The Zip Bomb

Files so deeply compressed that they’re effectively malware have been around for decades—and a researcher just unveiled a brand-new Zip bomb that explodes a 46-megabyte file to 4.5 petabytes of data

In the roughly three decades since the Zip file format debuted, compressed files have been subject to widespread use—and occasional misuse.

Certainly, what programmer and engineer David Fifield recently did with the Zip file format fits in the latter category. Effectively, Fifield invented a new type of “Zip bomb” or “compression bomb” — a malware variant in which a Zip file as small as a few kilobytes is so compressed it would completely fill up your hard drive when decompressed. And then some.

Files like these aren’t unheard-of, but Fifield’s techniques, revealed in an article on his website, are particularly novel because they aren’t “recursive,” or built like an inverted Russian nesting doll where the files get bigger as you decompress multiple layers of Zip files. Instead, Fifield figured out how to “overlap” files inside of a Zip archive, allowing for compression rates far beyond those of a traditional archive—in his most impressive case, he managed to get a 46-megabyte file to compress 4.5 petabytes of data.

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