Suspicious Invoke-WebRequest Execution

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 * Copyright 2025 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

rule suspicious_invoke_webrequest_execution {

  meta:
    author = "Nasreddine Bencherchali (Nextron Systems)"
    description = "Detects a suspicious call to Invoke-WebRequest cmdlet where the and output is located in a suspicious location"
    reference = "https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_powershell_invoke_webrequest_download.yml"
    license = "https://github.com/SigmaHQ/Detection-Rule-License/blob/main/LICENSE.Detection.Rules.md"
    rule_name = "Suspicious Invoke-WebRequest Execution"
    sigma_uuid = "5e3cc4d8-3e68-43db-8656-eaaeefdec9cc"
    sigma_status = "test"
    rule_id = "mr_62fb3b3f-e99f-4ab3-9d5b-21994ba25ebe"
    tactic = "TA0011"
    technique = "T1105"
    type = "Detection"
    data_source = "Sysmon"
    platform = "Windows"
    severity = "High"
    priority = "High"
    false_positives = "Unknown"

 events:
   $process.metadata.event_type = "PROCESS_LAUNCH"
   (
       re.regex($process.target.process.file.full_path, `\\powershell\.exe$`) nocase or
       re.regex($process.target.process.file.full_path, `\\pwsh\.exe$`) nocase or
       $process.src.process.file.full_path = "powershell.exe" nocase or
       $process.src.process.file.full_path = "pwsh.dll" nocase
   )
   (
       strings.contains(strings.to_lower($process.target.process.command_line), "curl ") or
       strings.contains(strings.to_lower($process.target.process.command_line), "invoke-webrequest") or
       strings.contains(strings.to_lower($process.target.process.command_line), "iwr ") or
       strings.contains(strings.to_lower($process.target.process.command_line), "wget ")
   )
   (
       strings.contains(strings.to_lower($process.target.process.command_line), " -ur") or
       strings.contains(strings.to_lower($process.target.process.command_line), " -o")
   )
   (
       strings.contains(strings.to_lower($process.target.process.command_line), "\\appdata\\") or
       strings.contains(strings.to_lower($process.target.process.command_line), "\\desktop\\") or
       strings.contains(strings.to_lower($process.target.process.command_line), "\\temp\\") or
       strings.contains(strings.to_lower($process.target.process.command_line), "\\users\\public\\") or
       strings.contains(strings.to_lower($process.target.process.command_line), "%appdata%") or
       strings.contains(strings.to_lower($process.target.process.command_line), "%public%") or
       strings.contains(strings.to_lower($process.target.process.command_line), "%temp%") or
       strings.contains(strings.to_lower($process.target.process.command_line), "%tmp%") or
       strings.contains(strings.to_lower($process.target.process.command_line), ":\\windows\\")
   )
   $process.principal.hostname = $hostname

 match:
   $hostname over 5m

 outcome:
    //example usage of specifying test user and hostname to adjust risk score
    $risk_score = max(if($process.principal.user.userid = "user" and $process.principal.hostname = "hostname", 0, 15))
    $principal_process_pid = array_distinct($process.principal.process.pid)
    $principal_process_command_line = array_distinct($process.principal.process.command_line)
    $principal_process_file_sha256 = array_distinct($process.principal.process.file.sha256)
    $principal_process_file_full_path = array_distinct($process.principal.process.file.full_path)
    $principal_process_product_specfic_process_id = array_distinct($process.principal.process.product_specific_process_id)
    $principal_process_parent_process_product_specfic_process_id = array_distinct($process.principal.process.parent_process.product_specific_process_id)
    $target_process_pid = array_distinct($process.target.process.pid)
    $target_process_command_line = array_distinct($process.target.process.command_line)
    $target_process_file_sha256 = array_distinct($process.target.process.file.sha256)
    $target_process_file_full_path = array_distinct($process.target.process.file.full_path)
    $target_process_product_specfic_process_id = array_distinct($process.target.process.product_specific_process_id)
    $principal_user_userid = array_distinct($process.principal.user.userid)
    $log_type = array_distinct(strings.concat($process.metadata.log_type,"/",$process.metadata.product_event_type))

 condition:
   $process
}