kashiCTF 2026 - Conquer

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I like to save my files as pdfs. Kashi kings hate 184.

Initial Analysis

The file is named flag.pdf, but standard PDF analysis tools fail to recognize it:

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pdfid flag.pdf
# Output: Not a PDF document

Using the file command reveals its true identity:

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file flag.pdf
# Output: flag.pdf: Netpbm image data, size = 284 x 150, rawbits, pixmap

The challenge hint “Kashi kings hate 184” suggests that the height of the image (currently 150) has been tampered with and should likely be 184.

Extraction & Decoding

Netpbm (PPM) files use a plain-text header. We can repair the height by editing the file header. Opening the file in a hex editor or a text editor like vim (using :set binary or simply editing the ASCII header) reveals:

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P6
284 150
255
[Binary Data...]

Change the height value from 150 to 184:

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P6
284 184
255
[Binary Data...]

After saving the change, the image can be opened with a standard image viewer to reveal the flag.

Flag

kashiCTF{iLOVEkashi}