SWIMMER OSINT CTF 2026: Writeup
TL;DR
- Participated in SWIMMER OSINT CTF 2026 (hosted by DIVER OSINT CTF)
- Team: 0$1N7_K1dd13$
- Final rank: 200 / 688 teams
- Solved: 23 / 29 challenges
- Personally solved: 8 challenges
- Focus areas: aviation OSINT, geo-location, archival research, Japanese media OSINT
- Core tools: Google, Google Lens, OpenStreetMap, YouTube, UN Digital Library, Wikipedia
Plus Ultra.
Event Info
Swimmer OSINT CTF 2026 is a 12-hour CTF with all challenges being OSINT. Max team size is 6 and the event is held online.
- CTFtime: https://ctftime.org/event/2986
- Platform: https://swimmer.diverctf.org/
I played with teammates from $cr1pt_K1dd13$. Due to the 6-member limit, we split into two teams. I competed in 0$1N7_K1dd13$ with GregorSec, th3mujd11, Scorpius, and Codru.
- Rank: 200 / 688
- Solved: 23 / 29
- Personally solved: 8 challenges
Challenge Index
| Category | Challenge | Core Technique | Tools Used |
|---|---|---|---|
| research_2025 | cx | Aviation OSINT | Google, News Articles |
| research_2025 | pilot | Video Analysis | YouTube, LinkedIn |
| research_2025 | flag_on_the_don | Event OSINT + Geo | Google, Gemini, OpenStreetMap |
| research_2025 | obsolete | Archival Research | UN Digital Library, Google |
| research_2025 | truck | Geo + Video OSINT | Google Maps, 11foot8.com |
| research_2025 | debris | Geo-location | YouTube, Google Maps |
| tgt_rain | rain_04_source2 | Reverse Image Search | Google Lens, Wikipedia |
| tgt_rain | rain_05_date | Event Correlation | LinkedIn, Image Analysis |
research_2025
cx
Tools: Google, News Articles
Description In Spring 2025, a special flight commemorated the 100th anniversary of an airport that once existed in Hong Kong. Find the flight number.
Flag: SWIMMER{CX8100}
Write-up
I searched for combinations of:
“special flight Hong Kong 100th anniversary 2025”
This led me to the following article: https://campaignbriefasia.com/2025/04/11/flight-cx8100-takes-off-cathay-soars-once-more-over-kai-tak-in-tribute-to-legendary-flight-path/
The article clearly states that Cathay Pacific operated flight CX8100 to commemorate the Kai Tak Airport flight path anniversary.
pilot
Tools: YouTube, LinkedIn
Description Identify the person sitting in the indicated seat on flight CX8100.
Flag: SWIMMER{Adrian Scott}
Write-up
I reviewed related articles and videos about flight CX8100:
The crew consisted of: Geoffrey Lui, Adrian Scott, Boris Wong, Darren Palmer.
The YouTube footage clearly shows Adrian Scott seated on the right-hand side, matching the seat diagram in the challenge image.
flag_on_the_don
Tools: Google, Gemini, OpenStreetMap
Description On August 28th 2025, an event using Taiko no Tatsujin was held in Gunma Prefecture. Find the OpenStreetMap way ID of the venue.
Flag: SWIMMER{628293186}
Write-up
I found a Japanese PDF listing city events: https://www.city.shibukawa.lg.jp/manage/contents/upload/68870b94eeb0d.pdf
I used Gemini to extract event details, confirming:
- Event date: 28 August 2025
- Venue: Shibukawa Civic Hall, Gunma
I located the venue in OpenStreetMap, enabled Map Data, clicked the building outline, and obtained the way ID: 628293186.
obsolete
Tools: Google, UN Digital Library
Description Find which countries abstained in UNGA Resolution 50/52 (1995).
Flag: SWIMMER{CUBA_DEMOCRATIC PEOPLE'S REPUBLIC OF KOREA_LIBYAN ARAB JAMAHIRIYA}
Write-up
I located UNGA Resolution 50/52 in the UN Digital Library: https://digitallibrary.un.org/record/284118?ln=en
Countries without Y/N markers were abstentions:
- CUBA
- DEMOCRATIC PEOPLE’S REPUBLIC OF KOREA
- LIBYAN ARAB JAMAHIRIYA
truck
Tools: Google Maps, 11foot8.com
Description Identify the FQDN on a truck at a given Plus Code.
Flag: SWIMMER{www.MiracleMoversUSA.com}
Write-up
The Plus Code resolved to The Can Opener Bridge, Durham.
Searching:
“The Can Opener Bridge June 21 2025”
led to: https://11foot8.com/moving-truck-runs-red-light-and-scrapes-the-11foot88-bridge/
The video clearly shows the truck branding: www.MiracleMoversUSA.com
debris
Tools: YouTube, Google Maps
Description Find where a ton bag was initially dropped.
Flag: 35.7131787, 139.7296142
Write-up
I found footage from Mezamashi Media: https://mezamashi.media/articles/-/232641 https://www.youtube.com/watch?v=xo_2KZ3n668
The controller dialogue references: Gokokuji Road, Otowa.
Using road curvature and nearby buildings visible in the footage, I matched the location in Google Maps and extracted the coordinates.
tgt_rain
rain_04_source2
Tools: Google Lens, Wikipedia
Description: Find the DOI of this image.
Flag: SWIMMER{10.11501/967480}
Write-up
Reverse image search identified the design as Watanabe Fukuzo’s entry for the National Diet Building competition.
Source: https://dl.ndl.go.jp/pid/967480/1/7
The DOI shown in the archival metadata: 10.11501/967480
rain_05_date
Tools: Google, LinkedIn, Image Analysis
Description: Find the date when this picture was captured.
Flag: SWIMMER{2025/12/07}
Write-up
I identified the green banner as:
SUNTORY 10000 Freude Beethoven’s 9th
Searching Google, found a helpful LinkedIn post: https://www.linkedin.com/posts/suntory-holdings-limited_suntory10000freude-givingbacktosociety-activity-7404981711249408000-KAj6
This confirmed the event occurred on 7 December 2025.
Conclusion
This CTF heavily favored Japanese-language OSINT and media tracing. It significantly improved my skills in:
- event correlation
- video-based geo-location
- archival document analysis
- multilingual OSINT
We didn’t place at the top, but I did learn a lot.
Plus Ultra.