How i completed MongoDB's Challenge | December 1, 2022 at 4:35 PM GMT+115>
At work today, MongoDB had a presentation on securing their product, Atlas. At the end of this presentation they issued us a challenge, the presentation itself contains a "payload". The challenge for us is to extract this payload and retrieve the credentials within. A note on these credentials, they are dummy credentials created for the challenge, and do not actually work on anything.
The Challenge Pt. 2
This file was shared through Sharepoint. An issue with using sharepoint is if you open the file using Powerpoint online and save a copy, this is essentially the same as "Save As", meaning the file is saved as it exists in powerpoint's memory. This is an issue because the payload exists in a file that's not a part of the powerpoint file's spec, and as such, it gets removed. Instead of opening and saving a copy, you need to download a copy. This can be done by clicking the 3 dots next to the file in your search for file browser in sharepoint.
All office documents are actually zip files in disguise, so the first thing i tried, was to unzip the document. This revealed a whole list of .xml files, my next challenge was to locate any files that seem out of place. I spent about 30 minutes looking through the files and found a file called `_rels_ver.xml`. This file did not look too out of place on it's own but the contents was a bit of a red flag for me. There were two elements that looked to contain base64 encoded data, one was a short string, the other was a large blob.
Decoding the short string revealed a cheeky message, "very close!", but decoding the long one revealed only garbled data. The output from the big blob of base64 encoded text looked like binary data, but it did not start with 'ELF', a key indicator that the data is an executable for linux. So i tried a few decompression methods instead as They can look similar when represented by text. Turns out it was a gzip compressed string of text containing the payload we were looking for! Just for clarification though, this payload was dummy data that was created for the purpose of this challenge, it's not real data.
It was a fun challenge. Thanks to CyberChef for the assistance decoding that large blob of text, while it would not be imposible to decode in a terminal, it was quite simple to drag and drop various modules in and out to test.