Hunt for Bad Request errors against the Groups endpoint in the Microsoft Graph API

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

rule ms_graph_group_bad_request {

  meta:
    author = "Google Cloud Security"
    description = "Identify a 400 bad request to the groups endpoint in the MS Graph API. GraphRunner's Invoke-SecurityGroupCloner function will trigger this if it fails to duplicate a group."
    rule_id = "mr_09bafa2b-5131-452c-bf5a-021063cfd5c2"
    rule_name = "Hunt for Bad Request errors against the Groups endpoint in the Microsoft Graph API"
    assumption = "This detects all web activity associated with the groups endpoint with a response code 400, normal admin actions could trigger as well. Tune using IP address ranges for admins and user agents."
    reference = "https://github.com/dafthack/GraphRunner/blob/main/GraphRunner.ps1"
    type = "Hunt"
    data_source = "MS Graph Activity Logs"
    platform = "Azure"
    severity = "Low"
    priority = "Low"

  events:
    $api.metadata.event_type = "NETWORK_HTTP"
    $api.metadata.product_event_type = "Microsoft Graph Activity"
    $api.target.url = "https://graph.microsoft.com/v1.0/groups" nocase
    $api.network.http.method = "POST"
    $api.network.http.response_code = 400

    //Can be tuned for specific User Agent strings being used
    //$api.network.http.user_agent = /PowerShell/ nocase
    //SkypeSpaces triggered during testing so filtering this out
    $api.network.http.user_agent != "SkypeSpaces/1.0a$*+"

    $api.principal.ip = $ip
    $api.network.session_id = $session

  match:
    $ip, $session over 5m

  outcome:
    $risk_score = 35
    $event_count = count_distinct($api.metadata.id)
    $requesting_user_guid = array_distinct($api.principal.user.userid)
    $requesting_ip = array_distinct($api.principal.ip)
    $user_agent = array_distinct($api.network.http.user_agent)
    $location = array_distinct($api.principal.location.name)
    $target_application_id_guid = array_distinct($api.target.resource.product_object_id)
    $session_id = array_distinct($api.network.session_id)
    $target_url = array_distinct($api.target.url)

  condition:
    $api
}