Detection rules › Splunk
Powershell Using memory As Backing Store
The following analytic detects suspicious PowerShell script execution using memory streams as a backing store, identified via EventCode 4104. It leverages PowerShell Script Block Logging to capture scripts that create new objects with memory streams, often used to decompress and execute payloads in memory. This activity is significant as it indicates potential in-memory execution of malicious code, bypassing traditional file-based detection. If confirmed malicious, this technique could allow attackers to execute arbitrary code, maintain persistence, or escalate privileges without leaving a trace on the disk.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Execution | T1059.001 Command and Scripting Interpreter: PowerShell |
Event coverage
| Provider | Event ID | Title |
|---|---|---|
| PowerShell | 4104 | Creating Scriptblock text (MessageNumber of MessageTotal). |
Stages and Predicates
Stage 1: search
search EventCode=4104 ScriptBlockText="*IO.MemoryStream*" ScriptBlockText="*New-Object*"
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 3 filters this rule applies)
- Potential PowerShell Obfuscation via Backtick-Escaped Variable Expansion (drops 3 filters this rule applies)
- Potential PowerShell Obfuscation via Character Array Reconstruction (drops 3 filters this rule applies)
- Potential PowerShell Obfuscation via Concatenated Dynamic Command Invocation (drops 3 filters this rule applies)
- Potential PowerShell Obfuscation via High Numeric Character Proportion (drops 3 filters this rule applies)
- Potential Dynamic IEX Reconstruction via Environment Variables (drops 3 filters this rule applies)
- Dynamic IEX Reconstruction via Method String Access (drops 3 filters this rule applies)
- PowerShell Obfuscation via Negative Index String Reversal (drops 3 filters this rule applies)
- Potential PowerShell Obfuscation via Reverse Keywords (drops 3 filters this rule applies)
- Potential PowerShell Obfuscation via String Concatenation (drops 3 filters this rule applies)
- Potential PowerShell Obfuscation via String Reordering (drops 3 filters this rule applies)
- Potential PowerShell Obfuscation via Special Character Overuse (drops 3 filters this rule applies)
- PowerShell 4104 Hunting (drops 2 filters this rule applies)