from logs-windows.powershell_operational* metadata _id, _version, _index
| where event.code == "4104"

// Filter out smaller scripts that are unlikely to implement obfuscation using the patterns we are looking for
| eval Esql.script_block_length = length(powershell.file.script_block_text)
| where Esql.script_block_length > 1000

// replace the patterns we are looking for with the 🔥 emoji to enable counting them
// The emoji is used because it's unlikely to appear in scripts and has a consistent character length of 1
| eval Esql.script_block_tmp = replace(powershell.file.script_block_text, """[0-9]""", "🔥")

// count how many patterns were detected by calculating the number of 🔥 characters inserted
| eval Esql.script_block_pattern_count = Esql.script_block_length - length(replace(Esql.script_block_tmp, "🔥", ""))

// Calculate the ratio of special characters to total length
| eval Esql.script_block_ratio = Esql.script_block_pattern_count::double / Esql.script_block_length::double

// keep the fields relevant to the query, although this is not needed as the alert is populated using _id
| keep
    Esql.script_block_pattern_count,
    Esql.script_block_ratio,
    Esql.script_block_length,
    Esql.script_block_tmp,
    powershell.file.script_block_text,
    powershell.file.script_block_id,
    file.directory,
    file.path,
    powershell.sequence,
    powershell.total,
    _id,
    _index,
    host.name,
    agent.id,
    user.id

// Filter for scripts with high numeric character ratio
| where Esql.script_block_ratio > 0.30

// Exclude Windows Defender Noisy Patterns
| where not (
    file.directory == "C:\\ProgramData\\Microsoft\\Windows Defender Advanced Threat Protection\\Downloads" or
    file.directory like "C:\\\\ProgramData\\\\Microsoft\\\\Windows Defender Advanced Threat Protection\\\\DataCollection*"
  )
  // ESQL requires this condition, otherwise it only returns matches where file.directory exists.
  or file.directory is null
| where not powershell.file.script_block_text like "*[System.IO.File]::Open('C:\\\\ProgramData\\\\Microsoft\\\\Windows Defender Advanced Threat Protection\\\\DataCollection*"
| where not powershell.file.script_block_text : "26a24ae4-039d-4ca4-87b4-2f64180311f0"