Sigma rule: Invocation Of Crypto-Classes From The "Cryptography" PowerShell Namespace

Rule

Title

Invocation Of Crypto-Classes From The "Cryptography" PowerShell Namespace

Status

test

Level

medium

Author

Andreas Braathen (mnemonic.io)

Date

2023-12-01

File

rules-threat-hunting/windows/process_creation/proc_creation_win_powershell_crypto_namespace.yml

Commit

ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects the invocation of PowerShell commands with references to classes from the "System.Security.Cryptography" namespace.
The PowerShell namespace "System.Security.Cryptography" provides classes for on-the-fly encryption and decryption.
These can be used for example in decrypting malicious payload for defense evasion.

Log source

product

windows

category

process_creation

Detection

selection_img:
    - Image|endswith:
          - '\powershell.exe'
          - '\pwsh.exe'
    - OriginalFileName:
          - 'PowerShell.EXE'
          - 'pwsh.dll'
selection_cmdlet_namespace:
    CommandLine|contains: 'System.Security.Cryptography.'
selection_cmdlet_classes:
    CommandLine|contains:
        - '.AesCryptoServiceProvider'
        - '.DESCryptoServiceProvider'
        - '.DSACryptoServiceProvider'
        - '.RC2CryptoServiceProvider'
        - '.Rijndael'
        - '.RSACryptoServiceProvider'
        - '.TripleDESCryptoServiceProvider'
condition: all of selection_*

False positives (as the rule lists them)

• Classes are legitimately used, but less so when e.g. parents with low prevalence or decryption of content in temporary folders.

Tags

• attack.execution
• attack.stealth
• attack.t1059.001
• attack.t1027.010
• detection.threat-hunting

MITRE ATT&CK ids this rule names

• T1027.010
• T1059.001

References

• https://learn.microsoft.com/en-us/dotnet/api/system.security.cryptography?view=net-8.0
• https://blogs.vmware.com/security/2023/11/jupyter-rising-an-update-on-jupyter-infostealer.html
• https://www.virustotal.com/gui/file/39102fb7bb6a74a9c8cb6d46419f9015b381199ea8524c1376672b30fffd69d2

Read on 2026-11-03T00:58:21.399Z under licence sigma-drl-1.1@d5f4c36a from https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules-threat-hunting/windows/process_creation/proc_creation_win_powershell_crypto_namespace.yml