W3WP Launching Encoded Powershell

// Copyright 2025 Google LLC. Licensed under Apache-2.0.

rule ttp_windows_w3wp_launching_encoded_powershell {

  meta:
    author = "Google Cloud Security"
    rule_name = "W3WP Launching Encoded Powershell"
    description = "Detects on the execution of an encoded powershell command with a parent process of w3wp.exe."
    severity = "Medium"
    tactic = "TA0002"
    technique = "T1059.001"
    false_positives = "Legitimate administrative actions to the specified URL should be rare. Some penetration testing activity could trigger this rule. In some cases, specific third party applications could generate similar requests, but this should be rare."
    reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-49706, https://research.eye.security/sharepoint-under-siege/"
    rule_id = "mr_83daf64e-25e8-4b6b-8596-3adcc694e781"

  events:
    $e.metadata.event_type = "PROCESS_LAUNCH"
    re.regex($e.principal.process.file.full_path, `(^|\\)w3wp\.exe$`) nocase
    not re.regex($e.target.process.command_line, `\\Scripts\\CheckDiskSpace\.ps1'`) nocase
    not re.regex($e.target.process.command_line, `DQAKACQARQByAHIAbwByAEEAYwB0AGkAbwBuAFAAcgBlAGYAZQByAGUAbgBjAGUAIAA9ACAAJwBTAHQAbwBwACcADQAKAFsAdgBlAHIAcwBpAG8AbgBdACQAbQBpAG4AaQBtAHUAbQBWAGUAcgBzAGkAbwBuACAAPQAgACcAMgAuADIALgAwACcADQAKAA0ACgAkAG0AIAA9ACAASQBtAHAAbwByAHQALQBNAG8AZAB1AGwAZQAgAEEAegAuAEEAYwBjAG8AdQBuAHQAcwAg`) nocase
    not re.regex($e.target.process.command_line, `EncodedCommand JABQAG8AaQBuAHQAZQBlAFIAZQBzAG8AdQByAGMAZQBOAGEAbQBlACAAPQAgACcAVgBEAFAAUgB`) nocase
    (
      (
        re.regex($e.target.process.file.full_path, `(^|\\)(pwsh|powershell)\.exe$`) nocase and
        re.regex($e.target.process.command_line, `\s-(e|en|enc|enco|encodedcommand)\s`) nocase
      ) or
      re.regex($e.target.process.command_line, `(pwsh|powershell).*\s-(e|en|enc|enco|encodedcommand)\s`) nocase
    )

  outcome:
    $principal_hostname = $e.principal.hostname
    $risk_score = 65
    $vendor_name = array($e.metadata.vendor_name)
    $product_name = $e.metadata.product_name
    $victim_uid = $e.principal.asset.asset_id
    $victim_name = $e.principal.asset.hostname
    $victim_netid = array($e.principal.ip)
    $adversary_uid = $e.principal.user.userid
    $adversary_name = $e.principal.user.user_display_name
    $adversary_netid = $e.principal.user.windows_sid
    $tmp1 = max(
        if($e.security_result.action != "BLOCK" and $e.security_result.action != "UNKNOWN_ACTION", 2)
    )
    $tmp2 = max(
        if($e.security_result.action = "BLOCK", 1)
    )
    $result = arrays.index_to_str(strings.split("attempted,failed,succeeded,succeeded"), $tmp1 + $tmp2)
    $result_time = $e.metadata.event_timestamp.seconds
    $event_count = 1

  condition:
    $e
}