RailsGoat Security CTF

A long time ago in a galaxy far, far away . . .

RailsGoat is a vulnerable version of the Ruby on Rails Framework from versions 3 to 5. It includes vulnerabilities from the OWASP Top 10, as well as some "extras" that the initial project contributors felt worthwhile to share. This project is designed to educate both developers, as well as security professionals.

Introduction

Welcome to FinanceIt's in-house security training module, built on top of the RailsGoat project and made in the style of a Capture the Flag event, a common type of competition in the information security world, similar to a hack-a-thon or coding contest.

There are typically two types of CTFs: Attack/Defend and Jeopardy style. Our training module is modeled after an Attack-based CTF and places you in the role of a black hat hacker aiming to exploit a vulnerable web application.

Each attacker will be required to find a series of “flags” which are hidden throughout the RailsGoat app. Finding all the flags will require the attacker to exploit common web vulnerabilities based on the OWASP Top 10 Web Security Risks.

The flags are ordered in rough order of increasing difficulty with resources and reading material on various web vulnerabilities provided throughout. Each flag appears in the form: CTF[NameOfFlagHere].

CTF Instructions

Level One: Noob Town

Theme: Sensitive Data Exposure
Hint: Look around the app for any suspicious information lying around. Remember that only suspicious people would dare to take Paid Time Off (PTO).
Solution: Navigate to the bottom of the PTO tab.
Password: CTF[DemonSlayer]

Level Two: Toddler with an iPad

Theme: Sensitive Data Exposure
Hint: Look for suspicious CSS classes. The Work Info tab seems to be particularly stylish.
Solution: Use Inspector to find the hidden CSS class of the SSN column in the Work Info tab.
Password: CTF[OnePiece]

Level Three: Chrome Inspector Master

Theme: Security Misconfiguration
Hint: If configured incorrectly, an application will display a full routing trace instead of a 404 page.
Solution: Go to a non-existent path and look for a flag in the list of routes.
Password: CTF[JojosBizarreAdventure]

Level Four: Security Engineer at SolarWinds

Theme: Security Misconfiguration
Hint: Look for privileged routes that aren't properly protected.
Solution: Navigate to /admin/1/get_all_users and look for a user with an exposed Secure UUID.
Password: CTF[ChainsawMan]

Level Five: Dollar Store Neo

Theme: User Access Control
Hint: There is an admin-level page that is missing proper access controls.
Solution: Go to /admin/1/dashboard from any non-admin user.
Password: CTF[CowboyBebop]

Level Six: NSA Watchlist

Theme: Insecure Direct Object Reference
Hint: There is a file secret_token.rb which contains sensitive information. On another note, it seems files can be downloaded from the Benefit Forms tab.
Solution: Use the link for downloading files in the Benefit Forms tab and replace the file name with secret_token.rb.
Password: CTF[FullmetalAlchemist]

Level Seven: Greensky Corporate Spy

Theme: Unvalidated Redirects and Forwards
Hint: Log out and try redirecting a user to Financeit's website.
Solution: Go to /login?url=https://financeit.io and login as a valid user.
Password: CTF[FromTheNewWorld]

Level Eight: Gandalf the Grey-Hat Hacker

Theme: DOM or Python XSS (Cross-Site Scripting)
Hint: You can execute remote commands by browsing to /#test=<script>...</script>.
Solution: Go to /#test=<script>alert(document.cookie)</script>.
Password: CTF[Baccano]

Level Nine: Gandalf the White-Hat Hacker

Theme: Stored XSS (Cross-Site Scripting)
Hint: When creating new objects in the DB, you can store JS as an attribute which will be executed whenever it's called.
Solution: Sign up with a new user with a First Name of <script>alert(document.cookie)</script>.
Password: CTF[CodeGeass]

Level Ten: Gandalf the Black-Hat Hacker

Theme: Reflected XSS (Cross-Site Scripting)
Hint: Uploading files can be used to inject a JS alert. The document's cookie is a good place to start.
Solution: Upload a file named ><img src=1 onerror=alert(document.cookie)> to the Benefit Forms tab.
Password: CTF[MobPsycho100]

Level Eleven: NSA Most Wanted

Theme: Cross-Site Request Forgery (CSRF)
Tools: Code Editor
Hint: The Pay model has a hidden attribute called show_secure_token which is automatically false if created through the Pay tab.
Solution: Open a script HTML file to create a Pay object with show_secure_token set to true.
Password: CTF[HunterXHunter]

Level Twelve: Cyberpunk 2078

Theme: Missing Function Level Access Control
Tools: Chrome Inspector or Burpsuite
Hint: Send a tampered message masquerading as another user. View the message.
Solution: Send a message normally and intercept the POST request. Modify the creator_id to another user and send the request.
Password: CTF[LegendOfTheGalacticHeroes]

Level Thirteen: Destin's Reincarnation

Theme: SQL Injection / Privilege Escalation
Tools: Chrome Inspector
Hint: Use the password change function to change the admin's password. Browse for the flag on privileged pages.
Solution: Intercept a password change POST and modify the user_id with 999') OR admin = 't' --'"). Navigate to Analytics tab.
Example:

"utf8=%E2%9C%93&_method=patch&authenticity_token=Bbl9ldbL6dgWq6YLPwQjxhHKVNrKwi13FiFOEhb%2BIcp0FdjR2VlxDHpl6WUTb7KSUnBk4WbdICMWtBmROxQBIw%3D%3D&user%5Buser_id%5D=999%27)%20OR%20admin%20%3D%20%27t%27%20--%27%22)&user%5Bpassword%5D=demonslayer&user%5Bpassword_confirmation%5D=demonslayer"

Password: CTF[DrStone]

Level Fourteen: Power Level Integer Overflow

Theme: Broken Session Management / Privilege Escalation
Tools: Burpsuite
Hint: This application re-uses encryption keys for auth tokens. The admin has a user_id of 1.
Solution: Create a Pay object with all attributes set to 1. Modify the encrypted key to be url-encoded and intercept a GET request with Burpsuite. Navigate to Dashboard tab as admin.
Example: Cookie: auth_token=YuiYZyqVrlsLk7%2b6YcrC1Q%3d%3d
Password: CTF[SteinsGate]

Level Fifteen: Ne Plus Ultra

Theme: Command Injection
Tools: Burpsuite
Hint: Find a way to create a directory called mischiefmanaged on the server.
Solution: Intercept an upload/download request, modify the benefits[backup] to true, and append ;+mkdir+mischiefmanaged to the filename. Navigate to Benefit Forms tab.
Password: CTF[GraveOfTheFireflies]

Bonus Level: Oscar-Winning Performance

Theme: High Performance Computing
Tools: Code Editor, Terminal
Hint: Every function in the code actually just performs a simple arithmetic operation, but done in a very roundabout way. Try distilling each function into an equation to uncover the full behaviour of the app.
Password: HV15-mHPC-067e-751e-f50e-17e3

The goal of this challenge is simply to run the file oscar-winning-performance.cpp to completion, the flag should be printed out at the end of the program. As this is a .CPP file written in C++, you will first need to compile the file before running it:

> g++ -o runthis oscar-winning-performance.cpp
> ./runthis

Notice that the file takes a very long time to complete and seems to run endlessly. Therefore, in order to reveal the flag, you simply need to refactor the program to improve performance without affecting its behaviour. The flag printed out at the end will begin with HV15.

Solution:

Begin by noting that every one of the helper functions actually performs a simple arithmetic operation, and so a mapping can be formed from the helpers to their mathematical values:

foo(a)        ==  a++
bar(a)        ==  a--
baz(a,b)      ==  a+b
spam(a,b)     ==  a-b
eggs(a,b)     ==  a*b
merry(a,b)    ==  a/b
xmas(a,b)     ==  a - (a/b)*b
hackvent(a,b) ==  b^a

Further note that the original code strictly uses uint64_t which are unsigned 64-bit integers, meaning there is no need to account for negative values when optimizing each helper function.

The key line in the original code is the following:

val = xmas(eggs(baz(hackvent(merry(i,42),3),val),i),0x42DEADBABEC0FFEE);

With the new mapping, this can be translated to mean:

val = xmas(eggs(baz(hackvent(merry(i, 42), 3), val), i), 0x42DEADBABEC0FFEE);
val = xmas(eggs(baz(hackvent(i / 42, 3), val), i), 0x42DEADBABEC0FFEE);
val = xmas(eggs(baz(3 ^ (i / 42), val), i), 0x42DEADBABEC0FFEE);
val = xmas(eggs((3 ^ (i / 42)) + val, i), 0x42DEADBABEC0FFEE);
val = xmas(((3 ^ (i / 42)) + val) * i, 0x42DEADBABEC0FFEE);
val = (((3 ^ (i / 42)) + val) * i) - ((((3 ^ (i / 42)) + val) * i) / 0x42DEADBABEC0FFEE) * 0x42DEADBABEC0FFEE

Re-writing the code to perform this equation in a more performant manner should yield a script similar to:

#include <stdio.h>
#include <stdint.h>

uint64_t hackvent(uint64_t base, uint64_t exp){
	if (exp==0) 
		return 1

	uint64_t x = mypow(base,exp/2);

	if(exp % 2==0) 
		return x*x;
	else 
		return base*x*x;
}

uint64_t xmas(uint64_t a, uint64_t b) {
	return a - (a/b)*b;
}

int main() {
	uint64_t val=0;
	for(uint64_t i=0; i<0xC0DE42; i++) {
                val = xmas((hackvent(3, i / 42) + val) * i ,0x42DEADBABEC0FFEE);
	}

	printf("HV15-mHPC-%04llx-%04llx-%04llx-%04llx\n",
		val>>48,(val&0x0000FFFF00000000)>>32,
		(val&0x00000000FFFF0000)>>16, (val&0x000000000000FFFF));
	return 0;
}

This newer script runs much faster and at the end of its execution, it outputs the following flag: HV15-mHPC-067e-751e-f50e-17e3.

Credits: Problem and Solution from Hackvent 2015.

Bonus Level: Something Fourier This Way Comes

Theme: Steganography
Tools: Code Editor, Image Processing Library (MATLAB, ImageMagick, etc.)
Hint: Try distilling the image by even or odd RGB values.
Password: f0urier-ru1ez

The goal of this challenge is to find a password hidden somewhere in the ballomatic.png image. Note that while this challenge is based on steganography, it does not require the use of any of the usual suspects in such challenges (binwalk, exiftool, xxd, etc.).

Part-way through this challenge, you will need to be aware of Fourier Transforms and specifically it's use in image processing: (https://www.cs.unm.edu/~brayer/vision/fourier.html).

Also relevant is knowledge of a long-running webcomic series known as XKCD: https://xkcd.com/2540/

Solution:

Filter the image by even RGB bits using the following script (or a similar tool):

from PIL import Image

img = Image.open('ballomatic.png')
pixels_orig = img.load()
(w,h)=img.size

outimg = Image.new( 'RGB', (w,h), "white")
pixels_out = outimg.load()

for i in range(0,h):
    for j in range(0,w):
      (r,g,b) = pixels_orig[j,i]
      if(r%2==0):
          pixels_out[j,i]=(0,0,0)

outimg.save("even-pixels-red.png","png")

This script can be run through the following:

> python3 -m pip install --upgrade Pillow
> python3 script_name.py

Note that the r%2==0 line means the script is filtering out the even red pixels. Alternatively, replace it with b%2==0 to filter out even blue pixels and similar for green pixels.

Filtering by red pixels results in a new image with a message saying that the princess is in another castle. Filtering by the blue pixels results in a new image with a message referring to XKCD #26: https://xkcd.com/26

This XKCD comic is about Fourier Transforms, so process the original ballomatic.png image using Fourier Transformations. You can also use an online tool like (https://ejectamenta.com/imaging-experiments/fourifier/).

The resulting image has the flag of f0urier-ru1ez.

Credits: Problem and Solution from Hackvent 2015.

Bonus Level: SHA-1-shank Redemption

Theme: Cryptography
Tools: Code Editor
Hint: Try a simple brute-force approach to finding the full lower-case flag, and then the case-sensitive flag.
Password: HV15-GnUj-1YQ7-vdYC-2wlr-E6xj

The flag for this round is similar to the following: HV15-G?UJ-1YQ7-?DYC-2WLR-E6?J. As you can see, there are three missing characters, where a ? appears instead of an alpha-numeric character. The following three bits of information are also available to you:

A valid flag contains both upper and lower-case characters, which means the above string is not currently in it's correct case as it contains exclusively upper-case lettering.
The following is an SHA-1 hash of the lower-case version of the flag: B39ECFBC2C64ADBB7C7A9292EEE31794D28FE224
The following is an SHA-1 hash of the actual case-sensitive flag: 0D353038908AD0FC8C51A5312BB3E2FEE1CDDF83

For this challenge, you must decrypt HV15-G?UJ-1YQ7-?DYC-2WLR-E6?J using knowledge of the SHA-1 cryptographic function and the above context clues.

Solution:

Use a simple brute-force approach to first find all the characters, by ignoring the case requirements and searching strictly for the lower-case version of the flag:

import itertools
import hashlib

target_lc='B39ECFBC2C64ADBB7C7A9292EEE31794D28FE224'.lower()
charset='abcdefghijklmnopqrstuvwxyz0123456789'

for i in itertools.product(charset, repeat=3):
    nugget = 'hv15-g'+i[0]+'uj-1yq7-'+i[1]+'dyc-2wlr-e6'+i[2]+'j'  
    h = hashlib.sha1()
    h.update(nugget)   
    h_hex = h.hexdigest()
    if h_hex == target_lc:
        print 'Lower-Case Flag: ' + nugget +' (sha1 '+h.hexdigest()+')'
        break

Then write a similar script to find the correct casing of each character using another brute-force approach:

import itertools
import hashlib

def all_casings(input_string):
    if not input_string:
        yield ""
    else:
        first = input_string[:1]
        if first.lower() == first.upper():
            for sub_casing in all_casings(input_string[1:]):
                yield first + sub_casing
        else:
            for sub_casing in all_casings(input_string[1:]):
                yield first.lower() + sub_casing
                yield first.upper() + sub_casing

target_cs='0D353038908AD0FC8C51A5312BB3E2FEE1CDDF83'.lower()

for i in all_casings(nugget):
    h = hashlib.sha1()
    h.update(i)   
    h_hex = h.hexdigest()
    if h_hex == target_cs:
        print 'Case Sensitive Flag: ' + i + ' (sha1 '+h.hexdigest()+')'
        break

The resulting scripts output the following:

Lower-Case Flag: hv15-gnuj-1yq7-vdyc-2wlr-e6xj (sha1 b39ecfbc2c64adbb7c7a9292eee31794d28fe224)
Case Sensitive Flag: HV15-GnUj-1YQ7-vdYC-2wlr-E6xj (sha1 0d353038908ad0fc8c51a5312bb3e2fee1cddf83)

Credits: Problem and Solution from Hackvent 2015.

Bibliography

This CTF project is a modified version of the open-source RailsGoat project set up by the OWASP Foundation. Original Source: https://github.com/OWASP/railsgoat
The challenge in Bonus Level: Oscar-Winning Performance is originally from HackVent 2015.
The challenge in Bonus Level: Something Fourier This Way Comes is originally from HackVent 2015.
The challenge in Bonus Level: SHA-1-shank Redemption is originally from HackVent 2015.

Extra Training

For a more involved coding, exercise, every participant is welcome to and encouraged to set up the original RailsGoat application here: https://github.com/OWASP/railsgoat

The original application is not a CTF, but contains many of the same vulnerabilities as well as tests which are failing to start with. For extra training, please modify the code itself to try and patch the different vulnerabilities across the application; each test should go from failing to pending as each exploit is patched.

Setting Up CTF Locally

To begin, if you do not have Ruby, Git, MySQL, and Postgres, we suggest using this site to install the software. Pick the appropriate operating system and follow the instructions.

After installing the above software, clone this repo:

$ git clone git@github.com:OWASP/railsgoat.git

NOTE: NOT NECESSARY IF YOU WANT TO WORK WITH RAILS 6. Otherwise, if you wish to use the Rails 3 or 4 versions, you'll need to switch branches:

$ cd railsgoat
$ git checkout rails_3_2
$ git checkout rails_4_2

Navigate into the directory (already there if you followed the previous step) and install the dependencies:

$ bundle install

If you receive an error, make sure you have bundler installed:

$ gem install bundler

Initialize the database:

$ rails db:setup

Start the Thin web server:

$ rails server

License

The MIT License (MIT)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Name		Name	Last commit message	Last commit date
Latest commit History 1,226 Commits
app		app
config		config
db		db
doc		doc
gauntlt_scripts		gauntlt_scripts
lib		lib
log		log
public		public
script		script
spec		spec
test		test
vendor/assets		vendor/assets
.cane		.cane
.gitignore		.gitignore
.overcommit.yml		.overcommit.yml
.powrc		.powrc
.rspec		.rspec
.ruby-gemset		.ruby-gemset
.ruby-version		.ruby-version
.travis.yml		.travis.yml
Dockerfile		Dockerfile
Gemfile		Gemfile
Gemfile.lock		Gemfile.lock
Guardfile		Guardfile
LICENSE.md		LICENSE.md
Procfile		Procfile
README.md		README.md
Rakefile		Rakefile
Vagrantfile		Vagrantfile
Vagrantfile.proxy		Vagrantfile.proxy
config.ru		config.ru
docker-compose.yml		docker-compose.yml

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RailsGoat Security CTF

A long time ago in a galaxy far, far away . . .

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A long time ago in a galaxy far, far away . . .

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