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Raymonds Recovery [forensics]

solved by skat

Writeup by not_really

Uh-oh! Someone corrupted all my important files and now I can’t open any of them. I really need one of them in particular, a png of something very important. Please help me recover it!

Here, take this ext4 filesystem and see what you can find. If you can figure out which file it is and how to fix it, you’ll get something in return!

Files: raymonds_fs

This one is easy. To extract the file system, you can use 7-zip on windows or

mkdir raymonds_fs_out; sudo mount -o loop raymonds_fs raymonds_fs_out on linux.

The hint suggests that we’re looking for a png, so let’s look at the headers.

for file in *; do echo $file; xxd $file | head -1; done will look at the top bytes of each file in the folder. For each file, it prints the filename and uses xxd to print the hex with head -1 to print only the first line.

7e8bc0dde7339e79edf3a1627ce76b50
00000000: e000 104a 4649 4600 0101 0200 1c00 1c00  ...JFIF.........
also_not_the_flag
00000000: e000 104a 4649 4600 0101 0100 6000 6000  ...JFIF.....`.`.
another_nice_drawing
00000000: e000 104a 4649 4600 0101 0000 0100 0100  ...JFIF.........
art_at_its_finest
00000000: e000 104a 4649 4600 0101 0000 0100 0100  ...JFIF.........
blathers
00000000: 0000 104a 4649 4600 0101 0000 0100 0100  ...JFIF.........
cool_hat
00000000: ffd8 ffe0 0010 4a46 4946 0001 0101 015e  ......JFIF.....^
definitely_not_the_flag
00000000: 2d31 2e33 0a25 c4e5 f2e5 eba7 f3a0 d0c4  -1.3.%..........
even_more_fanart
00000000: db00 4300 0806 0607 0605 0807 0707 0909  ..C.............
even_MORE_fancy
00000000: ffd8 ffdb 0043 0006 0405 0605 0406 0605  .....C..........
fanart
00000000: e000 104a 4649 4600 0101 0000 0100 0100  ...JFIF.........
fancy_shoes
00000000: ffd8 ffe0 0010 4a46 4946 0001 0101 0048  ......JFIF.....H
fos6fy0qcbq41
00000000: e000 104a 4649 4600 0101 0000 0100 0100  ...JFIF.........
gift_from_judy
00000000: e000 104a 4649 4600 0101 0000 0100 0100  ...JFIF.........
goals
00000000: e000 104a 4649 4600 0101 0100 6000 6000  ...JFIF.....`.`.
great_design
00000000: 2d31 2e33 0d0a 25e2 e3cf d30d 0a0d 0a31  -1.3..%........1
I_love_my_fans
00000000: e000 104a 4649 4600 0101 0000 0100 0100  ...JFIF.........
lost+found
xxd: Is a directory
might_be_the_flag_but_you_dont_know
00000000: 2d31 2e33 0a25 c4e5 f2e5 eba7 f3a0 d0c4  -1.3.%..........
more_fanart
00000000: e000 104a 4649 4600 0101 0100 4800 4800  ...JFIF.....H.H.
more_hats
00000000: ffd8 ffe0 0010 4a46 4946 0001 0101 0060  ......JFIF.....`
my_fav_art
00000000: 0000 000d 4948 4452 0000 0280 0000 0280  ....IHDR........
office_art
00000000: e000 104a 4649 4600 0101 0101 2c01 2c00  ...JFIF.....,.,.
office_supplies_art
00000000: e000 104a 4649 4600 0101 0000 0100 0100  ...JFIF.........
read_later
00000000: 2d31 2e33 0a25 c4e5 f2e5 eba7 f3a0 d0c4  -1.3.%..........
really_important
00000000: e000 104a 4649 4600 0101 0000 0100 0100  ...JFIF.........
self_portrait
00000000: e000 104a 4649 4600 0101 0000 0100 0100  ...JFIF.........
style_inspo
00000000: e000 104a 4649 4600 0101 0101 2c01 2c00  ...JFIF.....,.,.
very_important_records
00000000: 2d31 2e33 0a25 c4e5 f2e5 eba7 f3a0 d0c4  -1.3.%..........

JFIF is a jpeg, so we can cross those off the list.

definitely_not_the_flag
00000000: 2d31 2e33 0a25 c4e5 f2e5 eba7 f3a0 d0c4  -1.3.%..........
even_more_fanart
00000000: db00 4300 0806 0607 0605 0807 0707 0909  ..C.............
even_MORE_fancy
00000000: ffd8 ffdb 0043 0006 0405 0605 0406 0605  .....C..........
great_design
00000000: 2d31 2e33 0d0a 25e2 e3cf d30d 0a0d 0a31  -1.3..%........1
might_be_the_flag_but_you_dont_know
00000000: 2d31 2e33 0a25 c4e5 f2e5 eba7 f3a0 d0c4  -1.3.%..........
my_fav_art
00000000: 0000 000d 4948 4452 0000 0280 0000 0280  ....IHDR........
read_later
00000000: 2d31 2e33 0a25 c4e5 f2e5 eba7 f3a0 d0c4  -1.3.%..........
very_important_records
00000000: 2d31 2e33 0a25 c4e5 f2e5 eba7 f3a0 d0c4  -1.3.%..........

Aha, we see IHDR, but it doesn’t have the PNG magic. Let’s see what the image looks like right now.

image-20200721204648751

And then we can open any other png we have lying around to see what it looks like.

image-20200721204823436

Aha, this image has eight extra bytes that my_fav_art doesn’t have. Let’s copy them and put them into my_fav_art.

image-20200721204731703

After renaming it to .png we get this.

image-20200721205012522