PowerShell actually makes this amazingly easy, allowing commands of the form:
The executable can be decoded and saved to disk by passing the -dump switch. The obvious one is Base64 encoding, but other encoding techiques (gzip, XOR, etc), string techniques (escaping, format string, concat, etc. Just download it and add it to metasploit folder. So, the first thing is that we need to create encoder and add it in metasploit folder. The trick that is used in this case is using environment variables that holds a string. The IEX can be used to run a one liner command that can perform execution of remote malicious script.In order to understanding the common PowerShell one liner exploits that use IEX cmdlet, we will check the following example:The above command will download (into the PS memory) an expression from the given URL and execute it via IEX cmdlet, which means that the cybad.ps1 script context will be executed from the PowerShell virtual memory and not from the disk. Deobfuscating the PowerShell script Decoding the Base64-string we got from the document’s comment field, we find some slightly obfuscated PowerShell code: PowerShell has built-in functionality to save sensitive plaintext data to an encrypted object called If you are a threat hunter, you will be well familiar with PowerShell and common obfuscation techniques. The formatting operator (-f) is dividing the string into several parts and it will reorder them by the curly bracket’s numbers.So, if we combine these two strings, the result is ‘IEX’So now when we know how to deal with the formatting operator (-f), we can check for the next bracket and so on.This command uses classes to convert a base64 encoded string to a memory stream. By using So far, great, you might think. Here is the link for encoder created in ruby. First of all it is obvious that the payload command it base64 encoded by either looking at the format or by the -encodedcommand PowerShell flag. Remember we need to find the IEX and delete it.The first pattern that we can figure is that the obfuscation script is split by brackets ().The second pattern is the curly brackets {} that hold numbers:This is the known obfuscation technique that is called “Reordering”. Encoded PowerShell attacks on Windows. In the last episode of "Ryan's Tall Tales of PowerShells," I discussed my single favorite method to log PowerShell activity.Today, we shall talk about some methods to hunt the PowerShells. For now, direct use of .NET is needed. The only limitation is a 65,536 character limit on the original text. Added Base64 encoded executable detection and extraction functionality. In my research for our "Hunting the Known Unknowns" presentation at .conf2016, I mentally broke malicious PowerShell toolsets into two methodologies: collection of scripts and agent based.
However, as is the case for most of PowerShell’s functionality, for each good, legit use case there is at least one bad, malicious use case.Next to classic obfuscation techniques such as Base64 encoding, XOR encoding, escaping, etc., Deserialising the above output and turning it back into plaintext can be achieved as follows:This is not the only method that works, other techniques are available:As a result, an attacker can, similar to the traditional Base64 encoding, decode their data using a one-liner, with the benefit of the payload being AES encrypted. part and keep the rest. ), downloading & executing in memory are just a few other ways that might help attackers stay under the radar.
Function – Ndmorrswify. If you are a threat hunter, you will be well familiar with PowerShell and common obfuscation techniques. ), downloading & executing in memory are just a few other ways that might help attackers stay under the radar. In this case the $SHeLLid is the environment variable that is used.So, this variable holds the following string of ‘Microsoft.PowerShell’.The Square brackets ‘[]’ hold the index number of the sliced string from the variable.In this way it will combine the IEX cmdlet, I + E + X = IEX.Afterwards, we have found the IEX, and we can delete it and run the first part of the command in order to decompress the compression and decode the base64 command.In the following snap you will be able to see the result of the script:Sign up to get the latest news and developments in endpoint and network security, and Cynet.
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