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0 pointsguessmyname2y ago0 comments

> I wouldn't even know how to look for something unusual in a gif's source code but I also feel this is the most compelling part. I wish they'd uploaded it.

GIF stands out as a widely understood file format [1][2].

To kick things off, delve into the GIF file using a hexadecimal editor. HexFiend [3], for instance, offers a template for visualizing GIF file structures [4]. Another excellent option is Synalyze It! [5], which comes pre-loaded with an extensive list of file formats, encompassing GIF among others.

These visualizations serve as a guide to pinpoint any irregular byte clusters that might pose issues when loading the file into an application with an image reader lacking support for that specific byte group or its arrangement. Once you've identified such a cluster, consider it the bug.

[1] https://en.wikipedia.org/wiki/GIF#Example_GIF_file

[2] https://www.w3.org/Graphics/GIF/spec-gif89a.txt

[3] http://hexfiend.com

[4] https://github.com/HexFiend/HexFiend/blob/master/templates/I...

[5] https://www.synalysis.net

0 comments

spuz2y ago

Another good option is ImHex which is an open source hex editor that supports file patterns. The gif pattern is one of the patterns already available:

https://github.com/WerWolv/ImHex

tchebb2y ago

Kaitai Struct[1] is my preferred tool for parsing binary files. It's open-source (unlike Synalize It! and 010 Editor) and cross-platform (unlike HexFiend). Not sure how it compares to ImHex's pattern language, though—I've been put off by ImHex's UI the few times I've tried it.

My favorite thing about the Kaitai Web IDE is that it instantly updates the parsed tree as you make changes to the format specification, which makes it viable for reversing unknown formats instead of just specifying known ones.

[1] https://ide.kaitai.io/

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