Discord CDN Risky File Download

let connectionThreshold = 1;
let riskyExtensions = dynamic([".bin",".exe",".dll",".bin",".msi"]);
CommonSecurityLog
| where DeviceVendor =~ "ZScaler"
| where RequestURL has_any("media.discordapp.net", "cdn.discordapp.com")
| where RequestURL has "attachments"
| where DeviceAction !~ "blocked"
| extend DiscordServerId = extract(@"\/attachments\/([0-9]+)\/", 1, RequestURL)
| summarize dcount(RequestURL), make_set(SourceUserName), make_set(SourceIP), make_set(RequestURL), min(TimeGenerated), max(TimeGenerated), make_set(DeviceAction) by DiscordServerId, DeviceProduct
| where dcount_RequestURL <= connectionThreshold
| mv-expand set_SourceUserName to typeof(string), set_RequestURL to typeof(string), set_DeviceAction to typeof(string), set_SourceIP to typeof(string)
| summarize by DiscordServerId, DeviceProduct, dcount_RequestURL, set_SourceUserName, min_TimeGenerated, max_TimeGenerated, set_DeviceAction, set_SourceIP, set_RequestURL
| project StartTime=min_TimeGenerated, EndTime=max_TimeGenerated, DeviceActionTaken=set_DeviceAction, DeviceProduct, SourceUser=set_SourceUserName, SourceIP=set_SourceIP, RequestURL=set_RequestURL
| where RequestURL has_any (riskyExtensions)

severity: Medium
queryFrequency: 1d
relevantTechniques:
- T1071.001
tactics:
- CommandAndControl
kind: Scheduled
query: |
  let connectionThreshold = 1;
  let riskyExtensions = dynamic([".bin",".exe",".dll",".bin",".msi"]);
  CommonSecurityLog
  | where DeviceVendor =~ "ZScaler"
  | where RequestURL has_any("media.discordapp.net", "cdn.discordapp.com")
  | where RequestURL has "attachments"
  | where DeviceAction !~ "blocked"
  | extend DiscordServerId = extract(@"\/attachments\/([0-9]+)\/", 1, RequestURL)
  | summarize dcount(RequestURL), make_set(SourceUserName), make_set(SourceIP), make_set(RequestURL), min(TimeGenerated), max(TimeGenerated), make_set(DeviceAction) by DiscordServerId, DeviceProduct
  | where dcount_RequestURL <= connectionThreshold
  | mv-expand set_SourceUserName to typeof(string), set_RequestURL to typeof(string), set_DeviceAction to typeof(string), set_SourceIP to typeof(string)
  | summarize by DiscordServerId, DeviceProduct, dcount_RequestURL, set_SourceUserName, min_TimeGenerated, max_TimeGenerated, set_DeviceAction, set_SourceIP, set_RequestURL
  | project StartTime=min_TimeGenerated, EndTime=max_TimeGenerated, DeviceActionTaken=set_DeviceAction, DeviceProduct, SourceUser=set_SourceUserName, SourceIP=set_SourceIP, RequestURL=set_RequestURL
  | where RequestURL has_any (riskyExtensions)  
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Zscaler Internet Access/Analytic Rules/DiscordCDNRiskyDownload.yaml
queryPeriod: 1d
status: Available
version: 1.0.0
tags:
- Discord
name: Discord CDN Risky File Download
requiredDataConnectors:
- dataTypes:
  - CommonSecurityLog
  connectorId: Zscaler
triggerOperator: gt
entityMappings:
- entityType: Account
  fieldMappings:
  - identifier: FullName
    columnName: SourceUser
- entityType: IP
  fieldMappings:
  - identifier: Address
    columnName: SourceIP
- entityType: URL
  fieldMappings:
  - identifier: Url
    columnName: RequestURL
id: 010bd98c-a6be-498c-bdcd-502308c0fdae
description: |
  'Identifies callouts to Discord CDN addresses for risky file extensions. This detection will trigger when a callout for a risky file
  is made to a discord server that has only been seen once in your environment. Unique discord servers are identified using the server ID
  that is included in the request URL (DiscordServerId in query). Discord CDN has been used in multiple campaigns to download additional payloads'  
triggerThreshold: 0

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "workspace": {
      "type": "String"
    }
  },
  "resources": [
    {
      "id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/010bd98c-a6be-498c-bdcd-502308c0fdae')]",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/010bd98c-a6be-498c-bdcd-502308c0fdae')]",
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules",
      "kind": "Scheduled",
      "apiVersion": "2022-11-01-preview",
      "properties": {
        "displayName": "Discord CDN Risky File Download",
        "description": "'Identifies callouts to Discord CDN addresses for risky file extensions. This detection will trigger when a callout for a risky file\nis made to a discord server that has only been seen once in your environment. Unique discord servers are identified using the server ID\nthat is included in the request URL (DiscordServerId in query). Discord CDN has been used in multiple campaigns to download additional payloads'\n",
        "severity": "Medium",
        "enabled": true,
        "query": "let connectionThreshold = 1;\nlet riskyExtensions = dynamic([\".bin\",\".exe\",\".dll\",\".bin\",\".msi\"]);\nCommonSecurityLog\n| where DeviceVendor =~ \"ZScaler\"\n| where RequestURL has_any(\"media.discordapp.net\", \"cdn.discordapp.com\")\n| where RequestURL has \"attachments\"\n| where DeviceAction !~ \"blocked\"\n| extend DiscordServerId = extract(@\"\\/attachments\\/([0-9]+)\\/\", 1, RequestURL)\n| summarize dcount(RequestURL), make_set(SourceUserName), make_set(SourceIP), make_set(RequestURL), min(TimeGenerated), max(TimeGenerated), make_set(DeviceAction) by DiscordServerId, DeviceProduct\n| where dcount_RequestURL <= connectionThreshold\n| mv-expand set_SourceUserName to typeof(string), set_RequestURL to typeof(string), set_DeviceAction to typeof(string), set_SourceIP to typeof(string)\n| summarize by DiscordServerId, DeviceProduct, dcount_RequestURL, set_SourceUserName, min_TimeGenerated, max_TimeGenerated, set_DeviceAction, set_SourceIP, set_RequestURL\n| project StartTime=min_TimeGenerated, EndTime=max_TimeGenerated, DeviceActionTaken=set_DeviceAction, DeviceProduct, SourceUser=set_SourceUserName, SourceIP=set_SourceIP, RequestURL=set_RequestURL\n| where RequestURL has_any (riskyExtensions)\n",
        "queryFrequency": "P1D",
        "queryPeriod": "P1D",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0,
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "CommandAndControl"
        ],
        "techniques": [
          "T1071.001"
        ],
        "alertRuleTemplateName": "010bd98c-a6be-498c-bdcd-502308c0fdae",
        "customDetails": null,
        "entityMappings": [
          {
            "fieldMappings": [
              {
                "columnName": "SourceUser",
                "identifier": "FullName"
              }
            ],
            "entityType": "Account"
          },
          {
            "fieldMappings": [
              {
                "columnName": "SourceIP",
                "identifier": "Address"
              }
            ],
            "entityType": "IP"
          },
          {
            "fieldMappings": [
              {
                "columnName": "RequestURL",
                "identifier": "Url"
              }
            ],
            "entityType": "URL"
          }
        ],
        "tags": [
          "Discord"
        ],
        "status": "Available",
        "templateVersion": "1.0.0",
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Zscaler Internet Access/Analytic Rules/DiscordCDNRiskyDownload.yaml"
      }
    }
  ]
}