Updog is a replacement for Python's SimpleHTTPServer. It allows uploading and downloading via HTTP/S, can set adhoc SSL certificates and use HTTP basic auth. It was created by sc0tfree and can be found on his GitHub page here. In this blog post we will use updog to exfiltrate information and show you the network indicators left behind from its usage.
The Attack
We are starting updog with all the default settings on the attacker machine, this means it will expose the directory we are currently running it from over HTTP on port 9090:
In order to quickly make updog publicly accessible over the internet, we will use a service called, Ngrok. This service exposes local servers behind NATs and firewalls to the public internet over secure tunnels - the free version of Ngrok creates a randomised URL and has a lifetime of 8 hours if you have not registered for a free account:
This now means that we can access our updog server over the internet using the randomly generated Ngrok URL, and upload a file from the victims machine:
The Detection using NetWitness Network
An item of interest for defenders should be the use of services such as Ngrok. They are commonly utilised in phishing campaigns as the generated URLs are randomised and short lived. With a recent update to the DynDNS parser from William Motley, we now tag many of these services in NetWitness under the Service Analysis meta key with the meta value, tunnel service:
Pivoting into this meta value, we can see there is some HTTP traffic to an Ngrok URL, an upload of a file called supersecret.txt, a suspicious sounding Server Application called werkzeug/1.0.0 python/3.8.1, and a Filename with a PNG image named, updog.png:
Reconstructing the sessions for this traffic, we can see the updog page as the attacker saw it, and we can also see the file that was uploaded by them:
NetWitness also gives us the ability to extract the file that was transferred to the updog server, so we can see exactly what was exfiltrated:
Detection Rules
The following table lists an application rule you can deploy to help with identifying these tools and behaviours:
Appliance | Description | Logic | Fidelity |
Packet Decoder | Detects the usage of Updog | server begins 'werkzeug ' && filename = 'updog.png ' | High |
Conclusion
As a defender, it is important to monitor traffic to services such as Ngrok as they can pose a significant security risk to your organisation, there are also multiple alternatives to Ngrok and traffic to those should be monitored as well. In order for the new meta value, tunnel service to start tagging these services, make sure to update your DynDNS Lua parser.
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