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+---- Thread: [Vibe] Community CTF #03 - Find the Flag (/showthread.php?tid=6321750)
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Community CTF #03 - Find the Flag - Vinavil - Mar 12, 2026
![[Image: Vibe-Header.gif]](https://i.ibb.co/4RGC0JNd/Vibe-Header.gif)
— Community CTF #03 —
Find the Flag
Find the Flag
FIRST 3 WINNERS WILL BE ANNOUNCED IN THIS THREAD
🏆 HerrWinston @loadman@
Only 2 winners for this challenge.
This is a reverse engineering challenge created and managed by @Vinavil@. Download the binary below and find the hidden flag.
Flag format: vibe{...}
Difficulty: Medium
Official Hint: The key isn't what it seems. Look closer.
Rules: Do NOT share hints, clues, or the answer in this thread. PM Vinavil directly with the correct flag. First 3 correct submissions win.
Download: crackme_03
Official Walkthrough
1. Open Ghidra, create a new project and import the binary. Let auto-analysis run with default settings. Since the binary is stripped, navigate manually through Functions in the Symbol Tree and find the one calling printf and fgets.
2. In the decompiler you will find a validation loop. The input bytes are being XOR'd against a value before being compared to an encoded array stored in the binary. Your first instinct will be to grab that value and use it as the key that is the wrong move.
3. Look closer. The XOR value is not a constant. It comes from a separate function that gets called on every iteration with the current index as argument. Click into that function and read it carefully. It performs a small arithmetic operation using three values combined together, one of which changes based on the index. This means every byte of the flag is encrypted with a different key.
4. Once you fully understand the key derivation logic, locate the encoded byte array in the Listing view. It is 30 bytes long.
5. Replicate the key derivation logic yourself in Python, CyberChef, or even by hand. Apply it to each byte of the encoded array. The output is the flag.
6. Submit to Vinavil via PM.
This is a step up from CTF #02. More challenges are coming. Good luck.
Also a special thanks to 7 for making this possible!
Also a special thanks to 7 for making this possible!
![[Image: vibesignature.gif]](https://i.ibb.co/8LvxwtYQ/vibesignature.gif)
RE: Community CTF #03 - Find the Flag - Hackers - Mar 12, 2026
Get the submissions in, you don't want to be #4+ !
RE: Community CTF #03 - Find the Flag - InspectorGadget - Mar 12, 2026
Sadly I'm at work for another 3 hours so people are probably going to beat me :(
To accommodate timezones, perhaps instead of 3 'fastest first ' winners, you could allow all winners within 24 hours and rank them in order of flag submission.
Should provide an incentive for people who can't check for the thread at the same time on most days. ❤️
RE: Community CTF #03 - Find the Flag - Money- - Mar 12, 2026
I want more web challenges!
RE: Community CTF #03 - Find the Flag - 7 - Mar 12, 2026
(Mar 12, 2026 07:05 AM)Money- Wrote: I want more web challenges!
Your wish is Vibe's command!
More web challenges Vibe!
RE: Community CTF #03 - Find the Flag - Vinavil - Mar 12, 2026
(Mar 12, 2026 07:06 AM)7 Wrote: Your wish is Vibe's command!
More web challenges Vibe!
On the way!
(Mar 12, 2026 06:57 AM)InspectorGadget Wrote: Sadly I'm at work for another 3 hours so people are probably going to beat me :(
To accommodate timezones, perhaps instead of 3 'fastest first ' winners, you could allow all winners within 24 hours and rank them in order of flag submission.
Should provide an incentive for people who can't check for the thread at the same time on most days. ❤️
I'll work on a public sharable dashboard, that sound cool right? LOL
RE: Community CTF #03 - Find the Flag - Au Jus Demon - Mar 12, 2026
(Mar 12, 2026 07:19 AM)Vinavil Wrote: On the way!
I'll work on a public sharable dashboard, that sound cool right? LOL
Could end up making something like the H4CK3R$ have with their missions.
RE: Community CTF #03 - Find the Flag - HerrWinston - Mar 12, 2026
I have sent you the full explanation and final answer, hopefully everything is right and understandable, great night and awesome CTF !!
RE: Community CTF #03 - Find the Flag - Pοιsonlεaf - Mar 12, 2026
I like these but as I told Hackers yesterday, I doubt I'm doing these as intended xD
idk I'm more about doing it reverse engi on the source code with python.
RE: Community CTF #03 - Find the Flag - InspectorGadget - Mar 12, 2026
(Mar 12, 2026 12:39 PM)Pοιsonlεaf Wrote: I like these but as I told Hackers yesterday, I doubt I'm doing these as intended xD
idk I'm more about doing it reverse engi on the source code with python.
The way I see it, if you get the flag, then it doesn't matter if it's as intended.
RE: Community CTF #03 - Find the Flag - Vinavil - Mar 12, 2026
Still haven't got 3 answers keep trying guys
In 24 Hours i will be posting the only winner of this Challenge!
RE: Community CTF #03 - Find the Flag - loadman - Mar 14, 2026
link is dead ?
RE: Community CTF #03 - Find the Flag - Biggy_Asian - Mar 14, 2026
This content is no longer available.
RE: Community CTF #03 - Find the Flag - Hackers - Mar 14, 2026
(Mar 14, 2026 05:12 AM)loadman Wrote: link is dead ?
(Mar 14, 2026 05:12 AM)Biggy_Asian Wrote: This content is no longer available.
You can DL challenge 3 here:
https://mega.nz/file/pillBJqA#C6shF2xmdLn73nC4_ONphlDmOISuT9pXvs8cqy9N1Nc
RE: Community CTF #03 - Find the Flag - Vinavil - Mar 14, 2026
Link expired due to challenge closing. In the next hour ill be announcing the winners.