NeverLAN CTF 2017 - Write-ups

Monday 27 February 2017 (2017-02-27)

Saturday 14 September 2024 (2024-09-14)

🇬🇧

Information#

Version#

By	Version	Comment
noraj	1.0	Creation

CTF#

Name : NeverLAN CTF 2017
Website : neverlanctf.com
Type : Online
Format : Jeopardy
CTF Time : link

50 - Encoding Apprentice - Trivia#

What common encoding practice’s title contains the square of 8 and occasionally ends with an “=”, or “==”?

Answer: base64

50 - Shifty Ciphers… - Trivia#

What cipher is the shiftiest of them all? He even has his own salad…

Answer: caesar

50 - Know your extensions - Trivia#

Unix and Linux use this (instead of a file extension) to determine what format a file is.

Answer: magic numbers

50 - Mmmm... SSL - Trivia#

What is the standard, secure, size of an ssl certificate?

Answer: 2048

50 - Don't eat me - Trivia#

I allow HTTP to act as a stateful protocol instead of the stateless protocol it actually is. Just a small piece of data sent from a website...

Answer: cookie

50 - NeverLAN - Recon#

We've been known to leak things on twitter...

Go to NeverLanCTF twitter: https://twitter.com/NeverLanCTF

There is an interesting twitter status:

Rnfl erpba vf rnfl. synt{vas0ezngvba_vf_c0jre_xa0j_l0he_nqirefnel} #CommonCaeserCipher

I tried a rot13 and I got that:

Easy recon is easy. flag{inf0rmation_is_p0wer_kn0w_y0ur_adversary}

Flag is inf0rmation_is_p0wer_kn0w_y0ur_adversary.

100 - Purvesta - Recon#

Purvesta also really likes his twitter...

NeverLAN CTFTime page: https://ctftime.org/team/32118
purvesta CTFtime page: https://ctftime.org/user/23157

purvesta name is: Tanner Purves, his LinkedIn page is not working. So I searched for twitter Tanner Purves and found his twitter page @purvesta0704.

His twitter descripton says:

\\\BSU '20, Co-founder of the NeverLAN CTF/// {ZmxhZ3tXMHdfeTB1X0FyM19HZXR0aW5nX2cwMGRfYXRfVGhpNX0=}

It looks like a base64 string:

$ printf %s 'ZmxhZ3tXMHdfeTB1X0FyM19HZXR0aW5nX2cwMGRfYXRfVGhpNX0=' | base64 -d
flag{W0w_y0u_Ar3_Getting_g00d_at_Thi5}

50 - SoYouLikeMusic - Forensics#

SoYouLikeMusic.class

We can use strings on the java class:

$ strings SoYouLikeMusic.class
scan
Ljava/util/Scanner;
<init>
Code
LineNumberTable
main
([Ljava/lang/String;)V
decompilingTheCodeNow
qOne
StackMapTable
qTwo
qThree
playGame
SourceFile
SoYouLikeMusic.java
java/util/Scanner
OAhh welcome... so I hear you like music? What might I call you fellow listener?
java/lang/StringBuilder
Well
4, let's play a game and see how much you like music.
UWho was the special artist to dj music for our live streams before the event started?
    s7a73farm
Try Again...
@Now you are on a roll! What is zestyfe's favorite type of music?
dubstep
=Final Question! What is the name of purvesta's only rap song?
The_Gettysburg_Address_Rap
|I will ask you three questions. If you can answer them all right, then I will point you towards your precious flag you seek!
Want to play? (y/n)
;Great let's play! (ctrl-c if you really don't want to play)
Congratulations!! You did it!!
8ZmxhZ3tTdGlsbF9XYWl0aW5nX09uX3B1cnZlc3RhJ3NfTWl4dGFwZX0=
SoYouLikeMusic
java/lang/Object
java/lang/String
java/lang/System
Ljava/io/InputStream;
(Ljava/io/InputStream;)V
Ljava/io/PrintStream;
java/io/PrintStream
println
(Ljava/lang/String;)V
nextLine
()Ljava/lang/String;
trim
append
-(Ljava/lang/String;)Ljava/lang/StringBuilder;
toString
equals
(Ljava/lang/Object;)Z
equalsIgnoreCase
(Ljava/lang/String;)Z
exit
(I)V

Focus on:

Congratulations!! You did it!!
8ZmxhZ3tTdGlsbF9XYWl0aW5nX09uX3B1cnZlc3RhJ3NfTWl4dGFwZX0=

That looks like base64:

printf %s '8ZmxhZ3tTdGlsbF9XYWl0aW5nX09uX3B1cnZlc3RhJ3NfTWl4dGFwZX0=' |base64 -d
񙱅��Mѥ��}]��ѥ��}=�}���ٕ�ф��}5��х���base64: invalid input

That's wrong let's execute the java class, we know the answers:

$ java -cp . SoYouLikeMusic
Ahh welcome... so I hear you like music? What might I call you fellow listener?
alex

Well alex, let's play a game and see how much you like music.
I will ask you three questions. If you can answer them all right, then I will point you towards your precious flag you seek!
Want to play? (y/n)
y

Great let's play! (ctrl-c if you really don't want to play)

Who was the special artist to dj music for our live streams before the event started?
s7a73farm

Now you are on a roll! What is zestyfe's favorite type of music?
dubstep

Final Question! What is the name of purvesta's only rap song?
The_Gettysburg_Address_Rap

Congratulations!! You did it!!
ZmxhZ3tTdGlsbF9XYWl0aW5nX09uX3B1cnZlc3RhJ3NfTWl4dGFwZX0=

There was only a 8 before our base64 string:

$ printf %s 'ZmxhZ3tTdGlsbF9XYWl0aW5nX09uX3B1cnZlc3RhJ3NfTWl4dGFwZX0=' | base64 -di
flag{Still_Waiting_On_purvesta's_Mixtape}

Note: This is not forensics.

300 - just-a-selfie - Forensics#

You've been put in charge of a very secret project. There's talk that some of your data has leaked out. Your security analyst has flagged this email as "out of place". Has your company been breached?

Hmm.. Binwalk.

Now that's a useful tool!

$ file email.txt
email.txt: SMTP mail, ASCII text

This is a mail with a attached image.

--Apple-Mail=_9C94B8C8-A2CF-4892-8E1B-A89A4C3EAE03
Content-Transfer-Encoding: base64
Content-Disposition: inline;
    filename=selfie.jpg
Content-Type: image/jpeg;
    x-unix-mode=0644;
    name="selfie.jpg"
Content-Id: <456C033A-8B84-4975-B1DC-3E5820C8993A@death.star>

The image is base64 encoded, and split between line 92 and line 12617.

Of course, binwalk is useless here:

        0x559           HTML document header
        0xFA3           HTML document footer
        0x25D9          Unix path: /WqckbqxDJsHoQRUjuIXZONp/Kk81v7p/KjzN4BFG73qguf/0Pu9
       0x2B4D          Unix path: /4RD4Z6ZCUZZplNxIrjBy/I/QgV9N/DfxvL4aeO+t0
       0x33AD          Unix path: /ENn/Y/huxtvl8wx5Yrjljz/XFcVZQtPdqFRpH3DhFzntj8eK7L4h3
       0x33E4          Unix path: /nakVUgImCE9BjOK2f2dPAx8c/F/w/p+zfD9pW4kA4+SP5mz7dK8OeIjhsJKtN7Js/Sc0pxnmnsl
       0x38E0          Unix path: /wCEI0L/AJ8I/wDvqtxbcOoY/KTz6Uv2
       0x3BB7          Unix path: /qK6f4i/C/VfHGu/wBs+MdbXXmhwEuZIRFIUAGAQuOn1P0rxLRVlc+hdp6rRI8RvvDfhTxRpk8h
       0x58A8          Unix path: /8E/Ke8hMUKjeWAOBkde/9c/jVZIhnPfvmr2or8qZwpPJHFVQm7ngjsDWt
       0x5ACA          Unix path: /jivyX2F9h6LjJ/P/J/GvqMszD+0Kcm1ZrcqbhUh7WGielgaMcY
       0x63B7          Unix path: /VX4Z/sceA/B/hq2iksI7rUFjAedu/Gf5ivMlZaHq+1jSXNI/P8A+FHxw1DwhrDWGlBbnT3bZLay
       0x6927          Unix path: /g9Ya7q2iG9/4SKO4Xz1zss1b/AFYcehBbrXxjjLmaPufiimmec/DD4VaN4j1K8uIbWym1
       0x74EF          Unix path: /AI/pTd3IVudkZwoPsWP/AI7X2XdzLDG7M20AE5r8q/2lvHLfED4yeIL/
       0x8242          Unix path: /8d2V8h6gAHRADuC54969P/aJ8X/8ACc/H
       0x8BDA          Unix path: /KvZNS/bO8a61EBdzJLFghkZuAOR1/Ovn74k/FC58Q
       0x9040          Unix path: /klCp/1gIwfY1z2sSrIxWX5to/vYrQ4iLU/FsiXLyLB5MucoAPlj/xrKufEV1e4S4K/NyGB
       0xA780          Unix path: /a/E/hDRQwxbWk1y/PQu4Uf+i/1r4a1Ihrjysj93x07100aM
       0xA8F9          Unix path: /Z8yuKjGpSany/ebZ8P6bqWDG/2Vm/ij5H5Gsq/8K3FmC0bxzpuyD0Ki
       0xC025          Unix path: /rtr4UWLzdoB3Z/Kvfv2z/GR8UfGaewhfdaaLAtoo3Y/eHDuf1A/C
       0xC444          Unix path: /ljkcgHrV/RNXOm6pFLjMT/LKnHzr3WgpMr5AA2/xVteG5f3k0bN6HH+fwqprmnHTbwmI7rOb95B
       0xCFB8          Unix path: /8E7tBW30/xJrEsflyTMlvE5/iGSWA/Ja+HzKq6OAqS6yP0PMKqipQh9iKXzPt7Tvml5rY
       0xD6FA          Unix path: /wBivxnBfOmn6hp91bfwySPsY/UGqX/DGPxA/wCfjTP+/wAK+8fIP90n8KPI
       0xEB38          Unix path: /TRd66LiUARWaeeWI6sDhV/U/lT/F1+19qUuO
       0xFF3B          Unix path: /AMBrzL/hb3ib/oI3X5mvAdFXPSWHbSZ//9P4g8A+Ab3VNM1HxQztJpem3kFoSSMvNKrlVwOw
       0x105BD         StuffIt Deluxe Segment (data): fpW74o1EL5VrGoBI3PhRkc
[...]

So let's extract the base64 string, join it, decode it and save the ouput in a file (with a ruby script of course).

require "base64"

line_no = 1
selfie_b64 = ""

File.open("email.txt", 'r') do |file|
    file.each do |line|
        if line_no >= 92 && line_no <= 12617
            selfie_b64 += line.chomp
        end
        line_no += 1
    end
end

selfie_plain = Base64.decode64(selfie_b64)

File.open("selfie.jpg", 'w') do |file|
    file.write(selfie_plain)
end

I obtained this picture:

$ file selfie.jpg
selfie.jpg: JPEG image data, JFIF standard 1.01, aspect ratio, density 72x72, segment length 16, Exif Standard: [TIFF image data, big-endian, direntries=2, orientation=upper-left], baseline, precision 8, 820x618, frames 3

This image seems to hide something else (trailing data):

$ binwalk selfie.jpg

DECIMAL       HEXADECIMAL     DESCRIPTION
--------------------------------------------------------------------------------
0             0x0             JPEG image data, JFIF standard 1.01
30            0x1E            TIFF image data, big-endian, offset of first image directory: 8
128969        0x1F7C9         Zip archive data, at least v2.0 to extract, name: Death_Star_Owner's_Technical_Manual_blueprints.jpg
712883        0xAE0B3         Zip archive data, at least v1.0 to extract, name: __MACOSX/
712938        0xAE0EA         Zip archive data, at least v2.0 to extract, name: __MACOSX/._Death_Star_Owner's_Technical_Manual_blueprints.jpg
713908        0xAE4B4         End of Zip archive

Then I extracted it with foremost and unzip the archive:

$ unzip 00000251.zip
Archive:  00000251.zip
  inflating: Death_Star_Owner's_Technical_Manual_blueprints.jpg  
   creating: __MACOSX/
  inflating: __MACOSX/._Death_Star_Owner's_Technical_Manual_blueprints.jpg

Finally, I get this Death Star Elevation Plan:

Flag is rebellions_are_built_on_hope.

Note: This is steganography, not forensics.

100 - TheHistoryOfCryptography - Cryptography#

The_History_of_Cryptography.zip contains two files: 0.txt and 1.zip :

$ cat 0.txt
This Shifty Cipher is one of the simplest, and most well know ciphers.

Answer: caesar

The zip is password protected and the password is the answer of 0.txt.

1.zip contains 2 files: 1.txt and 2.zip, and so on.

$ cat 1.txt
This Cipher is is named after the person who made it famous, not but the man who first created it.

Password:"The name of cipher in the riddle" with out the quotes.

Answer: vigenere

$ cat 2.txt
This transposition cipher was used by the warriors in the famous movie "the 300"

PassWord:"The name of cipher in the riddle" with out the quotes.

Answer: scytale

$ cat 3.txt
The first recorded use of this cipher was used to hide a book of magic.

Password:"The name of cipher in the riddle" with out the quotes.

Answer: steganography (details)

$ cat 4.txt
This world famous cipher was invented by Arthur Scherbius

Password:"The name of cipher in the riddle" with out the quotes.

Answer: enigma machine (details)

$ cat 5.txt
Which one is you're favorite? I love them all because...
flag{THEHISTORYOFCRYPTOGRAPHYISAW3S0M3}

Flag is THEHISTORYOFCRYPTOGRAPHYISAW3S0M3.

Note: this challenge was a quizz, not a cryptography challenge. It should have been in Trivia, Misc, Quizz or Other.

100 - A Slight Cut - Web#

http://neverlanctf-challenges-elb-248020705.us-west-2.elb.amazonaws.com:9123/

Source:

<!DOCTYPE html>
<html>
    <head>
        <title>A slight cut</title>
        <script src="js/jquery.js"></script>
        <script>
[...]
        </script>
    </head>
    <body>
        <div>
            <h1>type in some text to have the server repeat it back</h1>
            <form onsubmit="getEcho(); return false;">
                <input id="text" name="text" type="text" placeholder="type some text here"/>
                <input id="length" type="hidden" name="length" value="0"/>
                <input type="submit"/>
            </form>
            <p id="echo">output will appear here</p>
        </div>
    </body>
</html>

There is two parameters in te request url: length and text. text comes from the input field, and length is calculated with javascript.

function getEcho(){
    var text = $('#text').val();
    var length = $('#length').val();
    $.ajax('echo.php?length='+length+'&text='+text).done(function(echoed){
        $('#echo').text(echoed);
    });
}
$(document).ready(function(){
    $('#text').on('input', function(){
        $('#length').val($('#text').val().length);
    });
});

If I submit A, the calculated length is 1.

GET /echo.php?length=1&text=A HTTP/1.1
Host: neverlanctf-challenges-elb-248020705.us-west-2.elb.amazonaws.com:9123
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:51.0) Gecko/20100101 Firefox/51.0
Accept: */*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://neverlanctf-challenges-elb-248020705.us-west-2.elb.amazonaws.com:9123/
X-Requested-With: XMLHttpRequest
Connection: close

But what will happen if I change the value from 1 to 1000 with Burp:

GET /echo.php?length=1000&text=A HTTP/1.1

The server displays more than intended:

Auo$@uyc kds2^4a ady 5 tyusft tuyuy_#65afajty ajb tjuflt ty%&(juuyttyjtji KEY: flag{bleeding_in_javascript} SDF4 asd6f ayj1dsgff@ af ttmtum56tu$%ga wrg3@#%aa9-mtyumty dfgsaumg68g$%ershe as 9tuyt t9uty38dsdfg-5f htyd45s#$

Flag is: bleeding_in_javascript.

300 - WebCipher - Web#

#anti-human

http://neverlanctf-challenges-elb-248020705.us-west-2.elb.amazonaws.com:7129/

word list:

https://s3-us-west-2.amazonaws.com/neverlanctf/files/words.txt

Source:

<!DOCTYPE html>
<html>
    <head>
        <title>anti-human cipher</title>
    </head>
    <body>
                <div id="cipher_box">
            <h1 id="cipher">shhsjwfl</h1>
        </div>
        <div id="form_box">
            <form id="form" method="GET" action="?">
                <input type="text" name="deciphered" id="deciphered"/>
                <input type="submit"/>
            </form>
        </div>
    </body>
</html>

First thing is to understand what to do. Here is what the server do:

A word is picked up randomly from words.txt
This word is randomly rotated (Caesar cipher with a shift between 1 and 25)
Then the shifted word is displayed for a few seconds
A new word is picked up and so on...

So we need a script that:

Get the shifted word
Cross the dictionary and test words one by one (only same length as the shifted word)
For each tested word try all possible shifting
Break when that match
Send the answer (decipered/unshifted word)
Get the flag

So that's what I did with a ruby script and curb:

$ ruby webcipher.rb
• Connexion works
• Cracking ciphered word
• Deciphered: cassidony
• Sending answer
• Flag: c34s3r_c1ph3r_70_7h3_m4x

My ruby script:

#!/usr/bin/env ruby

require 'curb' # for get/post requests

# from https://gist.github.com/matugm/db363c7131e6af27716c
def caesar_cipher(string, shift = 1)
    alphabet   = Array('a'..'z')
    encrypter  = Hash[alphabet.zip(alphabet.rotate(shift))]
    string.chars.map { |c| encrypter.fetch(c, " ") }
end

hostname = 'http://neverlanctf-challenges-elb-248020705.us-west-2.elb.amazonaws.com:7129/index.php'

c = Curl::Easy.new(hostname) do |curl|
  curl.headers['Cookie'] = 'PHPSESSID=30ff4361f8af2985595bff7c9614b1f1'
  curl.headers['Referer'] = hostname
  curl.headers['Upgrade-Insecure-Requests'] = '1'
  #curl.verbose = true
end # Curl

c.perform # send the request
if c.body_str.match(/anti\-human cipher/)
  puts '• Connexion works'
end

# get the cipher word
ciphered_word = c.body_str.match(/<h1 id="cipher">([a-zA-Z]*)<\/h1>/).captures[0]
ciphered_word.downcase! # put lowercase
ciphered_word_length = ciphered_word.length

puts '• Cracking ciphered word'
do_break = false
answer = ""
File.open("words.txt", 'r') do |file|
    file.each do |word|
        word.chomp! # remove spaces
        if word.length.eql?(ciphered_word_length) # only try word with same length
            answer = word # save the word because it can be mixed case
            word.downcase! # put lowercase
            # puts "word: #{word}"
            (1..25).each do |i|
                # puts caesar_cipher(word, i).join
                if caesar_cipher(word, i).join == ciphered_word
                    puts "• Deciphered: #{word}"
                    do_break = true
                    break
                end
            end
        end
        break if do_break
    end
end

puts "• Sending answer"
c.url = hostname.concat("?deciphered=#{answer}")
c.perform

puts "• Flag: ".concat(c.body_str.match(/<p>flag{(.*)}<\/p>/).captures[0])

Note: This is not web, this is scripting.

50 - Master Mind 1 - Other#

Can you break my three digit lock?

MasterMind1.txt

Source:

+-----------------------+
|       |       |       |
|   7   |   3   |   6   | One number is correct but wrongly placed
|       |       |       |
|_______|_______|_______|
|       |       |       |
|   0   |   6   |   5   | One number is correct and correctly placed
|       |       |       |
|_______|_______|_______|
|       |       |       |
|   3   |   7   |   2   | Two numbers are correct but wrongly placed
|       |       |       |
|_______|_______|_______|
|       |       |       |
|   6   |   4   |   7   | No numbers are correct
|       |       |       |
|_______|_______|_______|
|       |       |       |
|   5   |   2   |   4   | One number is correct and correctly placed
|       |       |       |
|       |       |       |
+-----------------------+

Rules: Mastermind

Code-breaking:

Line 4: 647, No numbers are correct => [0,1,2,3,5,8,9] are possible
Line 1: 736, One number is correct but wrongly placed => 7 and 6 are wrong, so 3 is in the code and is right or left
Line 2: 065, One number is correct and correctly placed => 6 is wrong, so 0 or 5 is in the code and corrctly placed
Line 3: 372, Two numbers are correct but wrongly placed => 7 is wrong, 3 and 2 are good so [3,2,[0|5]] are possible
Line 5: 524, One number is correct and correctly placed => Only one number is correct, 2 is good so 5 is wrong and [3,2,0] are possible
(We have the three numbers so now let's order them)
Line 5: 524, One number is correct and correctly placed => 2 is middle
Line 2: 065, One number is correct and correctly placed => 0 is left
So 3 is right

Flag is 023.

100 - Master Mind 2 - Other#

I've upgraded my lock! Can you solve it?

MasterMind2.txt

Source:

+-------------------------------+
|       |       |       |       |
|   9   |   5   |   3   |   2   | One number is correct but wrongly placed
|       |       |       |       |
|_______|_______|_______|_______|
|       |       |       |       |
|   1   |   6   |   7   |   3   | Two numbers are correct and correctly placed
|       |       |       |       |
|_______|_______|_______|_______|
|       |       |       |       |
|   0   |   6   |   5   |   9   | Two numbers are correct but wrongly placed
|       |       |       |       |
|_______|_______|_______|_______|
|       |       |       |       |
|   2   |   4   |   3   |   8   | No numbers are correct
|       |       |       |       |
|_______|_______|_______|_______|
|       |       |       |       |
|   5   |   2   |   4   |   0   | One number is correct and correctly placed
|       |       |       |       |
|       |       |       |       |
+-------------------------------+

Rules: Mastermind

Code-breaking:

Line 4: 2438, No numbers are correct => Only [0,1,5,6,7,9] are possible
Line 5: 5240, One number is correct and correctly placed => 2 and 4 are wrong, so 0 or 5 is in the code, [[0|5],1,6,7,9]
Line 1: 9532, One number is correct but wrongly placed => 2 and 3 are wrong, so 9 or 5 is good, [0|5] & [5|9] = 5 so [1,5,6,7] OR [0|5] & [5|9] = [0,9] so so [0,1,6,7,9]
Line 2: 1673, Two numbers are correct and correctly placed => Only two number are good so [1,5,6,7] impossible so [0,1,6,7,9] is only possible
(Now we need to filter the 5 numbers to keep only 4)
Line 1: Confirmed [9], Possible [0,1,6,7]
Line 3: Confirmed [9,[0|6]], Possible [1,7]
Line 5: Confirmed [9,0], Possible [1,7] so [0,1,7,9] are the four numbers
(We have the four numbers so now let's order them)
Line 2: Place [1,x,7,x]
Line 5: Place [1,x,7,0] so [1,9,7,0]

Flag is 1970.

writeups

Information#

Version#

CTF#

50 - Encoding Apprentice - Trivia#

50 - Shifty Ciphers… - Trivia#

50 - Know your extensions - Trivia#

50 - Mmmm... SSL - Trivia#

50 - Don't eat me - Trivia#

50 - NeverLAN - Recon#

100 - Purvesta - Recon#

50 - SoYouLikeMusic - Forensics#

300 - just-a-selfie - Forensics#

100 - TheHistoryOfCryptography - Cryptography#

100 - A Slight Cut - Web#

300 - WebCipher - Web#

50 - Master Mind 1 - Other#

100 - Master Mind 2 - Other#