![]() ![]() Cybercriminals can use it to protect any malware that they want to deliver. For example, it allows the configuration of the encryption method and key as well as where the payload should be injected.Īs you can see, a crypter is a completely independent module. That's why authors provide a GUI to configure all the options in a very easy way. These products are designed to cater to simple criminals, those who do not need (or want) a deep technical knowledge. Below, you can see examples of crypters being advertised on the black market and the tricks they use: Underground crypters, created to defend malware against antivirus/anti-malware products, are sold in typical cybercriminal hangouts. They may also add some icons and metadata that make the sample look like a legitimate product. They try to deceive pattern-based or even behavior-based detection engines - often slowing down the analysis process by masquerading as a harmless program then unpacking/decrypting their malicious payload. A crypter's role is basically to be the first - and most complex - layer of defense for the malicious core. Most modern malware samples, in addition to built-in defensive techniques, are protected by some packer or crypter. We will also present some example of identifying and unpacking a malware crypter. ![]() Today, we will study some examples to make sure that everyone knows what this type of tools are and why they are dangerous. However, additional evasion techniques may be implemented in future releases to improve the baseline design.Recently, two suspects were arrested for selling Cryptex Reborn and other FUD tools (helping to install malware in a Fully UnDetectable way). If you want PEunion to be FUD, please get familiar with the code of the stub and adjust it until you are satisfied with the result. ![]() Rather, PEunion offers a fully functional implementation that is easy to modify and extend. Therefore, there will be no updates to fix detection issues. Adjusting the stub so it does not get detected is a daunting task and all efforts are in vain several days later. A crypter that is free, publicly available, and open source will not remain undetected for a long time. This project is FUD on the day of release. I do not take any responsibility for anybody who uses PEunion in illegal malware campaigns. Have a basic understanding of in-memory execution and evasion techniquesĪcknowledge that uploading the stub to VirusTotal will decrease the time that the stub remains FUD In order to use this program, you should:īe familiar with crypters and the basic concept of what a crypter does This way, an executable can be crafted in such a way that it looks like a JPEG file. It is a simple renaming technique, where all characters followed by U+202e are displayed in reversed order. The Unicode character U+202e allows to create a filename that masquerades the actual extension of a file. Both string and integer literals are decrypted at runtime. The C# obfuscator replaces symbol names with barely distinguishable Unicode characters. Strings are not stored in the data section, but instead constructed on the stack using mov-opcodes. Hence, AV detection is limited to the stub itself.Īssembly code is obfuscated by nop-like instructions intermingled with the actual code, such as an increment followed by a decrement. Because the resulting data has no repeating patterns, it is impossible to identify this particular encoding and infer YARA rules from it. To decrease entropy, the encrypted shellcode is intermingled with null-bytes at randomized offsets. The shellcode is encrypted using a proprietary 4-byte XOR stream cipher. Stage 2 contains all the “suspicious” code that is not readable at scantime and not decrypted, if an emulator is detected. To mitigate AV detections, only the stub requires adjustments. The second stage is position independent shellcode that retrieves function pointers from the PEB and handles the payload. The fundamental concept is that the stub only contains code to detect emulators and to decrypt and pass execution to the next layer. This graph illustrates the execution flow of the native stub decrypting and executing a PE file. The exact implementation is fine tuned to decrease detection and is subject to change in future releases. Obfuscation and evasive features are fundamental to the design of PEunion and do not need further configuration. Legitimate files with no known signatures can be written to the disk. If the executable is a native PE file, RunPE (process hollowing) is used. ![]() Typically, an executable is decrypted and executed in-memory by the stub. A file can either be embedded within the compiled executable, or the stub downloads the file at runtime. Multiple files can be compiled into the stub. Specify icon, version information & manifest Two stubs are available to choose from, both of which work in a similar way.Native: Written in assembly (FASM) ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |