Detection rules › Splunk
User Discovery With Env Vars PowerShell Script Block
The following analytic detects the use of PowerShell environment variables to identify the current logged user by leveraging PowerShell Script Block Logging (EventCode=4104). This method monitors script blocks containing $env:UserName or [System.Environment]::UserName. Identifying this activity is significant as adversaries and Red Teams may use it for situational awareness and Active Directory discovery on compromised endpoints. If confirmed malicious, this activity could allow attackers to gain insights into user context, aiding in further exploitation and lateral movement within the network.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Discovery | T1033 System Owner/User Discovery |
Event coverage
| Provider | Event ID | Title |
|---|---|---|
| PowerShell | 4104 | Creating Scriptblock text (MessageNumber of MessageTotal). |
Stages and Predicates
Stage 1: search
search (ScriptBlockText="*$env:UserName*" OR ScriptBlockText="*[System.Environment]::UserName*") EventCode=4104
Stage 2: fillnull
fillnull
Stage 3: stats
stats BY dest, signature, signature_id, user_id, vendor_product, EventID, Guid, Opcode, Name, Path, ProcessID, ScriptBlockId, ScriptBlockText
Stage 4: search
search
Stage 5: search
search
Stage 6: search
search `macro`
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.
| Field | Kind | Values |
|---|---|---|
EventCode | eq |
|
ScriptBlockText | eq |
|
Neighbors
Broader alternatives (more inclusive than this rule)
These rules match a superset of what this rule catches. They cover the same events plus more. Use them if you want wider coverage and can absorb more false positives.
- Potential PowerShell Obfuscation via Invalid Escape Sequences (drops 2 filters this rule applies)
- Potential PowerShell Obfuscation via Backtick-Escaped Variable Expansion (drops 2 filters this rule applies)
- Potential PowerShell Obfuscation via Character Array Reconstruction (drops 2 filters this rule applies)
- Potential PowerShell Obfuscation via Concatenated Dynamic Command Invocation (drops 2 filters this rule applies)
- Potential PowerShell Obfuscation via High Numeric Character Proportion (drops 2 filters this rule applies)
- Potential Dynamic IEX Reconstruction via Environment Variables (drops 2 filters this rule applies)
- Dynamic IEX Reconstruction via Method String Access (drops 2 filters this rule applies)
- PowerShell Obfuscation via Negative Index String Reversal (drops 2 filters this rule applies)
- Potential PowerShell Obfuscation via Reverse Keywords (drops 2 filters this rule applies)
- Potential PowerShell Obfuscation via String Concatenation (drops 2 filters this rule applies)
- Potential PowerShell Obfuscation via String Reordering (drops 2 filters this rule applies)
- Potential PowerShell Obfuscation via Special Character Overuse (drops 2 filters this rule applies)
- PowerShell 4104 Hunting (drops 1 filter this rule applies)