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JU Bootcamp CTF — Writeup

A7reus // // 10 min read
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My solutions to the problems on JU Bootcamp CTF hosted by Cyber Bangla.

CTF Poster

Section 1: Basics

Problem 1: Digital Image Metadata Analysis

While investigating digital evidence, you come across a series of JPEG image files. Although they appear ordinary at first glance, you suspect they may contain embedded metadata - such as timestamps, geolocation data, or camera details - that could link them to key events or locations.

Question:
Which tool is best suited for extracting metadata from image files?

Options:
A. ExifTool
B. Wireshark
C. Volatility
D. FTK Imager

Flag Format: CBCTF{C}

ExifTool is the correct answer.

Problem 2: Email Header Analysis

You receive a suspicious phishing email. To trace its origin, you want to analyze the "Received" headers and IP information.

Question:
Which tool is best suited for analyzing and visualizing email headers?

Options:
A. Autopsy
B. MXToolbox
C. Nmap
D. Hashcat

Flag Example: CBCTF{B}

MXToolbox is the correct answer.

Problem 3: Remove

I need to remove a file called secret in my home directory. Which command should i use?

Flag Format: CBCTF{command}

rm $HOME/secret

Problem 4: Website Footprinting

During reconnaissance, you want to gather subdomains of a target website to identify potential attack surfaces.

Question:
Which tool is specifically designed for subdomain enumeration?

Options:
A. DirBuster
B. Sublist3r
C. Burp Suite
D. Wireshark

Flag Example: CBCTF{C}

Sublist3r is the correct answer.

Problem 5: Satellite Spy

Which free service provides satellite images useful for OSINT?

Flag Format: CBCTF{FlagFlag}

There can be more than one answer to this one, but Google Eath is the most well-known choice.

Problem 6: Scout

Which search engine is designed to find Internet-connected devices?

Flag Format: CBCTF{flag}

Shodan is the answer.

Problem 7: Secrets

Developers often leak sensitive information accidentally. Which platform is often searched?

Flag Format: CBCTF{******}

Github is the most logical answer to this one.

Problem 8: Image

What technique helps identify the source of an image by searching visually similar ones?

Flag Format: CBCTF{FlagFlagFlag}

The technique is called reverse image search.

Section 2: Cryptography

Problem 1: Welcome

Welcome

Q0JDVEZ7d2VsY29tZV90b19jYmN0Zn0=

Clearly, we're given a cipher text. I used dcode.fr as a tool for both cipher identification and decoding.

decode.fr identifies the given text as a Base64 cipher. Decoding it yields:

CBCTF{welcome_to_cbctf}

Which is the target flag.

Problem 2: BASE

Can you decode the hidden message ?

VTJ4V1JGWkZXamROVmpselRVaFplbGd5U1RCT1ZFNW1UbXBTT1E9PQ==

This one is also a Base64 cipher. Decoding it yields another Base64, and decoding which yields yet another Base64 cipher. After 3 steps of decoding using the same Base64 coding, we get:

JUCTF{1_l0v3_b453_64}

Which is the flag.

Problem 3: আহারে…………………… 🥲🥲🥲

আমার এই দুই যুগ, অর্থাৎ ২৪ বছর বয়সে, বহুবার ট্রেনে ওঠা হয়েছে এবং বিভিন্ন জায়গায় বেড়ানো হয়েছে। তবে এক দেশ থেকে অন্য দেশে ট্রেনে করে কখনো যাওয়া হয়নি।

CCFbaoyugti}BT{rv_o_o_t

Haven't yet solved.

Problem 4: relax

Decode this
zna_vf_cbjreshy

Flag Format: CBCTF{flag}

After trying a couple of encodin methods detected by decode.fr, we get the following from ROT-13 decoder.

man_is_powerful

Which is the flag, provided that the answer format is maintained.

Problem 5: Meaty Signals

We found a strange message written using symbols like '@' and '^'.\

At first glance, it looks meaningless - but something tells us there's a pattern. We heard the sender is a fan of classic ciphers and hides messages using only two symbols. They claim the message contains a hidden flag. Can you figure out the method and decode the original message?

@@@^@ @@@@^ @@@^@ ^@@^@ @@^@^ @@^^^ @^@@@ @@@^^ @@@^^ @@^@@ @^^@@ @^@@@ ^@@@^ ^@@^@ @@@@@ ^@@@^ ^@@^@ ^@^^@

This s a Bacon cipher. Upon decoding, one of the following should be the answer format.

CBCTFHIDDENISTASTY
CBCTF{HIDDENISTASTY}
CBCTF{HIDDEN_IS_TASTY}

None of them were accepted, quetion might be rigged.

Problem 6: BrainF**k

This cryptic text doesn't follow the rules of traditional ciphers,it feels more like a language crafted by programmers. Unusual? Definitely. Secure? Perhaps. Your task: decode the madness, break through the abstraction, and uncover the hidden flag. Can you crack the code before it cracks your mind?

++++++++++[>+>+++>+++++++>++++++++++<<<<-]>>> - -.-.+.> - - - - - - - - .<+++.>+++++++++++++++++++++++++++++++++++++++. - - - - - - - - - - - - -.++++++++++++++++.← - - - - - - - - . - -.> - - .<+++++++++++++++++++++.> - - - - - - - -.++++.++++++++. - - - - - - .<<+++++++++++++++++++.>>++++++++++++++++++++. - - - - - - - - - - .++++++++++++++++++++++++.<<++. - .>> - - -. - - - - - - - . - - -.+++++++++++++++++.<<-.>>+++++++.<<+++.>> - - -. - - - - - - .+++++++++++++++.<←.>>++++++++.

This one is one of the easiest problems, since the answer is in the question itself. The text is acually code written in the programming language Brainfuck, and executing it through an online compiler yields the flag:

CBCTF{br41nF_ck_1s_w31rd_p0w3rfu1}

Problem 7: Keyboard Ninja

The message below has been encoded by shifting each character to another key on the keyboard. VNVYG}l4un-stf+v2[j4t+2d+gim|

Flag Format: CBCTF{********}

Shift each character by a key to the left (according to keyboard layout), and the flag is decoded.

CBCTF{k3yb0ard_c1ph3r_1s_fun}

Problem 8: Librarian's Secret

Long ago, in a forgotten archive of Cyber Bangla's old server,a message was left behind, encrypted by someone known only as Emran. He wasn't just a librarian; he was the guardian of secrets, a master of codes. Before he disappeared, he left a final message, and like always, he used his favorite cipher, and signed it in his own way.

GNTTS{lmtk_jsdcd_gspry_lsg_nia}

Flag Format: CBCTF{flag}

This one's encoded using Vigenere cipher, and the key used is EMRAN, which is the given name of the lirbarian. Decoding using the key, we get:

CBCTF{hack_world_today_you_win}

Problem 9: Dots & Dashes

A secret message is hidden using just dots and dashes. Can you decode this classic communication method and find the flag?

 - .. - - - . ..-. … - .. - .- … - .- . - . - - - - .- . - - .- - .. - .- . - - ..-. .. - .- - - - -. - - .- .. - .- - - …. - . .. - .- - - - - -. - - .-

Haven't yet solved.

Section 3: Web

Problem 1: Get The Flag

Just get the flag.

Flag Format: CBCTF{flag_here}

Upon visiting the given site URL, we're presented with the following text:

You might not GET it. So what would you do?

This line hints that the problem has something to do with HTTP request methods. Since a GET reqeust doesn't give us the answer, let's try to send a POST request next.

curl -X POST <URL>

And the flag can be found within the HTML returned by the server.

<div class="flag">
  Congratulations! Here's your flag:
  <b>CBCTF{YeAh_Y0u_P0St_iT}</b>
</div>

Problem 2: Secret Note

Notes are private and meant to stay hidden. Read someone else’s secret.

Flag Format: CBCTF{flag}

Upon visiting the given site, two things are clear:

  • There is no authentication going on.
  • Server depends on the query parameter id to retrieve information, which can be altered by the client.

Upon setting id=2 on the query parameter, we get the desired flag.

Username admin
Role admin
Email admin@admin.com
Note Restricted profile. You should not be able to view this directly.
Flag CBCTF{4ccess_The_@dmin_!nfo}

Problem 3: Get The Flag 2

Get the flag again but this time you might need to request the flag.

Flag Format: CBCTF{flag}

At first glance at the given site:

You might not GET it. So what would you do? It's not the same. Try requesting the flag.

The first thing that comes to mind is sending a request body with the POST request. After trying some combinations, this request worked:

curl -s -X POST 103.40.156.214:8050 -d "flag=true"

And is flag is in the response HTML:

<div class="flag">
  Congratulations! Here's your flag: CBCTF{Y3AH_Y0U_P0SteD_iT_WiTh_Fl4G}
</div>

Problem 4: Sneaky Search

The search box shows what you type. Make it do a trick when the results appear.

Flag Format: CBCTF{flag}

This one has an XSS vulnerability. All we have to do for the flag is input flag and submit.

🎉 You got the flag: CBCTF{C00k!e_Hij@cked_vi@_X$$}

Section 4: OSINT

Problem 1: Where Hackers Meet

I’m a legendary cybersecurity conference held every August in Las Vegas. Hackers from all over the world gather under one roof — but don’t bother bringing your credit card, I only deal in cash. Who am I?

DEF CON.

Problem 2: Elephant

Abdullah Al Naowal Dhrubo recently posted an image of an elephant he drew himself. At first glance, it looks like a simple art post — but the caption seems unusual. It contains a strange string of random letters and symbols.

JUCTF{flag}

Navigating to the said person's facebook account, we do see a post with a drawing of an elephant, along with a caption that looks like a Base64 ciphertext.

Upon decoding, we get:

Hint: It's good to make changes in life every now and then.

Which is clearly not the flag. Upon further inspection, it seems that the post has been edited. The edit history helps us find the original version of the post, which contains the ciphertext that actually contains our flag. Decoding it yields:

JUCTF{yeaaa_you_the_flag_base64}

Problem 3: Domain Digger

One of my friends performed terribly in a recent CTF event, let’s call it examplectf.com.

Frustrated by the loss, he came to me and said: "I want revenge! Find out who runs this CTF. Get me the registration info, anything you can dig up."

Can you help him?

Flag Format: CBCTF{Registry Domain ID}

This one tool some trial and error, but running the following command managed to spot the flag.

# CBCTF{2592662472_DOMAIN_COM-VRSN}
whois examplectf.com | grep "Registry Domain ID"

Problem 4: Do you know Mrrexnomi?

Need to search the user and find the hidden message.

Obvious course of action: google Mrrexnomi. After digging the guy's social media accounts a bit, we find the following in the About section of his linkedin:

Recently, my team visited CTF Finance Centre area and dropped a message. Please find out this "https%3A%2F%2Ftextbin.net%2F4ehjkdza4a"

It's a textbin link, and the id is pretty predictable from looking at the text. We can format the link as https://textbin.net/4ehjkdza4a. Visiting the site gives us the flag:

JUCTF{Cyb3r_Bang1a_Teams}

Problem 5: Exif Escape

An image was anonymously uploaded to a public forum, claiming it was taken "somewhere in South Asia".But OSINT never lies and metadata tells a different story. We extracted this file before it was deleted. Can you investigate and find the real location?

Flag Format: CBCTF{Place Name_City_Country}

hq720.jpg

Haven't yet solved.