$ cat writeup.md…
$ cat writeup.md…
fortid2026
Task: no files, only a hint that a flag from the previous CTF edition is 'still around'. Solution: OSINT pivot to the organizers' 2025 blog post reveals a hidden flag, then a PNG height-truncation stego trick — the IHDR under-declares height so extra scanlines are decoded and unfiltered to reveal the flag text.
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If you stumbled upon one of our flags after last year's contest, now is the time to submit it. If not, I guess you'll just have to use your skills and find it, it should still be around... 👀
No files were provided. The challenge points at the previous edition of the CTF and claims the flag is "still around", with the same 👀 emoji the organizers used in their 2025 wrap-up. The goal is to find a flag hidden somewhere online since last year's event.
Two distinct phases: an OSINT pivot to locate the hiding place, and a PNG forensics trick to extract the actual flag.
OSINT pivot (previous edition → organizers' blog):
FortID{} and the "last year's contest" wording point to FortID CTF 2025, run by TBTL / Blockhouse Technology Zagreb.lnkd.in short link) to a blog post.https://fortid.com/blog/fortid-ctf-2025/....
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