Dynmx - Signature-based Detection Of Malware Features Based On Windows API Call Sequences

dynmx (spoken dynamics) is a signature-based detection approach for behavioural malware features based on Windows API call sequences. In a simplified way, you can think of dynmx as a sort of YARA for API call traces (so called function logs) originating from malware sandboxes. Hence, the data basis for the detection approach are not the malware samples themselves which are analyzed statically but data that is generated during a dynamic analysis of the malware sample in a malware sandbox. Currently, dynmx supports function logs of the following malware sandboxes:

• VMRay (function log, text-based and XML format)
• CAPEv2 (report.json file)
• Cuckoo (report.json file)

The detection approach is described in detail in the master thesis Signature-Based Detection of Behavioural Malware Features with Windows API Calls. This project is the prototype implementation of this approach and was developed in the course of the master thesis. The signatures are manually defined by malware analysts in the dynmx signature DSL and can be detected in function logs with the help of this tool. Features and syntax of the dynmx signature DSL can also be found in the master thesis. Furthermore, you can find sample dynmx signatures in the repository dynmx-signatures. In addition to detecting malware features based on API calls, dynmx can extract OS resources that are used by the malware (a so called Access Activity Model). These resources are extracted by examining the API calls and reconstructing operations on OS resources. Currently, OS resources of the categories filesystem, registry and network are considered in the model.

Example

In the following section, examples are shown for the detection of malware features and for the extraction of resources.

Detection

For this example, we choose the malware sample with the SHA-256 hash sum c0832b1008aa0fc828654f9762e37bda019080cbdd92bd2453a05cfb3b79abb3. According to MalwareBazaar, the sample belongs to the malware family Amadey. There is a public VMRay analysis report of this sample available which also provides the function log traced by VMRay. This function log will be our data basis which we will use for the detection.

If we would like to know if the malware sample uses an injection technique called Process Hollowing, we can try to detect the following dynmx signature in the function log.

dynmx_signature:
  meta:
    name: process_hollow
    title: Process Hollowing
    description: Detection of Process hollowing malware feature
  detection:
    proc_hollow:
      # Create legit process in suspended mode
      - api_call: ["CreateProcess[AW]", "CreateProcessInternal[AW]"]
        with:
          - argument: "dwCreationFlags"
            operation: "flag is set"
            value: 0x4
          - return_value: "return"
            operation: "is not"
            value: 0
        store:
          - name: "hProcess"
            as: "proc_handle"
          - name: "hThread"
            as: "thread_handle"
      # Injection of malicious code into memory of previously created process
      - variant:
        - path:
          # Allocate memory with read, write, execute permission
          - api_call: ["VirtualAllocE   x", "VirtualAlloc", "(Nt|Zw)AllocateVirtualMemory"]
            with:
              - argument: ["hProcess", "ProcessHandle"]
                operation: "is"
                value: "$(proc_handle)"
              - argument: ["flProtect", "Protect"]
                operation: "is"
                value: 0x40
          - api_call: ["WriteProcessMemory"]
            with:
              - argument: "hProcess"
                operation: "is"
                value: "$(proc_handle)"
          - api_call: ["SetThreadContext", "(Nt|Zw)SetContextThread"]
            with:
              - argument: "hThread"
                operation: "is"
                value: "$(thread_handle)"
        - path:
          # Map memory section with read, write, execute permission
          - api_call: "(Nt|Zw)MapViewOfSection"
            with:
              - argument: "ProcessHandle"
                operation: "is"
                value: "$(proc_handle)"
              - argument: "AccessProtection"
                operation: "is"
                value: 0x40
      # Resume thread to run injected malicious code
      - api_call: ["ResumeThread", "(Nt|Zw)ResumeThread"]
        with:
          - argument: ["hThread", "ThreadHandle"]
            operation: "is"
            value: "$(thread_handle)"
  condition: proc_hollow as sequence

Based on the signature, we can find some DSL features that make dynmx powerful:

• Definition of API call sequences with alternative paths
• Matching of API call function names with regular expressions
• Matching of argument and return values with several operators
• Storage of variables, e.g. in order to track handles in the API call sequence
• Definition of a detection condition with boolean operators (AND, OR, NOT)

If we run dynmx with the signature shown above against the function of the sample c0832b1008aa0fc828654f9762e37bda019080cbdd92bd2453a05cfb3b79abb3, we get the following output indicating that the signature was detected.

$ python3 dynmx.py detect -i 601941f00b194587c9e57c5fabaf1ef11596179bea007df9bdcdaa10f162cac9.json -s process_hollow.yml


    |
  __|         _  _    _  _  _
 /  |  |   | / |/ |  / |/ |/ |  /\/
 \_/|_/ \_/|/  |  |_/  |  |  |_/ /\_/
          /|
          \|

 Ver. 0.5 (PoC), by 0x534a


[+] Parsing 1 function log(s)
[+] Loaded 1 dynmx signature(s)
[+] Starting detection process with 1 worker(s). This probably takes some time...

[+] Result
process_hollow	c0832b1008aa0fc828654f9762e37bda019080cbdd92bd2453a05cfb3b79abb3.txt

We can get into more detail by setting the output format to detail. Now, we can see the exact API call sequence that was detected in the function log. Furthermore, we can see that the signature was detected in the process 51f0.exe.

$ python3 dynmx.py -f detail detect -i 601941f00b194587c9e57c5fabaf1ef11596179bea007df9bdcdaa10f162cac9.json -s process_hollow.yml


    |
  __|         _  _    _  _  _
 /  |  |   | / |/ |  / |/ |/ |  /\/
 \_/|_/ \_/|/  |  |_/  |  |  |_/ /\_/
          /|
          \|

 Ver. 0.5 (PoC), by 0x534a


[+] Parsing 1 function log(s)
[+] Loaded 1 dynmx signature(s)
[+] Starting detection process with 1 worker(s). This probably takes some time...

[+] Result
Function log: c0832b1008aa0fc828654f9762e37bda019080cbdd92bd2453a05cfb3b79abb3.txt
	Signature: process_hollow
		Process: 51f0.exe (PID: 3768)
		Number of Findings: 1
			Finding 0
				proc_hollow : API Call CreateProcessA (Function log line 20560, index 938)
				proc_hollow : API Call VirtualAllocEx (Function log line 20566, index 944)
				proc_hollow : API Call WriteProcessMemory (Function log line 20573, index    951)
				proc_hollow : API Call SetThreadContext (Function log line 20574, index 952)
				proc_hollow : API Call ResumeThread (Function log line 20575, index 953)

Resources

In order to extract the accessed OS resources from a function log, we can simply run the dynmx command resources against the function log. An example of the detailed output is shown below for the sample with the SHA-256 hash sum 601941f00b194587c9e57c5fabaf1ef11596179bea007df9bdcdaa10f162cac9. This is a CAPE sandbox report which is part of the Avast-CTU Public CAPEv2 Dataset.

$ python3 dynmx.py -f detail resources --input 601941f00b194587c9e57c5fabaf1ef11596179bea007df9bdcdaa10f162cac9.json


    |
  __|         _  _    _  _  _
 /  |  |   | / |/ |  / |/ |/ |  /\/
 \_/|_/ \_/|/  |  |_/  |  |  |_/ /\_/
          /|
          \|

 Ver. 0.5 (PoC), by 0x534a


[+] Parsing 1 function log(s)
[+] Processing function log(s) with the command 'resources'...

[+] Result
Function log: 601941f00b194587c9e57c5fabaf1ef11596179bea007df9bdcdaa10f162cac9.json (/Users/sijansen/Documents/dev/dynmx_flogs/cape/Public_Avast_CTU_CAPEv2_Dataset_Full/extracted/601941f00b194587c9e57c5fabaf1ef11596179bea007df9bdcdaa10f162cac9.json)
	Process: 601941F00B194587C9E5.exe (PID: 2008)
		Filesystem:
			C:\Windows\SysWOW64\en-US\SETUPAPI.dll.mui (CREATE)
			API-MS-Win-Core-LocalRegistry-L1-1-0.dll (EXECUTE)
			C:\Windows\SysWOW64\ntdll.dll (READ)
			USER32.dll (EXECUTE)
			KERNEL32.   dll (EXECUTE)
			C:\Windows\Globalization\Sorting\sortdefault.nls (CREATE)
		Registry:
			HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\OLEAUT (READ)
			HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Setup (READ)
			HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Setup\SourcePath (READ)
			HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion (READ)
			HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\DevicePath (READ)
			HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Internet Settings (READ)
			HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Internet Settings\DisableImprovedZoneCheck (READ)
			HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows\CurrentVersion\Internet Settings (READ)
			HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows\CurrentVersion\Internet Settings\Security_HKLM_only (READ)
	Process: 601941F00B194587C9E5.exe (PID: 1800)
		Filesystem:
		   	C:\Windows\SysWOW64\en-US\SETUPAPI.dll.mui (CREATE)
			API-MS-Win-Core-LocalRegistry-L1-1-0.dll (EXECUTE)
			C:\Windows\SysWOW64\ntdll.dll (READ)
			USER32.dll (EXECUTE)
			KERNEL32.dll (EXECUTE)
			[...]
			C:\Users\comp\AppData\Local\vscmouse (READ)
			C:\Users\comp\AppData\Local\vscmouse\vscmouse.exe:Zone.Identifier (DELETE)
		Registry:
			HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\OLEAUT (READ)
			HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Setup (READ)
			[...]
	Process: vscmouse.exe (PID: 900)
		Filesystem:
			C:\Windows\SysWOW64\en-US\SETUPAPI.dll.mui (CREATE)
			API-MS-Win-Core-LocalRegistry-L1-1-0.dll (EXECUTE)
			C:\Windows\SysWOW64\ntdll.dll (READ)
			USER32.dll (EXECUTE)
			KERNEL32.dll (EXECUTE)
			C:\Windows\Globalization\Sorting\sortdefault.nls (CREATE)
		Registry:
			HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\OLEAUT (READ)
			HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\C   urrentVersion\Setup (READ)
			HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Setup\SourcePath (READ)
			HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion (READ)
			HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\DevicePath (READ)
			HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Internet Settings (READ)
			HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Internet Settings\DisableImprovedZoneCheck (READ)
			HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows\CurrentVersion\Internet Settings (READ)
			HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows\CurrentVersion\Internet Settings\Security_HKLM_only (READ)
	Process: vscmouse.exe (PID: 3036)
		Filesystem:
			C:\Windows\SysWOW64\en-US\SETUPAPI.dll.mui (CREATE)
			API-MS-Win-Core-LocalRegistry-L1-1-0.dll (EXECUTE)
			C:\Windows\SysWOW64\ntdll.dll (READ)
			USER32.dll (EXECUTE)
			KERNEL32.dll (EXECUTE)
			   C:\Windows\Globalization\Sorting\sortdefault.nls (CREATE)
			C:\ (READ)
			C:\Windows\System32\uxtheme.dll (EXECUTE)
			dwmapi.dll (EXECUTE)
			advapi32.dll (EXECUTE)
			shell32.dll (EXECUTE)
			C:\Users\comp\AppData\Local\vscmouse\vscmouse.exe (CREATE,READ)
			C:\Users\comp\AppData\Local\iproppass\iproppass.exe (DELETE)
			crypt32.dll (EXECUTE)
			urlmon.dll (EXECUTE)
			userenv.dll (EXECUTE)
			wininet.dll (EXECUTE)
			wtsapi32.dll (EXECUTE)
			CRYPTSP.dll (EXECUTE)
			CRYPTBASE.dll (EXECUTE)
			ole32.dll (EXECUTE)
			OLEAUT32.dll (EXECUTE)
			C:\Windows\SysWOW64\oleaut32.dll (EXECUTE)
			IPHLPAPI.DLL (EXECUTE)
			DHCPCSVC.DLL (EXECUTE)
			C:\Users\comp\AppData\Roaming\Microsoft\Network\Connections\Pbk\_hiddenPbk\ (CREATE)
			C:\Users\comp\AppData\Roaming\Microsoft\Network\Connections\Pbk\_hiddenPbk\rasphone.pbk (CREATE,READ)
		Registry:
			HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\OLEAUT (READ   )
			HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Setup (READ)
			[...]
		Network:
			24.151.31.150:465 (READ)
			http://24.151.31.150:465 (READ,WRITE)
			107.10.49.252:80 (READ)
			http://107.10.49.252:80 (READ,WRITE)

Based on the shown output and the accessed resources, we can deduce some malware features:

• Within the process 601941F00B194587C9E5.exe (PID 1800), the Zone Identifier of the file C:\Users\comp\AppData\Local\vscmouse\vscmouse.exe is deleted
• Some DLLs are loaded dynamically
• The process vscmouse.exe (PID: 3036) connects to the network endpoints http://24.151.31.150:465 and http://107.10.49.252:80

The accessed resources are interesting for identifying host- and network-based detection indicators. In addition, resources can be used in dynmx signatures. A popular example is the detection of persistence mechanisms in the Registry.

pip3 install -r requirements.txt

$ python3 dynmx.py -h
usage: dynmx.py [-h] [--format {overview,detail}] [--show-log] [--log LOG] [--log-level {debug,info,error}] [--worker N] {detect,check,convert,stats,resources} ...

Detect dynmx signatures in dynamic program execution information (function logs)

optional arguments:
  -h, --help            show this help message and exit
  --format {overview,detail}, -f {overview,detail}
                        Output format
  --show-log            Show all log output on stdout
  --log LOG, -l LOG     log file
  --log-level {debug,info,error}
                        Log level (default: info)
  --worker N, -w N      Number of workers to spawn (default: number of processors - 2)

sub-commands:
  task to perform

  {detect,check,convert,stats,resources}
    detect              Detects a dynmx signature
    check               Checks the syntax of dynmx signature(s)
    convert                Converts function logs to the dynmx generic function log format
    stats               Statistics of function logs
    resources           Resource activity derived from function log

$ python3 dynmx.py detect -h
usage: dynmx.py detect [-h] --sig SIG [SIG ...] --input INPUT [INPUT ...] [--recursive] [--json-result JSON_RESULT] [--runtime-result RUNTIME_RESULT] [--detect-all]

optional arguments:
  -h, --help            show this help message and exit
  --recursive, -r       Search for input files recursively
  --json-result JSON_RESULT
                        JSON formatted result file
  --runtime-result RUNTIME_RESULT
                        Runtime statistics file formatted in CSV
  --detect-all          Detect signature in all processes and do not stop after the first detection

required arguments:
  --sig SIG [SIG ...], -s SIG [SIG ...]
                        dynmx signature(s) to detect
  --input INPUT [INPUT ...], -i INPUT [INPUT ...]
                        Input files

    |
  __|         _  _    _  _  _
 /  |  |   | / |/ |  / |/ |/ |  /\/
 \_/|_/ \_/|/  |  |_/  |  |  |_/ /\_/
          /|
          \|

 Ver. 0.5 (PoC), by 0x534a


[+] Log output
2023-06-27 19:07:38,068+0000 [INFO] (__main__) [PID: 13315] []: Start of dynmx run
[...]
[+] End of log output

[+] Result
[...]

python3 dynmx.py -w 1 detect -i "flog.txt" -s dynmx_signature.yml

python3 dynmx.py convert -i "flog.txt" -o /tmp/

python3 dynmx.py check -s dynmx_signature.yml

python3 dynmx.py -f detail resources -i "flog.txt"

HardHatC2 - A C# Command And Control Framework

A cross-platform, collaborative, Command & Control framework written in C#, designed for red teaming and ease of use.

HardHat is a multiplayer C# .NET-based command and control framework. Designed to aid in red team engagements and penetration testing. HardHat aims to improve the quality of life factors during engagements by providing an easy-to-use but still robust C2 framework.
It contains three primary components, an ASP.NET teamserver, a blazor .NET client, and C# based implants.

Release Tracking

Alpha Release - 3/29/23 NOTE: HardHat is in Alpha release; it will have bugs, missing features, and unexpected things will happen. Thank you for trying it, and please report back any issues or missing features so they can be addressed.

Community

Discord Join the community to talk about HardHat C2, Programming, Red teaming and general cyber security things The discord community is also a great way to request help, submit new features, stay up to date on the latest additions, and submit bugs.

Features

Teamserver & Client

• Per-operator accounts with account tiers to allow customized access control and features, including view-only guest modes, team-lead opsec approval(WIP), and admin accounts for general operation management.
• Managers (Listeners)
• Dynamic Payload Generation (Exe, Dll, shellcode, PowerShell command)
• Creation & editing of C2 profiles on the fly in the client
• Customization of payload generation
  • sleep time/jitter
  • kill date
  • working hours
  • type (Exe, Dll, Shellcode, ps command)
  • Included commands(WIP)
  • option to run confuser
• File upload & Downloads
• Graph View
• File Browser GUI
• Event Log
• JSON logging for events & tasks
• Loot tracking (Creds, downloads)
• IOC tracing
• Pivot proxies (SOCKS 4a, Port forwards)
• Cred store
• Autocomplete command history
• Detailed help command
• Interactive bash terminal command if the client is on linux or powershell on windows, this allows automatic parsing and logging of terminal commands like proxychains
• Persistent database storage of teamserver items (User accounts, Managers, Engineers, Events, tasks, creds, downloads, uploads, etc. )
• Recon Entity Tracking (track info about users/devices, random metadata as needed)
• Shared files for some commands (see teamserver page for details)
• tab-based interact window for command issuing
• table-based output option for some commands like ls, ps, etc.
• Auto parsing of output from seatbelt to create "recon entities" and fill entries to reference back to later easily
• Dark and Light
  冷
  theme

Engineers

• C# .NET framework implant for windows devices, currently only CLR/.NET 4 support
• atm only one implant, but looking to add others
• It can be generated as EXE, DLL, shellcode, or PowerShell stager
• Rc4 encryption of payload memory & heap when sleeping (Exe / DLL only)
• AES encryption of all network communication
• ConfuserEx integration for obfuscation
• HTTP, HTTPS, TCP, SMB communication
  • TCP & SMB can work P2P in a bind or reverse setups
• Unique per implant key generated at compile time
• multiple callback URI's depending on the C2 profile
• P/Invoke & D/Invoke integration for windows API calls
• SOCKS 4a support
• Reverse Port Forward & Port Forwards
• All commands run as async cancellable jobs
  • Option to run commands sync if desired
• Inline assembly execution & inline shellcode execution
• DLL Injection
• Execute assembly & Mimikatz integration
• Mimikatz is not built into the implant but is pushed when specific commands are issued
• Various localhost & network enumeration tools
• Token manipulation commands
  • Steal Token Mask(WIP)
• Lateral Movement Commands
• Jump (psexec, wmi, wmi-ps, winrm, dcom)
• Remote Execution (WIP)
• AMSI & ETW Patching
• Unmanaged Powershell
• Script Store (can load multiple scripts at once if needed)
• Spawn & Inject
  • Spawn-to is configurable
• run, shell & execute

Documentation

documentation can be found at docs

Getting Started

Prerequisites

• Installation of the .net 7 SDK from Microsoft
• Once installed, the teamserver and client are started with dotnet run

Teamserver

To configure the team server's starting address (where clients will connect), edit the HardHatC2\TeamServer\Properties\LaunchSettings.json changing the "applicationUrl": "https://127.0.0.1:5000" to the desired location and port. start the teamserver with dotnet run from its top-level folder ../HrdHatC2/Teamserver/

HardHat Client

1. When starting the client to set the target teamserver location, include it in the command line dotnet run https://127.0.0.1:5000 for example
2. open a web browser and navigate to https://localhost:7096/ if this works, you should see the login page
3. Log in with the HardHat_Admin user (Password is printed on first TeamServer startup)
4. Navigate to the settings page & create a new user if successful, a message should appear, then you may log in with that account to access the full client

Contributions & Bug Reports

Code contributions are welcome feel free to submit feature requests, pull requests or send me your ideas on discord.

DotDumper - An Automatic Unpacker And Logger For DotNet Framework Targeting Files

An automatic unpacker and logger for DotNet Framework targeting files! This tool has been unveiled at Black Hat USA 2022.

The automatic detection and classification of any given file in a reliable manner is often considered the holy grail of malware analysis. The trials and tribulations to get there are plenty, which is why the creation of such a system is held in high regard. When it comes to DotNet targeting binaries, our new open-source tool DotDumper aims to assist in several of the crucial steps along the way: logging (in-memory) activity, dumping interesting memory segments, and extracting characteristics from the given sample.

Why DotDumper?

In brief, manual unpacking is a tedious process which consumes a disproportional amount of time for analysts. Obfuscated binaries further increase the time an analyst must spend to unpack a given file. When scaling this, organizations need numerous analysts who dissect malware daily, likely in combination with a scalable sandbox. The lost valuable time could be used to dig into interesting campaigns or samples to uncover new threats, rather than the mundane generic malware that is widely spread. Afterall, analysts look for the few needles in the haystack.

So, what difference does DotDumper make? Running a DotNet based malware sample via DotDumper provides log files of crucial, contextualizing, and common function calls in three formats (human readable plaintext, JSON, and XML), as well as copies from useful in-memory segments. As such, an analyst can skim through the function call log. Additionally, the dumped files can be scanned to classify them, providing additional insight into the malware sample and the data it contains. This cuts down on time vital to the triage and incident response processes, and frees up SOC analyst and researcher time for more sophisticated analysis needs.

Features

To log and dump the contextualizing function calls and their results, DotDumper uses a mixture of reflection and managed hooks, all written in pure C#. Below, key features will be highlighted and elaborated upon, in combination with excerpts of DotDumper’s results of a packed AgentTesla stealer sample, the hashes of which are below.

Using the command-line interface

DotDumper is accessible through a command-line interface, with a variety of arguments. The image below shows the help menu. Note that not all arguments will be discussed, but rather the most used ones.

The minimal requirement to run a given sample, is to provide the “-file” argument, along with a file name or file path. If a full path is given, it is used. If a file name is given, the current working directory is checked, as well as the folder of DotDumper’s executable location.

Unless a directory name is provided, the “-log” folder name is set equal to the file name of the sample without the extension (if any). The folder is located in the same folder as DotDumper resides in, which is where the logs and dumped files will be saved in.

In the case of a library, or an alternative entry point into a binary, one must override the entry point using “-overrideEntry true”. Additionally, one has to provide the fully qualified class, which includes the name space using “-fqcn My.NameSpace.MyClass”. This tells DotDumper which class to select, which is where the provided function name (using “-functionName MyFunction”) is retrieved.

If the selected function requires arguments, one has to provide the number of arguments using “-argc” and the number of required arguments. The argument types and values are to be provided as “string|myValue int|9”. Note that when spaces are used in the values, the argument on the command-line interface needs to be encapsulated between quotes to ensure it is passed as a single argument.

Other less frequently used options such as “-raceTime” or “-deprecated” are safe in their default settings but might require tweaking in the future due to changes in the DotNet Framework. They are currently exposed in the command-line interface to easily allow changes, if need be, even if one is using an older version of DotDumper when the time comes.

Logging and dumping

Logging and dumping are the two core features of DotDumper. To minimize the amount of time the analysis takes, the logging should provide context to the analyst. This is done by providing the analyst with the following information for each logged function call:

• A stack trace based on the function’s caller
• Information regarding the assembly object where the call originated from, such as the name, version, and cryptographic hashes
• The parent assembly, from which the call originates if it is not the original sample
• The type, name, and value of the function’s arguments
• The type, name, and value of function’s return value, if any
• A list of files which are dumped to disk which correspond with the given function call

Note that for each dumped file, the file name is equal to the file’s SHA-256 hash.

To clarify the above, an excerpt of a log is given below. The excerpt shows the details for the aforementioned AgentTesla sample, where it loads the second stage using DotNet’s Assembly.Load function.

First, the local system time is given, together with the original function’s return type, name, and argument(s). Second, the stack trace is given, where it shows that the sample’s main function leads to a constructor, initialises the components, and calls two custom functions. The Assembly.Load function was called from within “NavigationLib.TaskEightBestOil.GGGGGGGGGGGGGGGGGGGG(String str)”. This provides context for the analyst to find the code around this call if it is of interest.

Then, information regarding the assembly call order is given. The more stages are loaded, the more complex it becomes to see via which stages the call came to be. One normally expects one stage to load the next, but in some cases later stages utilize previous stages in a non-linear order. Additionally, information regarding the originating assembly is given to further enrich the data for the analyst.

Next, the parent hash is given. The parent of a stage is the previous stage, which in this example is not yet present. The newly loaded stage will have this stage as its parent. This allows the analyst to correlate events more easily.

Finally, the function’s return type and value are stored, along with the type, name, and value of each argument that is passed to the hooked function. If any variable is larger than 100 bytes in size, it is stored on the disk instead. A reference is then inserted in the log to reference the file, rather than showing the value. The threshold has been set to avoid hiccups in the printing of the log, as some arrays are thousands of indices in size.

Reflection

Per Microsoft’s documentation, reflection is best summarized as “[…] provides objects that encapsulate assemblies, modules, and types”. In short, this allows the dynamic creation and invocation of DotNet classes and functions from the malware sample. DotDumper contains a reflective loader which allows an analyst to load and analyze both executables and libraries, as long as they are DotNet Framework based.

To utilize the loader, one has to opt to overwrite the entry point in the command-line interface, specify the class (including the namespace it resides in) and function name within a given file. Optionally, one can provide arguments to the specified function, for all native types and arrays thereof. Examples of native types are int, string, char, and arrays such as int[], string[], and char[]. All the arguments are to be provided via the command-line interface, where both the type and the value are to be specified.

Not overriding the entry point results in the default entry point being used. By default, an empty string array is passed towards the sample’s main function, as if the sample is executed without arguments. Additionally, reflection is often used by loaders to invoke a given function in a given class in the next stage. Sometimes, arguments are passed along as well, which are used later to decrypt a resource. In the aforementioned AgentTesla sample, this exact scenario plays out. DotDumper’s invoke related hooks log these occurrences, as can be seen below.

The function name in the first line is not an internal function of the DotNet Framework, but rather a call to a specific function in the second stage. The types and names of the three arguments are listed in the function signature. Their values can be found in the function argument information section. This would allow an analyst to load the second stage in a custom loader with the given values for the arguments, or even do this using DotDumper by loading the previously dumped stage and providing the arguments.

Managed hooks

Before going into managed hooks, one needs to understand how hooks work. There are two main variables to consider here: the target function and a controlled function which is referred to as the hook. Simply put, the memory at the target function (i.e. Assembly.Load) is altered to instead to jump to the hook. As such, the program’s execution flow is diverted. The hook can then perform arbitrary actions, optionally call the original function, after which it returns the execution to the caller together with a return value if need be. The diagram below illustrates this process.

Knowing what hooks are is essential to understand what managed hooks are. Managed code is executed in a virtual and managed environment, such as the DotNet runtime or Java’s virtual machine. Obtaining the memory address where the managed function resides differs from an unmanaged language such as C. Once the correct memory addresses for both functions have been obtained, the hook can be set by directly accessing memory using unsafe C#, along with DotNet’s interoperability service to call native Windows API functionality.

Easily extendible

Since DotDumper is written in pure C# without any external dependencies, one can easily extend the framework using Visual Studio. The code is documented in this blog, on GitHub, and in classes, in functions, and in-line in the source code. This, in combination with the clear naming scheme, allows anyone to modify the tool as they see fit, minimizing the time and effort that one needs to spend to understand the tool. Instead, it allows developers and analysts alike to focus their efforts on the tool’s improvement.

Differences with known tooling

With the goal and features of DotDumper clear, it might seem as if there’s overlap with known publicly available tools such as ILSpy, dnSpyEx, de4dot, or pe-sieve. Note that there is no intention to proclaim one tool is better than another, but rather how the tools differ.

DotDumper’s goal is to log and dump crucial, contextualizing, and common function calls from DotNet targeting samples. ILSpy is a DotNet disassembler and decompiler, but does not allow the execution of the file. dnSpyEx (and its predecessor dnSpy) utilise ILSpy as the disassembler and decompiler component, while adding a debugger. This allows one to manually inspect and manipulate memory. de4dot is solely used to deobfuscate DotNet binaries, improving the code’s readability for human eyes. The last tool in this comparison, pe-sieve, is meant to detect and dump malware from running processes, disregarding the used programming language. The table below provides a graphical overview of the above-mentioned tools.

Future work

DotDumper is under constant review and development, all of which is focused on two main areas of interest: bug fixing and the addition of new features. During the development, the code was tested, but due to injection of hooks into the DotNet Framework’s functions which can be subject to change, it’s very well possible that there are bugs in the code. Anyone who encounters a bug is urged to open an issue on the GitHub repository, which will then be looked at. The suggestion of new features is also possible via the GitHub repository. For those with a GitHub account, or for those who rather not publicly interact, feel free to send me a private message on my Twitter.

Needless to say, if you've used DotDumper during an analysis, or used it in a creative way, feel free to reach out in public or in private! There’s nothing like hearing about the usage of a home-made tool!

There is more in store for DotDumper, and an update will be sent out to the community once it is available!

FUD-UUID-Shellcode - Another shellcode injection technique using C++ that attempts to bypass Windows Defender using XOR encryption sorcery and UUID strings madness

Introduction

Another shellcode injection technique using C++ that attempts to bypass Windows Defender using XOR encryption sorcery and UUID strings madness :).

How it works

Shellcode generation

• Firstly, generate a payload in binary format( using either CobaltStrike or msfvenom ) for instance, in msfvenom, you can do it like so( the payload I'm using is for illustration purposes, you can use whatever payload you want ):

  msfvenom -p windows/messagebox  -f raw -o shellcode.bin

• Then convert the shellcode( in binary/raw format ) into a UUID string format using the Python3 script, bin_to_uuid.py:

  ./bin_to_uuid.py -p shellcode.bin > uuid.txt

• xor encrypt the UUID strings in the uuid.txt using the Python3 script, xor_encryptor.py.

  ./xor_encryptor.py uuid.txt > xor_crypted_out.txt

• Copy the C-style array in the file, xor_crypted_out.txt, and paste it in the C++ file as an array of unsigned char i.e. unsigned char payload[]{your_output_from_xor_crypted_out.txt}

Execution

This shellcode injection technique comprises the following subsequent steps:

• First things first, it allocates virtual memory for payload execution and residence via VirtualAlloc
• It xor decrypts the payload using the xor key value
• Uses UuidFromStringA to convert UUID strings into their binary representation and store them in the previously allocated memory. This is used to avoid the usage of suspicious APIs like WriteProcessMemory or memcpy.
• Use EnumChildWindows to execute the payload previously loaded into memory( in step 1 )

What makes it unique?

• It doesn't use standard functions like memcpy or WriteProcessMemory which are known to raise alarms to AVs/EDRs, this program uses the Windows API function called UuidFromStringA which can be used to decode data as well as write it to memory( Isn't that great folks? And please don't say "NO!" :) ).
• It uses the function call obfuscation trick to call the Windows API functions
• Lastly, because it looks unique :) ( Isn't it? :) )

Important

• You have to change the xor key(row 86) to what you wish. This can be done in the ./xor_encryptor.py python3 script by changing the KEY variable.
• You have to change the default executable filename value(row 90) to your filename.
• The command for compiling is provided in the C++ file( around the top ). NB: mingw was used but you can use whichever compiler you prefer. :)

Compile

make

Proof-of-Concept( PoC )

Static Analysis

AV Scan results

The binary was scanned using antiscan.me on 01/08/2022.

Credits

https://research.nccgroup.com/2021/01/23/rift-analysing-a-lazarus-shellcode-execution-method/

OffensiveVBA - Code Execution And AV Evasion Methods For Macros In Office Documents

In preparation for a VBS AV Evasion Stream/Video I was doing some research for Office Macro code execution methods and evasion techniques.

The list got longer and longer and I found no central place for offensive VBA templates - so this repo can be used for such. It is very far away from being complete. If you know any other cool technique or useful template feel free to contribute and create a pull request!

Most of the templates in this repo were already published somewhere. I just copy pasted most templates from ms-docs sites, blog posts or from other tools.

Templates in this repo

Missing - ToDos

Obfuscators / Payload generators

1. VBad
2. wePWNise
3. VisualBasicObfuscator - needs some modification as it doesn't split up lines and is therefore not usable for office document macros
4. macro_pack
5. shellcode2vbscript.py
6. EvilClippy
7. OfficePurge
8. SharpShooter
9. VBS-Obfuscator-in-Python - - needs some modification as it doesn't split up lines and is therefore not usable for office document macros

Credits / usefull resources

ASR bypass: http://blog.sevagas.com/IMG/pdf/bypass_windows_defender_attack_surface_reduction.pdf

Shellcode to VBScript conversion: https://github.com/DidierStevens/DidierStevensSuite/blob/master/shellcode2vbscript.py

Bypass AMSI in VBA: https://outflank.nl/blog/2019/04/17/bypassing-amsi-for-vba/

VBA purging: https://www.mandiant.com/resources/purgalicious-vba-macro-obfuscation-with-vba-purging

F-Secure VBA Evasion and detection post: https://blog.f-secure.com/dechaining-macros-and-evading-edr/

One more F-Secure blog: https://labs.f-secure.com/archive/dll-tricks-with-vba-to-improve-offensive-macro-capability/