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Detectionmediumtest

Suspicious FromBase64String Usage On Gzip Archive - Ps Script

Detects attempts of decoding a base64 Gzip archive in a PowerShell script. This technique is often used as a method to load malicious content into memory afterward.

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Launch
François HubautCreated Fri Dec 23df69cb1d-b891-4cd9-90c7-d617d90100cewindows
Log Source
WindowsPowerShell Script
ProductWindows← raw: windows
CategoryPowerShell Script← raw: ps_script

Definition

Requirements: Script Block Logging must be enabled

Detection Logic
Detection Logic1 selector
detection:
    selection:
        ScriptBlockText|contains|all:
            - 'FromBase64String'
            - 'MemoryStream'
            - 'H4sI'
    condition: selection
False Positives

Legitimate administrative script

References
1
Resolving title…
speakerdeck.com
MITRE ATT&CK
Related Rules
SimilarDetectionmedium

Suspicious FromBase64String Usage On Gzip Archive - Process Creation

Detects attempts of decoding a base64 Gzip archive via PowerShell. This technique is often used as a method to load malicious content into memory afterward.

Detects similar activity. Both rules may fire on overlapping events.

Rule Metadata
Rule ID
df69cb1d-b891-4cd9-90c7-d617d90100ce
Status
test
Level
medium
Type
Detection
Created
Fri Dec 23
Author
François Hubaut
Path
rules/windows/powershell/powershell_script/posh_ps_frombase64string_archive.yml
Raw Tags
attack.command-and-controlattack.t1132.001
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