Instagram Writeup

TAMUctf 2020 - Misc 50

Fix JPEG file

Similar writeup: SECCON CTF 2017: JPEG File. My goal is to fix jpeg marker. To detect JPEG error, I used gimp. Locate error by observing the output of gimp, such as:

(gimp:27558): GLib-GObject-WARNING **: 23:55:03.929: g_object_set_is_valid_property: object class 'GeglConfig' has no property named 'cache-size'
JPEG image-Warning: Corrupt JPEG data: 1602 extraneous bytes before marker 0xfe

JPEG image-Warning: JPEG datastream contains no image

GIMP-Error: Opening failed: JPEG image plug-In could not open image

Use vim with xxd to patch each marker error. vim -b binaryfile, :%!xxd, :%!xxd -r. After five attempts, I get readable image and get flag:

gigem{cH4nG3_the_f0rMaTxD}

Original broken image: photo.jpg

Result of trials to get readable image: photo2.jpg, photo3.jpg, photo4.jpg

Final output: photo5.jpg

Original writeup (https://github.com/pcw109550/write-up/tree/master/2020/TAMUctf/INSTAGRAM).