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L3akCTF 2025 Write-up

Write-up for L3akCTF 2025 by AppleTree, part of team APISec Avengers. Focused heavily on OSINT challenges with GeoGuessr-style tasks.

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L3akCTF 2025 Write-up

L3akCTF 2025 Write-up

Author: AppleTree
Team: APISec Avengers
Event Dates: July 11–13, 2025
Platform: ctf.l3ak.team
Duration: 48 Hours
Total Challenges: 64
Categories: Crypto, Pwn, Rev, Web, Misc, Mobile, Forensics, Hardware/RF, OSINT, Hash Cracking
Flag Format: L3AK{[ -~]+}

TL;DR

I focused primarily on the OSINT challenges, which followed a GeoGuessr-style format requiring geographic deduction from images. Due to time constraints, I only contributed a couple hours on July 12 and about 30 minutes on July 13. I completed 6 challenges (5 OSINT, 1 Misc) worth 300 total points.

My teammate Jesse Freeman handled two Web challenges for another 291 points, bringing our team total to 591 points and a final ranking of 391st place.

Sanity Check (Misc, 50 points)

Challenge Description:

Welcome To L3akCTF 2025!! Make sure to join our Discord and read the #rules!

Steps Taken:

  1. Joined the Discord server.
  2. Opened the #rules channel.
  3. Found the flag hidden in the About section.

Flag: L3AK{W3Lc0mE_t0_L3aKCTF_2025!}
Points: 50

Sunny Day (OSINT, 50 points)

Steps Taken:

  1. Identified mountainous European terrain and classic architecture.
  2. Used church and tower as landmarks.
  3. Matched features to Triesenberg, Liechtenstein.
  4. Confirmed with satellite and street view: 47.117462, 9.545970

Flag: L3AK{sUn5H1Ne_iN_L1ecHt3nSTe1n}
Points: 50

Screenshots:
Church top Tower landmark

Mountain View (OSINT, 50 points)

Steps Taken:

  1. Found signage written in Japanese.
  2. Used Picarta.ai to confirm Japan.
  3. Blossoms and path signage suggested Yoshino.
  4. Coordinates submitted: 34.356146, 135.872289

Flag: L3AK{y0sh1n0_HAs_gR3At_54KuRA_Bl0s5omS}
Points: 50

Screenshots:
Sign 1 Sign 2 Sign 3

Lost Locomotives (OSINT, 50 points)

Steps Taken:

  1. Noticed a labeled train (500).
  2. Researched and confirmed this as the Hiram Bingham Train.
  3. Narrowed location to Ollantaytambo, Peru via blog.
  4. Verified terrain and identifiers.
  5. Final coordinates: -13.263979, -72.268991

Flag: L3AK{cH00_Ch0o_1n_P3Ru}
Points: 50

Screenshots:
Train plate River + mountains Train identifier

Grain of Truth (OSINT, 50 points)

Steps Taken:

  1. Focused on an electrical pole sign.
  2. Used Picarta.ai to get Taiwan, Vietnam, China candidates.
  3. Narrowed to Taiwan using font/style and terrain.
  4. Used compass-aligned views for triangulation.
  5. Final coordinates: 23.5558605, 120.4464335

Flag: L3AK{Wh0_Kn3W_El3ctr1C_p0L3S_W3R3_so_Us3FuL!}
Points: 50

Screenshots:
Pole sign Wide view North East South West

Elephant Enclosure (OSINT, 50 points)

Steps Taken:

  1. Saw a zoo-like enclosure with natural stone and foliage.
  2. Suspected Singapore Zoo.
  3. Validated the location via image match and Street View.
  4. Coordinates: 1.405245, 103.795882

Flag: L3AK{E13ph4nTs_4R3_F4sT_AF_https://youtu.be/ccxNteEogrg}
Points: 50

Screenshots:
North East

Teammate Contributions

Certay (Web, 241 points) – Jesse Freeman

Challenge Description:

Probably you need to understand our language to get some of the super powers?

Jesse’s writeup.

Flag L3ak (Web, 50 points) – Jesse Freeman

Challenge Description:

What’s the name of this CTF? Yk what to do 😉

Tools & Techniques Used

  • Google Maps & Street View
  • Picarta.ai (AI-based geolocation)
  • Reverse image search (Google & Bing)
  • Blog/forum references for identifying rare landmarks
  • Cardinal direction screenshots for triangulation

Lessons Learned

  • Picarta is extremely effective for narrowing country-level guesses
  • Mapping out all four cardinal views speeds up alignment and confirmation
  • Geoguessr-style CTFs are limited by lack of Street View in many regions
  • AI + traditional OSINT creates a strong combination for visual recon

Final Scoreboard Stats

  • ✅ 6 Challenges Solved by AppleTree
  • ✅ 2 Challenges Solved by Jesse Freeman
  • 🧠 Primary Focus: OSINT
  • 🏆 Total Points: 591
  • 📈 Final Ranking: 391st out of 2240 teams
  • 🧩 Total Challenges Available: 64
    • 5 Misc (plus 1 Feedback)
    • 8 OSINT
    • 5 Hash Cracking
    • 10 Reverse Engineering
    • 4 Mobile
    • 9 Crypto
    • 6 Forensics
    • 7 Pwn
    • 8 Web
    • 2 Hardware/RF

Note: AI-assisted editing was only used to format into markdown headings and frontmatter. All technical content and steps remain original.

CTF Writeups
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