Detection rules › Splunk
PowerShell CreateDecryptor (PowerShell)
Threat actors may abuse the CreateDecryptor() method within PowerShell scripts to dynamically decrypt embedded payloads, configuration files, or sensitive data at runtime. CreateDecryptor() is part of legitimate .NET cryptographic operations, but its presence in PowerShell ScriptBlock or CommandLine activity — especially outside normal application behavior — often signals malware unpacking, fileless attacks, or ransomware staging. This use case detects references to CreateDecryptor in PowerShell activity, potentially indicating obfuscated payload execution or preparation for in-memory attacks.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Execution | T1059.001 Command and Scripting Interpreter: PowerShell |
| Stealth | T1027 Obfuscated Files or Information |
References
Event coverage
| Provider | Event | Title |
|---|---|---|
| PowerShell | Event ID 4103 | Payload Context: ContextInfo User Data: UserData. |
| PowerShell | Event ID 4104 | Creating Scriptblock text (MessageNumber of MessageTotal). |
Rule body yaml
id: '45003.90177'
title: PowerShell CreateDecryptor
description: Threat actors may abuse the CreateDecryptor() method within PowerShell
scripts to dynamically decrypt embedded payloads, configuration files, or sensitive
data at runtime. CreateDecryptor() is part of legitimate .NET cryptographic operations,
but its presence in PowerShell ScriptBlock or CommandLine activity — especially
outside normal application behavior — often signals malware unpacking, fileless
attacks, or ransomware staging. This use case detects references to CreateDecryptor
in PowerShell activity, potentially indicating obfuscated payload execution or preparation
for in-memory attacks.
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_powershell` (TERM(EventCode=4103) OR
"EventID>4103<" OR TERM(EventCode=4104) OR "EventID>4104<") "CreateDecryptor" |
regex process="(?i)CreateDecryptor" | table _time, host, user process, process_*,
signature_id | bin span=1s | stats values(*) as * by _time, host '
techniques:
- execution:command and scripting interpreter:powershell
- defense-evasion:obfuscated files or information
technique_id:
- T1059.001
- T1027
data_category:
- PowerShell logs
- Process command-line parameters
references:
- https://www.cybereason.com/blog/threat-analysis-lummastealer-2.0
- https://learn.microsoft.com/en-us/dotnet/api/system.security.cryptography.symmetricalgorithm.createdecryptor?view=net-9.0
- https://www.virustotal.com/gui/file/034694376c291c82789e7dc2c8771a4dff47c1c447f2ea7427edb968f480fa71
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_powershell` (TERM(EventCode=4103) OR "EventID>4103<" OR TERM(EventCode=4104) OR "EventID>4104<") "CreateDecryptor"
Stage 2: regex
| regex process="(?i)CreateDecryptor"
Stage 3: table
| table _time, host, user process, process_*, signature_id
Stage 4: bucket
| bin span=1s
Stage 5: stats
| stats values(*) as * by _time, host
Indicators
Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.
Search terms
Bare-string tokens in the SPL search body. Splunk matches each token against _raw (the untyped raw event text) anywhere it appears, not against a specific field. These don't surface in the Indicators table because they aren't predicates on a known field.
| Stage | Term |
|---|---|
| 1 | TERM |
| 1 | "EventID>4103<" |
| 1 | TERM |
| 1 | "EventID>4104<" |
| 1 | "CreateDecryptor" |