
To start this off, install apache as per the instructions below and enable the modules to allow proxying with Apache.
apt-get install apache2
a2enmod ssl
a2enmod rewrite
a2enmod proxy
a2enmod proxy_http
a2enmod headers
service apache2 restart
Once the default Apache2 install has completed, we find it easier to completely delete all files in the ‘sites-enabled’ and ‘sites-available’ folders of
/etc/apache so that we can start from a fresh config, but this is purely an optional thing so do whatever best suits you and your setup. With one config file, we split out the virtual hosts and have both HTTP (port 80) and HTTPS (port 443) in one place.
The file we’re going to create for this postis called
proxy.conf and should be located in the sites-available folder –
/etc/apache2/sites-available/proxy.conf
The configuration should look something like the one below. Obviously yours may differ slightly if you decide to use multiple ports or have different virtual hosts with multiple names going through the same Apache server. However, to keep things simple, this is the default configuration without the rewrite rules applied.
Once you’re all done, restart your Apache2 service to ensure you have no errors.
service apache2 restart
The next thing you need to do is add your PoshC2 Apache Rewrite rules to the configuration. This is where it can get quite complex depending on what you want the rules to do. As an example, when performing a Red Team engagement, your C2 infrastructure should be sufficiently locked down and should only allow implants from the correct IP address range of the Customer.
To add whitelisting on the C2 proxy, create a file with all the IP addresses that are known to be the client. There is a slight nuance with Apache as you have to add the list like this (
/etc/apache/whitelist):
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10.0.0.1–
10.0.0.2–
Once you have the whitelist, you can use a function in the rewrite rules called
RewriteMap to add the IP address list, to then use in the rewrite conditions. Here is a simple Rewrite Rule which will take the list above – if this is not found it will not process the rewrite rule. You have to do this for each rewrite rule you want for each URL. In this case we are applying to the
/connect path as this is where the implant gets the stager, but if you customize the PoshC2 URLs then this may be different.
To complete the full Apache config, use the link below as a guide, but note you may need to change this for your PoshC2 setup as you customize the URLs for better evasion. Don’t forget that if you do change your URLs when setting up PoshC2 there is a file called
apache2.conf in the root directory which created the rewrite rules for you. This does not add a whitelist but you can do this using the above config.
Now we have the Apache2 web server with our rewrite rules, we need to connect our Windows host to the this VPS using OpenVPN. I’m not going to walk through the exact steps to setup OpenVPN as there is a really good step by step guide which should take no more than around 20-30 minutes to follow and setup:
Once you’ve followed the guide to setup OpenVPN on the host in TUN mode, you can drop your client config onto your windows host. The OpenVPN
server.conf configuration should look similar to this. This one is hosted over TCP 53 as we have 443 in use by the Apache Web Server.
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port53
proto tcp
dev tun
ca ca.crt
cert server.crt
key server.key
dh dh2048.pem
server10.10.10.0255.255.255.0
ifconfig-pool-persist ipp.txt
keepalive10120
comp-lzo
status openvpn-status.log
verb3
cipher AES-128-CBC
auth SHA256
key-direction1
Next, following the instruction in the Digital Ocean tutorial, create a client configuration file which matches the server settings and key files you setup and download this to your Windows host. Use the following link to install the Windows client, which should add a small icon to the task bar where you can import your configuration file to and connect.
At this point you should be nearly done. Once you get OpenVPN to successfully connect to the VPS, you can provide the Windows IP address in the Apache2 rewrite rules as the PoshC2 server and it will direct all traffic aimed for PoshC2 directly to the host. Remember that with this setup you will need to provide the external IP address or host name of the VPS as the PoshC2 server as shown in the image below – otherwise the payloads and droppers will be created with the wrong C2 server.
Having this kind of setup makes it extremely easy to deploy PoshC2 and should take no more than around 30 minutes of setup to have things fully weaponised and ready to go. Check out the latest updates for PoshC2 v3 from the blog below which induces a socks proxy (SharpSocks) to allow RDP via a HTTPS beacon.
https://labs.nettitude.com/wp-content/uploads/2018/01/word-image-1.png216762Ben Turnerhttps://labs.nettitude.com/wp-content/uploads/2016/07/NETT_LABS_LOGO-300x139.pngBen Turner2018-01-31 14:10:052018-07-26 15:02:13Making PoshC2 More Accessible With a $5 VPS
We’ve been working on quite a few changes since the release of PoshC2 v2, our public Command & Control framework, back in December 2016. In this blog we’ll talk about the top changes and feature improvements. If you want to view all the changes, we’ve now added a CHANGELOG.md to the repository.
Daisy implant now supports multi layered pivoting (no limit on hops)
Domain fronting for C2 comms
C++ reflective DLL, utilising UnmanagedPowershell and PoshC2’s Custom EXE
Shellcode generator, utilising @monoxgas‘s new sRDI tool we can generate shellcode on the fly from the Reflective DLL created in C++
Stable migration utilising Inject-Shellcode which uses our newly created shellcode
New AutoRuns that allow the user to create commands that run when a new implant is initiated
Pre/Post Implant Help – The Implant-Handler window now has a pre and post help menu which allows you to do various tasks when you have no implant, such as autoruns
One of the most important tools for a red teamer is the SOCKS Proxy. This enables the creation of a tunnel between two machines such that any network traffic forwarded through it appears to have originated from the machine at the end of it. Once a foothold has been gained on a machine, a SOCKS proxy can be deployed between the operators machines and the target in order to access subnets, machines and services that would not normally be directly accessible. This includes being able to RDP to another machine or even to browse the corporate intranet.
SOCKS support is built into most modern browsers and cURL. However, to use tools like rdesktop or nmap, proxychains on Linux can be used to tunnel the traffic. In order to simulate ProxyChains when using Windows, software such as ProxyCap (http://www.proxycap.com/) can be used.
Previously, if tools like PoshC2 or Empire were used to gain a foothold and SOCKS is required then another implant, such as Meterpreter, would have to be deployed in order to provide the ability to tunnel TCP traffic into the internal network. We arrived at the decision that deploying a full implant just for SOCKS support is overkill and while e.g. Meterpreter is very good, it is also can be noisy and is not an appropriate representation of most sophisticated threat actors TTPs. Since PoshC2 is our publicly available C2, we wanted to add this ability for the wider world too, just like we have in our internal tooling.
When started, the implant will connect back via an HTTP request to the specified host. This is known as the command channel. By default (and this timing can be changed via the
--beacon flag in the implant) the server will be contacted every 5 seconds to check if there are any connections that need to be opened or closed on the implant side. Once the command channel has successfully connected for the first time, the SOCKS listener port is opened on the server; this port is what proxychains or proxycap should be configured to connect to.
Once this has started you can then start your web browser or RDP etc. and connect to the internal network. Every time the browser etc. opens a connection to the SOCKS port, a job is queued for the command channel and the implant on the default 5 second timer will connect up check to see if there any new connections that need to be made or closed. If one does need to be opened, this will be then be assigned its own session identifier and traffic will flow and be tunnelled over HTTP/S on separate requests.
A typical usage scenario is shown in the diagram above. A foothold has been gained on a machine with internet access, but only via HTTP/S, and RDP needs to be used to access the RDP Host (credentials for this box have, of course, been obtained). The SharpSocks server is started and so is the implant. Proxychains is then configured by the operator to point to the SOCKS port. Rdesktop is then started and traffic is tunnelled via HTTPS to the implant host, where the connection is then made to the RDP host.
Design Goals
The project originated as a way to provide SOCKS proxy functionality to Nettitude’s PoshC2 project. The design goals were as follows:
Ability to operate as part of another implant or its own separate instance
Communication over HTTP/S
Minimal CPU/memory load on implanted machine
Encrypted transport
Configurable locations within a HTTP request for the payload
Proxy aware
IPv6 support
Ease of integration into other projects
Easing overriding functionality by a consumer such as encryption or transport method
Usage
The best usage experience for this currently is via PoshC2.
SharpSocks, written by Rob Maslen (@rbmaslen), utilises a C# AssemblyLoad to run a socks4a proxy on the implant, calling back to a server which can be either located on the same PoshC2 instance or on a different host. The most convenient way to deploy this is via the same PoshC2 host, but on a separate port. The comms can be split via the Apache Rewrite rules if you’re using a C2 proxy on the Internet. It may also be a good idea to use a separate host for this traffic as you may have to speed up comms to 1 or 2 second beacons and therefore utilise a separate proxy host, but they can all point back to the same PoshC2 instance in the back end.
The comms URLs for both PoshC2 and SharpSocks can now be fully customised when first setting the server up. These can then be added to an
apache.conf file located in the root of the PoshC2 folder.
To deploy SharpSocks all you need to do is run the following command from within a live implant. This will create a new encryption key and subsequent channel and start both the implant and SharpSocks server for you:
The next few sections walk you through using SharpSocks in a standalone manner.
There are two Visual Studio Solutions which build both the server and the implant. These are both built initially as DLL’s, however the solutions also contain projects for executables that wrap the DLLs and allow for testing of the functionality. These exe’s are not designed to be deployed in a production scenario.
The DLLs are designed to be either launched via the test executables or via the helper functions within the DLLs themselves, enabling other usage via other projects/languages. Also included within the binaries directory is also the PowerShell script that is used by PoshC2.
Server App (SharpSocksServerTestApp)
Running the server binary with the
--help flag, the following options are listed. In order to launch, the only value that is required is the encryption key. This should be supplied in Base64; the default algorithm is AES-256.
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-c,--cmd-id=VALUE Command Channel Identifier,needs tobe shared with the server,defaultis7f404221-9f30-470b-b05d-e1a922be3ff6.
This will start the HTTPS server (HTTPS requires that a certificate is installed via netsh) listening on https://c2proxy.on.the.internet. The communications are encrypted via the key NqeEk7h4pe7cJ6YGB/4q3jHZ5kp64xsghwNwjYUFD0g=, the command channel is identified by bc448036-f957-45d9-b0e7-997b4121034f. The session identifier would be transmitted via the ASP.NET_SessionId cookie and smaller payloads via the __RequestVerificationToken cookie.
Server DLL (SharpSocksServerDLL)
Within the SharpSocksServer.dll is a class called
SharpSocksServer.Source.Integration.PSSocksServer which contains a single method called
CreateSocksController. This method is designed as a static helper to easily enable the creation and starting of the SharpSocksServer. In order to be used, the DLL/Assembly will first need to be loaded the
CreateSocksController method called and then the Start method called on the value returned. For usage of this it’s best to look in the PowerShell script included with this project.
Implant Test App (SharpSocksImplantTestApp)
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--use-proxy Useproxy server(forsystem proxy set thisandleave-mblank)
-m,--proxy=Proxy Url informat http://<server>:<port> (-p is implied)
This will start the implant which will attempt to connect to https://c2proxy.on.the.internet using the system proxy settings. The communications are encrypted via the key NqeEk7h4pe7cJ6YGB/4q3jHZ5kp64xsghwNwjYUFD0g=, the command channel is identified by bc448036-f957-45d9-b0e7-997b4121034f. The session identifier would be transmitted via the ASP.NET_SessionId cookie and smaller payloads via the __RequestVerificationToken cookie. The command channel will attempt to connect every 7.5 seconds to the SharpSocks server.
Implant DLL (SharpSocksImplant.dll)
Within the SharpSocksImplant.dll is a class called
SocksProxy.Classes.Integration.PoshCreateProxy which contains a single method called CreateSocksController. This method is designed as a static helper to easily enable the creation and starting of the implant. In order to be used, the DLL/Assembly will first need to be loaded the CreateSocksController method called and then the Start method called on the value returned. As with the SharpSocks Server, as an example of usage of this it’s best to look in the PowerShell script included with this project.
DAISYIMPLANT – PIVOTING IN POSHC2
To enable multi-layered pivoting in PoshC2 we have created a module called Invoke-DaisyChain. This must be run as an administrator on a compromised host within the compromised network. This will essentially create an HTTP proxy server running on the host to transport PoshC2 comms traffic from the internal network out to the PoshC2 instance instead of going direct with CreateProxyPayload.
To start the DaisyChain server, simply run this command with your C2 configuration. Proxy settings are optional as is the domain fronting URL:
This will create a variety of payloads that are specific to this pivot server. Therefore, if you run the new payloads (called ‘jason’ in this instance) it would attempt to connect to the proxy port running on this host, rather than going direct to the Internet. To execute these payloads remotely, you can use any of the lateral execution methods built into PoshC2 or any of your custom lateral movement methods.
There is no limit on the number of times you can pivot into a network. However, if any of the machines in the chain get restarted for any reason, the entire chain will die. This is worth noting when performing pivoting within a network using Daisy Chaining.
DOMAIN FRONTING FOR C2 COMMS
PoshC2 can now use domain fronting for comms. There is a caveat to this; the host must have .NET v4.0.30319 installed and usable to the PowerShell instance. However, if the host does not have this version of the CLR installed it will default back to the underlying CDN hostname, for example cloudfront.net or azureedge.net. The way we perform domain fronting in PoshC2 is by adding the Host header to the web requests.
This is a much stealthier option for comms as you can utilise hostnames with better reputation without needing to buy new domains and obtain reputation yourself. There are many examples of these on the Internet, but as a proof of concept this example uses ‘d0.awsstatic.com’.
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$wc=New-ObjectSystem.Net.WebClient;
$wc.Headers.Add("Host",”example.cloudfront.net”)
$wc.DownloadString(“d0.awsstatic.com”)
PRE-IMPLANT HELP MENU
The new pre-implant help menu allows you to configure various auto-runs, double check the server configuration and make and significant changes to the C2 server. It also allows you to test your configuration by issuing PwnSelf to obtain an implant.
Other commands that can be altered are C2 default beacon time, Clockwork SMS API key and mobile number for text message alerts of new implants.
AUTO-RUNS
We have now implemented the concept of Auto-Runs. This allows the user of PoshC2 to automate various tasks when an implant first comes in. A few use cases of this could be:
auto migrate from PowerShell
capturing a screenshot for situational awareness
install persistence
Essentially, any command that can be issued within PoshC2 can be turned into an Auto-Run.
This menu can be found on the pre-implant help menu. An example of this menu has been shown below:
AUTOMIGRATE-FROMPOWERSHELL (AM)
The auto migrate from PowerShell feature has been added and by default will start another process in netsh.exe unless otherwise stated by the ‘-newprocess’ parameter. This utilises unmanaged PowerShell via the C++ Reflective DLL.
C++ REFLECTIVE DLL
The C++ Reflective Dll utilises the concept from the unmanaged PowerShell code by @tifkin_.
We have created a .NET binary that is loaded by creating an instance of the CLR (v2.0.50727 or v4.0.30319) in runtime and patching the implant over the top when creating a new payload. This is done by creating a blank variable in the C++ code and overwriting the code where 5000 A’s exist. Once compiled we find the location of this code and add the offset to the PatchDLL function as shown below.
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if($Arch-eq'x86'){
$dllOffset=0x00012D80
}
if($Arch-eq'x64'){
$dllOffset=0x00017100
}
In addition, PoshC2 converts the newly created reflective DLL into Shellcode via @monoxgas’s sRDI PowerShell module. This module converts Reflective DLLs into position independent shellcode.
The Reflective DLL and new Shellcode has enabled PoshC2 to be more flexible in its execution and deployment. Many other tools will allow for a reflective DLL or shellcode to be loaded. Take for example, the MS17-010 eternal blue exploit written in Powershell. This exploit takes shellcode as a parameter to execute if the host is successfully exploited; having Shellcode as a payload format allows this to be possible.
Also for migration, we now use either the reflective DLL or the Shellcode to squirt the implant into another process. When first starting PoshC2 it will create both the reflective DLL’s as shown below.
Posh_x64.dll
Posh_x86.dll
To test these out, they can be called via rundll32:
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Rundll32 Posh_x64.dll,VoidFunc
Rundll32 Posh_x86.dll,VoidFunc
Posh-shellcode_x64.bin
Posh-shellcode_x86.bin
To test these out, they can be called via the new Inject-Shellcode script or by using ‘migrate’ in the implant window:
@rbmaslen has created a super fast portscanner written in C# which has been ported to PoshC2 using the AssemblyLoad function rather than AddType. This is not to obfuscate the code at all, but in case you’re not aware the add-type function in PowerShell actually compiles the code on the fly and touches disk in the interim. This is why both the SharpSocks and Portscanner modules have been written to use AssemblyLoad instead.
The port scanner can take various parameters, but mostly we like the fact you can go into ‘super fast’ mode which allows you to set the maximum queries per second (-maxQueriesPS). This is similar to masscan’s rate parameter. This is good when your intention is not to be stealthy and you want to perform quick port scanning against a target. An example has been shown below.
On the other hand, when performing Red Teaming the ultimate aim is usually to be stealthy and we have implemented the option for delaying the portscan. For example, if you set the max queries per second (-maxQueriesPS) to 1 and the delay (-Delay) to 10, it will attempt to connect to each port with a 10 second delay hopefully bypassing any host or network IDS detection. An example of this has been shown below.
CONCLUSION
Go and download the latest version of PoshC2 with SharpSocks and let us know what you think!
https://labs.nettitude.com/wp-content/uploads/2017/11/SharpSocks.gif9891890Rob Maslen and Ben Turnerhttps://labs.nettitude.com/wp-content/uploads/2016/07/NETT_LABS_LOGO-300x139.pngRob Maslen and Ben Turner2017-11-15 14:43:342018-07-26 15:02:18PoshC2 v3 with SOCKS Proxy (SharpSocks)
There have been a few cool updates to PoshC2, our public Command & Control (C2) software, since we first released it. In this post, we’ll walk you through some of these new features so that you can try them out for yourself. We encourage you to give it a go and get involved. Read more →
https://labs.nettitude.com/wp-content/uploads/2016/06/PoshC2-Server.png7611220Nettitude Labshttps://labs.nettitude.com/wp-content/uploads/2016/07/NETT_LABS_LOGO-300x139.pngNettitude Labs2016-12-01 14:48:552018-07-26 15:02:25PoshC2 - new features
PoshC2 is a proxy aware command and control framework written completely in PowerShell. It is designed to aid penetration testers with red teaming, post-exploitation and lateral movement. Read more →
https://labs.nettitude.com/wp-content/uploads/2016/07/poshc2-ih.png634926Ben Turnerhttps://labs.nettitude.com/wp-content/uploads/2016/07/NETT_LABS_LOGO-300x139.pngBen Turner2016-07-12 14:04:512018-07-26 15:02:31Nettitude Labs release PoshC2, a command and control framework
