Discord CDN Risky File Download ASIM Web Session Schema

let discord=dynamic(["cdn.discordapp.com", "media.discordapp.com"]);
  _Im_WebSession(url_has_any=discord, eventresult='Success')
  | where Url has "attachments"
  | extend DiscordServerId = extract(@"\/attachments\/([0-9]+)\/", 1, Url)
  | summarize dcount(Url), make_set(SrcUsername), make_set(SrcIpAddr), make_set(Url), min(TimeGenerated), max(TimeGenerated), make_set(EventResult) by DiscordServerId
  | mv-expand set_SrcUsername to typeof(string), set_Url to typeof(string), set_EventResult to typeof(string), set_SrcIpAddr to typeof(string)
  | summarize by DiscordServerId, dcount_Url, set_SrcUsername, min_TimeGenerated, max_TimeGenerated, set_EventResult, set_SrcIpAddr, set_Url
  | project StartTime=min_TimeGenerated, EndTime=max_TimeGenerated, Result=set_EventResult, SourceUser=set_SrcUsername, SourceIP=set_SrcIpAddr, RequestURL=set_Url
  | where RequestURL has_any (".bin",".exe",".dll",".bin",".msi")
  | extend AccountName = tostring(split(SourceUser, "@")[0]), AccountUPNSuffix = tostring(split(SourceUser, "@")[1])

OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/ASimWebSession/DiscordCDNRiskyFileDownload_ASim.yaml
query: |
  let discord=dynamic(["cdn.discordapp.com", "media.discordapp.com"]);
    _Im_WebSession(url_has_any=discord, eventresult='Success')
    | where Url has "attachments"
    | extend DiscordServerId = extract(@"\/attachments\/([0-9]+)\/", 1, Url)
    | summarize dcount(Url), make_set(SrcUsername), make_set(SrcIpAddr), make_set(Url), min(TimeGenerated), max(TimeGenerated), make_set(EventResult) by DiscordServerId
    | mv-expand set_SrcUsername to typeof(string), set_Url to typeof(string), set_EventResult to typeof(string), set_SrcIpAddr to typeof(string)
    | summarize by DiscordServerId, dcount_Url, set_SrcUsername, min_TimeGenerated, max_TimeGenerated, set_EventResult, set_SrcIpAddr, set_Url
    | project StartTime=min_TimeGenerated, EndTime=max_TimeGenerated, Result=set_EventResult, SourceUser=set_SrcUsername, SourceIP=set_SrcIpAddr, RequestURL=set_Url
    | where RequestURL has_any (".bin",".exe",".dll",".bin",".msi")
    | extend AccountName = tostring(split(SourceUser, "@")[0]), AccountUPNSuffix = tostring(split(SourceUser, "@")[1])  
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.
   This analytic rule uses [ASIM](https://aka.ms/AboutASIM) and supports any built-in or custom source that supports the ASIM WebSession schema (ASIM WebSession Schema)'  
severity: Medium
requiredDataConnectors:
- dataTypes:
  - SquidProxy_CL
  connectorId: SquidProxy
- dataTypes:
  - CommonSecurityLog
  connectorId: Zscaler
tags:
- Discord
triggerThreshold: 0
metadata:
  source:
    kind: Community
  categories:
    domains:
    - Security - Threat Protection
  author:
    name: Microsoft Security Research
  support:
    tier: Community
entityMappings:
- entityType: Account
  fieldMappings:
  - columnName: SourceUser
    identifier: FullName
  - columnName: AccountName
    identifier: Name
  - columnName: AccountUPNSuffix
    identifier: UPNSuffix
- entityType: IP
  fieldMappings:
  - columnName: SourceIP
    identifier: Address
- entityType: URL
  fieldMappings:
  - columnName: RequestURL
    identifier: Url
tactics:
- CommandAndControl
version: 1.1.4
relevantTechniques:
- T1071.001
triggerOperator: gt
name: Discord CDN Risky File Download  (ASIM Web Session Schema)
id: 01e8ffff-dc0c-43fe-aa22-d459c4204553
kind: Scheduled
queryFrequency: 1d
queryPeriod: 1d

{
  "$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/01e8ffff-dc0c-43fe-aa22-d459c4204553')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/01e8ffff-dc0c-43fe-aa22-d459c4204553')]",
      "properties": {
        "alertRuleTemplateName": "01e8ffff-dc0c-43fe-aa22-d459c4204553",
        "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. \n 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 This analytic rule uses [ASIM](https://aka.ms/AboutASIM) and supports any built-in or custom source that supports the ASIM WebSession schema (ASIM WebSession Schema)'\n",
        "displayName": "Discord CDN Risky File Download  (ASIM Web Session Schema)",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "SourceUser",
                "identifier": "FullName"
              },
              {
                "columnName": "AccountName",
                "identifier": "Name"
              },
              {
                "columnName": "AccountUPNSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          },
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "SourceIP",
                "identifier": "Address"
              }
            ]
          },
          {
            "entityType": "URL",
            "fieldMappings": [
              {
                "columnName": "RequestURL",
                "identifier": "Url"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Detections/ASimWebSession/DiscordCDNRiskyFileDownload_ASim.yaml",
        "query": "let discord=dynamic([\"cdn.discordapp.com\", \"media.discordapp.com\"]);\n  _Im_WebSession(url_has_any=discord, eventresult='Success')\n  | where Url has \"attachments\"\n  | extend DiscordServerId = extract(@\"\\/attachments\\/([0-9]+)\\/\", 1, Url)\n  | summarize dcount(Url), make_set(SrcUsername), make_set(SrcIpAddr), make_set(Url), min(TimeGenerated), max(TimeGenerated), make_set(EventResult) by DiscordServerId\n  | mv-expand set_SrcUsername to typeof(string), set_Url to typeof(string), set_EventResult to typeof(string), set_SrcIpAddr to typeof(string)\n  | summarize by DiscordServerId, dcount_Url, set_SrcUsername, min_TimeGenerated, max_TimeGenerated, set_EventResult, set_SrcIpAddr, set_Url\n  | project StartTime=min_TimeGenerated, EndTime=max_TimeGenerated, Result=set_EventResult, SourceUser=set_SrcUsername, SourceIP=set_SrcIpAddr, RequestURL=set_Url\n  | where RequestURL has_any (\".bin\",\".exe\",\".dll\",\".bin\",\".msi\")\n  | extend AccountName = tostring(split(SourceUser, \"@\")[0]), AccountUPNSuffix = tostring(split(SourceUser, \"@\")[1])\n",
        "queryFrequency": "P1D",
        "queryPeriod": "P1D",
        "severity": "Medium",
        "subTechniques": [
          "T1071.001"
        ],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "CommandAndControl"
        ],
        "tags": [
          "Discord"
        ],
        "techniques": [
          "T1071"
        ],
        "templateVersion": "1.1.4",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}