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Detectionmediumtest

Potential AMSI Bypass Using NULL Bits

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

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Launch
Nasreddine Bencherchali (Nextron Systems)Created Wed Jan 04Updated Tue May 0992a974db-ab84-457f-9ec0-55db83d7a825windows
Log Source
WindowsProcess Creation
ProductWindows← raw: windows
CategoryProcess Creation← raw: process_creation

Events generated when a new process is spawned on the system. Covers command-line arguments, parent/child relationships, and process metadata.

Detection Logic
Detection Logic1 selector
detection:
    selection:
        CommandLine|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 Script 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
92a974db-ab84-457f-9ec0-55db83d7a825
Status
test
Level
medium
Type
Detection
Created
Wed Jan 04
Modified
Tue May 09
Author
Nasreddine Bencherchali (Nextron Systems)
Path
rules/windows/process_creation/proc_creation_win_powershell_amsi_null_bits_bypass.yml
Raw Tags
attack.defense-evasionattack.t1562.001
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