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HTB CTF - I know Mag1k

caffiendkitten profile image DaNeil C Updated on ・3 min read
  • CTF Name: I know Mag1k
  • Resource: Hack The Box CTF
  • Difficulty: [50 pts] medium range

Note::: NO, I won't be posting my found FLAGS, but I will be posting the methods I used.


Flag1

  • Hint: Can you get to the profile page of the admin?
  • Acquired By:
    1. When first looking at the site it appears to be a simple login page.Alt Text If I look at the code there is nothing special is the code itself or the cookies.
    2. Now I want to look at the network traffic, and again, nothing stands out to me. Alt Text
    3. Now I want to register and see if it will let me register. Again, there is nothing special in the code, network, or storage of the site currently. First thing I do it attempt to login at admin but it tells me my username/password is wrong. So I try registering as admin and it lets me. Interesting.
    4. Now that I have an account with a username of "admin" and I am logged in I see that I have a new cookie.Alt Text This cookie is obviously URL encoded and base64. This is obvious because of the "%3D" and that there are two of those at the end of the cookie. "%3D" becomes an "=" and having two at the end of a string is common base64 encoding so I want to try and decode it. For this I will be using BurpSuite's Decoder because I like that it lets me chain decoding easily. Sadly, this did not produce anything obvious. Alt Text
    5. This CTF is talking about magic and after some research into encryption padding I see there is a thing called "Oracle Padding Attack" and I believe this is it. The oracle padding attack utilizes the blocks of each bytes to decrypt the results of encryption and I need to work with padBuster to solve this. To use padBuster I will run perl padBuster.pl http://docker.hackthebox.eu:xxxxx/profile.php F%2BRHLTZ80qRhaTpGGnvdimT0Dob9Qrgk4IkCNgBQYgDlmEc99emZPA%3D%3D 8 --cookies iknowmag1k=F%2BRHLTZ80qRhaTpGGnvdimT0Dob9Qrgk4IkCNgBQYgDlmEc99emZPA%3D%3D to have it sycle over it and break it. Alt Text Once it completed I got an output that revealed the formatting of the cookies data. Alt Text
    6. Now that I know the layout I can see that I have a role that I need to change to "admin". To do this we will use padBuster again and add in the plaintext of the formatting of the new cookie we want. perl padbuster.pl http://docker.hackthebox.eu:30769/profile.php F%2BRHLTZ80qRhaTpGGnvdimT0Dob9Qrgk4IkCNgBQYgDlmEc99emZPA%3D%3D 8 --cookie "iknowmag1k=F%2BRHLTZ80qRhaTpGGnvdimT0Dob9Qrgk4IkCNgBQYgDlmEc99emZPA%3D%3D" -plaintext "{\"user\":\"admin\",\"role\":\"admin\"}" This produced a new cookie with me as the role "admin". Alt Text
    7. Now that I have a new cookie I am able to copy it and paste it into the browser and now when I refresh the page I am an admin and the flag is right there.Alt Text

Learned

This CTF taught me about the padBuster tool the most.
I am using this as a shooting off point to learn more about padding and cipher block chaining that I will write about later.


Happy Hacking

Resources:

  1. https://robertheaton.com/2013/07/29/padding-oracle-attack/
Please Note: that I am still learning and if something that I have stated is incorrect please let me know. I would love to learn more about what I may not understand fully.

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