![]() ![]() The first few hundred bytes of the typical PE file are taken up by the MS-DOS stub. The header contains info such as the location and size of code, as we discussed earlier. Like other executable files, a PE file has a collection of fields that defines what the rest of file looks like. The address F8000000 and the offset at the address 000000F8, where the PE starts, means the offset to the PE address and that is at the 0x00000030 address. This file is kept in the address 0x3c, which is offset to the next PE header section. When building applications on Windows, the linker sends instruction to a binary called winstub.exe to the executable file. The DOS stub usually just prints a string, something like the message, “This program cannot be run in DOS mode.” It can be a full-blown DOS program. The windows loader looks for this offset so it can skip the DOS stub and go directly to the PE header. Ifanew is the only required element (besides the signature) of the DOS HEADER to turn the EXE into a PE. Here, using CFF, explorer we can verify the offset value of the structure and DOS MZ header and we also see that the file has the data type WORD. We can see above that we have list of structure for Image_DOS_Header and the important header, as we already discussed This one is developed by Mark Zbikowski (MZ) It starts at offset 0 (this can be view with a hex editor). ![]() MS-DOS headers are sometimes referred to as MZ headers for this reason. All MS-DOS-compatible executable files set this value to 0x54AD, which represents the ASCII characters MZ. This field is used to identify an MS-DOS-compatible file type. The first field, e_ magic, is the so-called magic number. We will not discuss everything as it is beyond our scope we will discuss important ones that are required, such as magic and ifanew structure. We also have a same implementation as a pictureĪs we can see we have a list of structure that came under DOS header. Same thing can be found on the cff-explorer which is very popular malware analysis tool for PE file validation. As we can investigate on the winnt.h/Windows.inc we can see below details: ![]() It’s there because DOS can recognize it as a valid executable and can run it in the DOS stub mode. The diagram below explains everythingĭOS header starts with the first 64 bytes of every PE file. A PE executable basically contains two sections, which can be subdivided into several sections.
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