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ctf-notes/steganography/exif-thumbnail/notes.org
Tuan-Dat Tran de45645553 webserver 
Signed-off-by: Tuan-Dat Tran <tuan-dat.tran@dextradata.com>
2026-03-21 14:33:49 +01:00

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EXIF - Thumbnail

Task

Find the password hidden in this JPG image.

./ch10.jpg

exiftool ch10.jpg -b > thumbnail.bin

Full process

  1. Checked metadata in the original image:
exiftool ch10.jpg

Key findings:

  • `Thumbnail Offset: 202`
  • `Thumbnail Length: 41506`
  1. Extracted the correct thumbnail from EXIF:
exiftool -b -ThumbnailImage ch10.jpg > thumb_extracted.jpg
file thumb_extracted.jpg
exiftool thumb_extracted.jpg

Result:

  • `thumb_extracted.jpg` is a valid JPEG (600x339)
  • it also contains another EXIF thumbnail (`Thumbnail Length: 15957`)
  1. Extracted one level deeper:
exiftool -b -ThumbnailImage thumb_extracted.jpg > thumb2.jpg
file thumb2.jpg
exiftool thumb2.jpg

Result:

  • `thumb2.jpg` is a JPEG (300x300)
  • JPEG comment: `We need to go deeper`
  1. Extra checks (stego tools unavailable in this environment):
steghide info thumb2.jpg
binwalk thumb2.jpg

Both commands were not installed in this environment.

  1. Opened/read the image content of `thumb2.jpg` directly.

The text visible in the image:

`The flag is: B33r!sG00d!`

Flag

`B33r!sG00d!`