![]() Later on, the FUD payload will be parsed from a STUB program in order to decrypt it and execute it on runtime.Īfter the short introduction above, it is time for me to start the practical demonstration and proof of concept regarding the use of a fully undetectable cryptor, to evade the AV engine in Kaspersky Endpoint Security software. At this point it is worth mentioning that there is no need to use a complicated algorithm such as AES to encrypt the payload, because satisfying results can also be achieved using lightweight encryption. Furthermore, the encryption algorithm used in this example is the Affine cipher. ![]() The bind shell will be encrypted using a FUD Cryptor. Therefore, the results could provide a high probability rate in malware detection.įor this exercise we will be using a bind shell generated from metasploit framework. Specifically, the malicious code is executed and self-decrypted in AV sandbox, and from the final analysis of the code, any possible suspicious behaviour will be flagged as malicious from the AV engine. Furthermore, combining the results from dynamic analysis along with signature verification and heuristic analysis, allows the detection of unknown malware as well as those relying on encryption. Moreover, regarding the use of dynamic analysis, a malicious executable is scanned and launched in a virtual environment for a short amount of time. Both static and dynamic analysis providing very satisfying detection results making the development of malicious software hard. These days most Antivirus engines rely mostly on dynamic analysis rather on static analysis only. The main purpose of FUD Cryptors is to obfuscate the contents of a malicious executable in order to make the executable undetectable to antivirus software without interfering with the intended execution flow of the executable. This post presents a way to evade Antivirus products using a FUD Cryptor.
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