Disk, disk, sleuth! II

Problem

All we know is the file with the flag is named down-at-the-bottom.txt... Disk image: dds2-alpine.flag.img.gz

• dds2-alpine.flag.img.gz

Solution

1. Using the TSK Tool Overview website we can find that the fls command can list all files in a directory. We specify the -r, which means recursive so it will scan the entire disk image, and -p, so it prints the full path, flags. The -o flag is the offset of the partition we want to use, which can be dounf by running mmls dds2-alpine.flag.img. Finally, we search the output using grep for the name of the file given in the challenge description. So, the resulting command looks as follows: fls -r -p -o 2048 dds2-alpine.flag.img | grep down-at-the-bottom.txt. The output is: r/r 18291: root/down-at-the-bottom.txt

2. 18291 is the inode number of the file. We can use icat to list the contents of that inode like so: icat -o 2048 dds2-alpine.flag.img 18291

   The flag is shown in the output (inside of a unique pattern so we couldn't simply search for it):

     _     _     _     _     _     _     _     _     _     _     _     _     _  
    / \   / \   / \   / \   / \   / \   / \   / \   / \   / \   / \   / \   / \ 
   ( p ) ( i ) ( c ) ( o ) ( C ) ( T ) ( F ) ( { ) ( f ) ( 0 ) ( r ) ( 3 ) ( n )
    \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/ 
     _     _     _     _     _     _     _     _     _     _     _     _     _  
    / \   / \   / \   / \   / \   / \   / \   / \   / \   / \   / \   / \   / \ 
   ( s ) ( 1 ) ( c ) ( 4 ) ( t ) ( 0 ) ( r ) ( _ ) ( n ) ( 0 ) ( v ) ( 1 ) ( c )
    \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/ 
     _     _     _     _     _     _     _     _     _     _     _  
    / \   / \   / \   / \   / \   / \   / \   / \   / \   / \   / \ 
   ( 3 ) ( _ ) ( 0 ) ( b ) ( a ) ( 8 ) ( d ) ( 0 ) ( 2 ) ( d ) ( } )
    \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/   \_/ 

3. Alternatively, autopsy can be used to interact with the disk in a GUI, which may be easier. It was easier for me at at first.

Flag

picoCTF{f0r3ns1c4t0r_n0v1c3_0ba8d02d}