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Detectionmediumtest

Potential AMSI Bypass Script Using NULL Bits

Detects usage of special strings/null bits in order to potentially bypass AMSI functionalities

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Nasreddine Bencherchali (Nextron Systems)Created Wed Jan 04Updated Tue May 09fa2559c8-1197-471d-9cdd-05a0273d4522windows
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:
            - "if(0){{{0}}}' -f $(0 -as [char]) +"
            - "#<NULL>"
    condition: selection
False Positives
Unknown

False positive likelihood has not been assessed. Additional context may be needed during triage.

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

Potential AMSI Bypass Using NULL Bits

Detects usage of special strings/null bits in order to potentially bypass AMSI functionalities

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

Rule Metadata
Rule ID
fa2559c8-1197-471d-9cdd-05a0273d4522
Status
test
Level
medium
Type
Detection
Created
Wed Jan 04
Modified
Tue May 09
Author
Nasreddine Bencherchali (Nextron Systems)
Path
rules/windows/powershell/powershell_script/posh_ps_amsi_null_bits_bypass.yml
Raw Tags
attack.defense-evasionattack.t1562.001
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