![crypter stub crypter stub](http://2.bp.blogspot.com/-0CPrdLpVZqw/UIAVqNAUPtI/AAAAAAAAAOQ/pmptxDqLFx8/s1600/iRMy8QIaTXR3u.png)
In any case, for the purposes of this POC, I saved myself an enormous amount of time by slightly modifying this repository from Github, which has reliable and stable build that accomplishes the task of the system EXE loader and executes an executable from its own address space.
Crypter stub code#
Reading code projects and examples are also very useful.
Crypter stub how to#
To learn about the Microsoft Portable Executable (PE) format and how to load compiled executables into memory yourself, I recommend starting with the specification and other resources from Microsoft, OpenSecurityTraining and Joachim Bauch. On windows, the system EXE loader maps sections of an executable into memory, performs some address relocation fix-ups if necessary, and then resolves imports by loading the addresses of included functions into the executables memory so it can actually make use of imported functions.
Crypter stub windows#
In either case, the stub generally must be able to parse the windows executable format data structure (PE) and perform the task of the system EXE (PE) loader. To accomplish this, techniques such as Process Hollowing or running the decrypted program entirely from within the stub’s own address space may be used. To create a runtime crypter for Windows, the stub program must be able to take an encrypted executable image, reverse the encryption, and then hand control of execution over to the decrypted executable. For this reason, the terms packer and crypter are often used synonymously. Because runtime crypters must be able to extract and execute a binary image on their own, they employ techniques similar to those found in self-extracting archives, and even more closely to packers - programs which take compressed or archived binary files and execute them as if they were the original. This allows runtime crypters to evade antivirus signature detection – antivirus must use other means to defend against such protected malware, such as heuristic analysis or behavioral detection. This generally includes decrypting the original, and then executing the now decrypted binary image directly from memory, performing the tasks generally performed by the OS executable loader when executing a program.
![crypter stub crypter stub](http://1.bp.blogspot.com/-5xzcqNagUWs/U1u_BzGjJYI/AAAAAAAABXs/t04gqZnCWCk/s1600/17%252Bcifrando%252Bmalware.png)
A stub program containing the original, but obfuscated, executable file (often malware) within its data performs staging to prepare the embedded, obfuscated code for execution. Runtime crypters, on the other hand, do not write anything to disk. As soon as the file is unencrypted and written to disk, it should be detected and quarantined by any decent modern antivirus. Scantime crypters generally evade detection from antivirus scanning until execution. Scantime crypters take an encrypted executable and reverse the encryption, and then write this executable to disk and execute it from there. Crypters may be divided into two categories: scantime and runtime.
Crypter stub software#
“Crypter” generally refers to software used by hackers and security researchers to conceal malware, particularly when infecting a victim’s computer. The below code is from this GitHub fork: Background Because the unencrypted binary executed from the stub.exe program never touches disk, it may be used to conceal programs from signature based detection systems employed by antivirus software. The second, stub.exe, takes this encrypted executable stored within itself as a resource, decrypts it and then executes it from memory. The first program, crypter.exe, is designed to obfuscate an executable file using a simple XOR encryption algorithm. The following project is separated into two separate components.
![crypter stub crypter stub](https://i.ytimg.com/vi/R0LOqZB5glM/maxresdefault.jpg)
![crypter stub crypter stub](https://i.ytimg.com/vi/Q2XFLxzDc5s/hqdefault.jpg)
The following is a very simple example of a crypter written in C++.