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)

version: 1.0.3
tags:
- Discord
severity: Medium
queryFrequency: 1d
triggerOperator: gt
relevantTechniques:
- T1071.001
status: Available
kind: Scheduled
triggerThreshold: 0
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)  
entityMappings:
- fieldMappings:
  - columnName: SourceUser
    identifier: FullName
  entityType: Account
- fieldMappings:
  - columnName: SourceIP
    identifier: Address
  entityType: IP
- fieldMappings:
  - columnName: RequestURL
    identifier: Url
  entityType: URL
name: Discord CDN Risky File Download
queryPeriod: 1d
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'
requiredDataConnectors:
- dataTypes:
  - CommonSecurityLog
  connectorId: Zscaler
- dataTypes:
  - CommonSecurityLog
  connectorId: ZscalerAma
- dataTypes:
  - CommonSecurityLog
  connectorId: CefAma
id: 010bd98c-a6be-498c-bdcd-502308c0fdae
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Zscaler Internet Access/Analytic Rules/DiscordCDNRiskyDownload.yaml
tactics:
- CommandAndControl

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "workspace": {
      "type": "String"
    }
  },
  "resources": [
    {
      "apiVersion": "2024-01-01-preview",
      "id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/010bd98c-a6be-498c-bdcd-502308c0fdae')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/010bd98c-a6be-498c-bdcd-502308c0fdae')]",
      "properties": {
        "alertRuleTemplateName": "010bd98c-a6be-498c-bdcd-502308c0fdae",
        "customDetails": null,
        "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'\n",
        "displayName": "Discord CDN Risky File Download",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "SourceUser",
                "identifier": "FullName"
              }
            ]
          },
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "SourceIP",
                "identifier": "Address"
              }
            ]
          },
          {
            "entityType": "URL",
            "fieldMappings": [
              {
                "columnName": "RequestURL",
                "identifier": "Url"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Zscaler Internet Access/Analytic Rules/DiscordCDNRiskyDownload.yaml",
        "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",
        "severity": "Medium",
        "status": "Available",
        "subTechniques": [
          "T1071.001"
        ],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "CommandAndControl"
        ],
        "tags": [
          "Discord"
        ],
        "techniques": [
          "T1071"
        ],
        "templateVersion": "1.0.3",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}