Anthropic-Cybersecurity-Skills/skills/analyzing-powershell-script-block-logging/references/api-reference.md

API Reference: PowerShell Script Block Logging Analysis

python-evtx Library

FileHeader

from Evtx.Evtx import FileHeader
with open(evtx_path, "rb") as f:
    fh = FileHeader(f)
    for record in fh.records():
        xml_string = record.xml()  # Returns XML string of the event

Event XML Structure (Event ID 4104)

<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <EventID>4104</EventID>
    <TimeCreated SystemTime="2024-01-15T10:30:00.000Z"/>
  </System>
  <EventData>
    <Data Name="MessageNumber">1</Data>
    <Data Name="MessageTotal">3</Data>
    <Data Name="ScriptBlockText">...powershell code...</Data>
    <Data Name="ScriptBlockId">guid-string</Data>
    <Data Name="Path">C:\script.ps1</Data>
  </EventData>
</Event>

lxml etree Parsing

from lxml import etree
NS = {"evt": "http://schemas.microsoft.com/win/2004/08/events/event"}
root = etree.fromstring(xml_bytes)
event_id = root.find(".//evt:System/evt:EventID", NS).text
data_elems = root.findall(".//evt:EventData/evt:Data", NS)
for elem in data_elems:
    name = elem.get("Name")
    value = elem.text

Script Block Reconstruction

Large PowerShell scripts are split across multiple Event 4104 entries:

• ScriptBlockId: Unique GUID shared across all parts
• MessageNumber: Part index (1-based)
• MessageTotal: Total number of parts
• Reconstruct: concatenate parts ordered by MessageNumber

Key Detection Patterns

Pattern	MITRE	Risk
-EncodedCommand	T1059.001	High
FromBase64String	T1140	High
Invoke-Expression / iex	T1059.001	High
DownloadString / Net.WebClient	T1105	Critical
AmsiUtils / amsiInitFailed	T1562.001	Critical
Invoke-Mimikatz	T1003	Critical
High entropy (>5.5)	T1027	Medium