Author: Marin Radu
Manipulate the height of an image with from the specific bytes
- Image analysis
Check this blog post that explains how to modify the height (and width) of an JPG image.
In short, just look for the sequence of hex characters ff c0; the next 4 bytes resemble the length, the next 2 are the data precision, then we have 4 bytes for image height and 4 more for image width.
This image contains the following sequence of bytes: ff c0, 00 11, 08, 03 2e, 04 2e.
I used Hexeditor to 'crop' the image and leave out the flag from the lower part of the image.
- Search for the relevant bytes in hex format
- Modify them to reveal the flag (replace
08 03 2ewith08 04 2e)
Flag:
CSCTF{h1dden_pixels_f0r_you}