![]() ![]() IMO this is not really a security problem with UnZip. Info-ZIP UnZip 6.0 mishandles the overlapping of files inside a ZIP container, leading to denial of service (resource consumption), aka a "better zip bomb" issue. Optimization (balance of kernel size vs.Local file headers are treated as both code and data:Īnd as part of a DEFLATE stream (file data). LEN is the number of data bytes in the block. The rest of the block consists of the following information: Thus making it a valid part of the DEFLATE stream.Įach block of compressed data begins with 3 header bitsīFINAL is set if and only if this is the last block of the dataīTYPE specifies how the data are compressed, as follows:ġ0 - compressed with dynamic Huffman codesĪny bits of input up to the next byte boundary are ignored. Solution: add a prefix that wraps the local file header To prevent them from being interpreted as DEFLATE data. (See overlap.zip, generated by the source code.) You will quickly think of many troubling questions. The zip file format specification is calledįor a specification, it's not very precise. The headers in the central directory and in theįiles contain (redundant) metadata such as the filename. Which is like a table of contents that points backwards Goal: high compression ratio without using recursion.Ī zip file consists of a central directory, Tries to work around the DEFLATE limitation $ dd if=/dev/zero bs=1000000 count=1000 | gzip > test.gzĬompressed uncompressed ratio uncompressed_name The only universally supported compression algorithm isīut DEFLATE's maximum compression ratio is 1032. Haven't I heard this before? Limits of the DEFLATE compression algorithm $ time unzip -p zblg.zip | dd bs=32M of=/dev/null status=progress. $ wc -bytes zbsm.zip zblg.zip zbxl.zip 42374 zbsm.zip ![]() Source code / short demo source code link ![]() LHA or LZH is a freeware compression utility and associated file format.A better zip bomb (dc303 talk) A better zip bomb It was created in 1988 by Haruyasu Yoshizaki ( 吉崎栄泰, Yoshizaki Haruyasu), and originally named LHarc. A complete rewrite of LHarc, tentatively named LHx, was eventually released as LH. It was then renamed to LHA to avoid conflicting with the then-new MS-DOS 5.0 LH ("load high") command. According to early documentation, LHA is pronounced like La.Īlthough no longer much used in the West, LHA remains popular in Japan. It was used by id Software to compress installation files for their earlier games, including Doom and Quake. LHA has been ported to many operating systems and is still the main archiving format used on the Amiga computer, although it competed with LZX in the mid 1990s. This was due to Aminet, the world's largest archive of Amiga-related software and files, standardising on Stefan Boberg's implementation of LHA for the Amiga. Microsoft has released a Windows XP add-on, Microsoft Compressed (LZH) Folder Add-on, designed for the Japanese version of the operating system. The Japanese version of Windows 7 ships with the LZH folder add-on built-in. Users of non-Japanese versions of Windows 7 Enterprise and Ultimate can also install the LZH folder add-on by installing the optional Japanese language pack from Windows Update. In an LZH archive, the compression method is stored as a five-byte text string, e.g. These are the third through seventh bytes of the file. ![]()
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