It supports Windows XP and higher. The IDAT chunk contains the actual image data, which is the output stream of the compression algorithm. It's in this chunk that we'll store the PHP shell. chunk IDAT at offset 0x150008, length 45027 chunk IDAT at offset 0x15aff7, length 138 chunk IEND at offset 0x15b08d, length 0 No errors detected in sctf.png (28 chunks, 36.8% compression). Interlacd PNG are encoded in a way that the users feel the the image is loaded faster. At least one 'fdAT' chunk is required for each frame. PNG:CreationTime may not show up properly when written by exiftool. If you're curious about the filtering and compression on PNG images check out Filtering and Compression. The four-byte chunk type field contains the decimal values 73 68 65 84. The 'fdAT' chunk has the same purpose as an 'IDAT' chunk. Within the PNG file format (we’ll focus on true-color PNG files rather than indexed) the IDAT chunk stores the pixel information. See this Exiftool Forum post. A valid PNG image must contain an IHDR chunk, one or more IDAT chunks, and an IEND chunk. PNG file format basics. IDAT chunk can be split into multiple chunks. After reading fin1te’s post on “An XSS on Facebook via PNGs & Wonky Content Types“, and idontplaydarts’ post on “Encoding Web Shells in PNG IDAT chunks“, I figured it would be useful to create my own. See Summary of standard chunks in PNG Specification. Compression. IDAT contains the image, which may be split among multiple IDAT chunks. For now we'll assume that pixels are always stored as 3 bytes representing the RGB color channels. The IDAT Chunk . The IDAT chunk contains the actual image data which is the output stream of the compression algorithm. Such splitting increases filesize slightly, but makes it possible to generate a PNG in a streaming manner. For now we’ll assume that pixels are always stored as 3 bytes representing the RGB color channels. PNG file format basics. If you have a particular PNG chunk type in mind, you can look here to see what support PyPNG provides for it. TweakPNG is a low-level utility for examining and modifying PNG image files. There are 4 kinds of critical chunk and 14 kinds of ancillary chunk. So when we should wait till we meet IEND chunk before we decode the IDAT chunk. Within the PNG file format (we'll focus on true-color PNG files rather than indexed) the IDAT chunk stores the pixel information. It’s in this chunk that we’ll store the PHP shell. This document is intended to help users who are interested in a particular PNG chunk type. It has the same structure as an 'IDAT' chunk, except preceded by a sequence number. The compressed datastream is then the concatenation of the contents of the data fields of all the 'fdAT' chunks within a frame. PNG compression method 0 (the only compression method presently defined for PNG) specifies deflate/inflate compression with a sliding window of at most 32768 bytes. 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