Graded Reels CTF Challenge Writeup

Challenge Information

• Name: Graded Reels
• Points: 150
• Category: Forensics
• Objective: Analyze an image with a partially hidden flag by manipulating its properties.

Solution

To solve the “Graded Reels” challenge, follow these steps:

1. Initial Inspection:

   • Open the provided image. At first glance, it seems like the flag is partially cut off at the bottom.

2. Using Online Tools:

   • Attempt to use tools like FotoForensics to reveal any hidden or manipulated pixels at the bottom of the image.

   • Unfortunately, FotoForensics does not clearly display the hidden portion of the flag, which means you will need to manually modify the image.

     

3. Manual Image Manipulation:

   • Use ExifTool to extract the metadata of the image, including its height.

   • Once you find the height value in the metadata, convert this value from decimal to hexadecimal.

     

     

4. Hex Editing:

   • Open the image file in HexEdit (or any hex editor).

   • Locate the height value in the hex editor by searching for the hexadecimal representation of the height you found earlier.

     

5. Modify the Image’s Height:

   • Increase the height of the image by modifying the corresponding value in the hex editor.
   • After increasing the value, save the changes to the image file.

6. Reveal the Flag:

   • Open the modified image, and you should now be able to see the previously hidden portion of the image, revealing the complete flag.