In Part 1 of the series we looked at how an AWS Lambda-powered feature was exploited in a web app penetration test initially leading to RCE and further on with out-of-band data exfiltration via DNS. Though the exact mechanism of achieving remote-code execution with Python was not discussed, we went in depth in how to return data as a result of the code being executed. Initially, with ascii-to-integer encoding I was able to find the username of the runtime user – sbx_userNNN.

This is a war story of an AWS web application test where remote code execution was first obtained on the client’s application. Then I needed to write my own DNS tunnelling ‘protocol’ to get the data out. Following a number of twists and turns I impersonated the application and attempted to laterally move within the AWS tenant.

Before storytelling though, let’s start with a public service announcement: