Suspicious link sharing pattern

let threshold = 3;
ZoomLogs
| where Event =~ "chat_message.sent"
| extend Channel = tostring(parse_json(ChatEvents).Channel)
| extend Message = tostring(parse_json(ChatEvents).Message)
| where Message matches regex "http(s?):\\/\\/"
| summarize Channels = makeset(Channel), StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by Message, User, UserId
| extend ChannelCount = arraylength(Channels)
| where ChannelCount > threshold
| extend AccountName = tostring(split(User, "@")[0]), AccountUPNSuffix = tostring(split(User, "@")[1])

relevantTechniques:
- T1598
name: Suspicious link sharing pattern
requiredDataConnectors: []
entityMappings:
- fieldMappings:
  - identifier: FullName
    columnName: User
  - identifier: Name
    columnName: AccountName
  - identifier: UPNSuffix
    columnName: AccountUPNSuffix
  entityType: Account
triggerThreshold: 0
id: 1218175f-c534-421c-8070-5dcaabf28067
tactics:
- Reconnaissance
version: 1.0.4
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/ZoomLogs/SupiciousLinkSharing.yaml
queryPeriod: 1d
kind: Scheduled
metadata:
  categories:
    domains:
    - Security - Others
  author:
    name: Microsoft Security Research
  support:
    tier: Community
  source:
    kind: Community
queryFrequency: 1d
severity: Low
description: |
  'Alerts in links that have been shared across multiple Zoom chat channels by the same user in a short space if time.
  Adjust the threshold figure to change the number of channels a message needs to be posted in before an alert is raised.'  
query: |
  let threshold = 3;
  ZoomLogs
  | where Event =~ "chat_message.sent"
  | extend Channel = tostring(parse_json(ChatEvents).Channel)
  | extend Message = tostring(parse_json(ChatEvents).Message)
  | where Message matches regex "http(s?):\\/\\/"
  | summarize Channels = makeset(Channel), StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by Message, User, UserId
  | extend ChannelCount = arraylength(Channels)
  | where ChannelCount > threshold
  | extend AccountName = tostring(split(User, "@")[0]), AccountUPNSuffix = tostring(split(User, "@")[1])  
triggerOperator: gt

{
  "$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/1218175f-c534-421c-8070-5dcaabf28067')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/1218175f-c534-421c-8070-5dcaabf28067')]",
      "properties": {
        "alertRuleTemplateName": "1218175f-c534-421c-8070-5dcaabf28067",
        "customDetails": null,
        "description": "'Alerts in links that have been shared across multiple Zoom chat channels by the same user in a short space if time.\nAdjust the threshold figure to change the number of channels a message needs to be posted in before an alert is raised.'\n",
        "displayName": "Suspicious link sharing pattern",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "User",
                "identifier": "FullName"
              },
              {
                "columnName": "AccountName",
                "identifier": "Name"
              },
              {
                "columnName": "AccountUPNSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Detections/ZoomLogs/SupiciousLinkSharing.yaml",
        "query": "let threshold = 3;\nZoomLogs\n| where Event =~ \"chat_message.sent\"\n| extend Channel = tostring(parse_json(ChatEvents).Channel)\n| extend Message = tostring(parse_json(ChatEvents).Message)\n| where Message matches regex \"http(s?):\\\\/\\\\/\"\n| summarize Channels = makeset(Channel), StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by Message, User, UserId\n| extend ChannelCount = arraylength(Channels)\n| where ChannelCount > threshold\n| extend AccountName = tostring(split(User, \"@\")[0]), AccountUPNSuffix = tostring(split(User, \"@\")[1])\n",
        "queryFrequency": "P1D",
        "queryPeriod": "P1D",
        "severity": "Low",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "Reconnaissance"
        ],
        "techniques": [
          "T1598"
        ],
        "templateVersion": "1.0.4",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}