Silk Typhoon Suspicious Exchange Request

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Id	23005e87-2d3a-482b-b03d-edbebd1ae151
Rulename	Silk Typhoon Suspicious Exchange Request
Description	This query looks for suspicious request patterns to Exchange servers that fit a pattern observed by Silk Typhoon actors. The same query can be run on HTTPProxy logs from on-premise hosted Exchange servers. Reference: https://www.microsoft.com/security/blog/2021/03/02/hafnium-targeting-exchange-servers/
Severity	Medium
Tactics	InitialAccess
Techniques	T1190
Required data connectors	AzureMonitor(IIS)
Kind	Scheduled
Query frequency	1d
Query period	14d
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Detections/W3CIISLog/SilkTyphoonSuspiciousExchangeRequestPattern.yaml
Version	1.0.3
Arm template	23005e87-2d3a-482b-b03d-edbebd1ae151.json

KQL

let exchange_servers = (
W3CIISLog
| where TimeGenerated > ago(14d)
| where sSiteName =~ "Exchange Back End"
| summarize by Computer);
W3CIISLog
| where TimeGenerated > ago(1d)
| where Computer in (exchange_servers)
| where csUriQuery startswith "t="
| project-reorder TimeGenerated, Computer, csUriStem, csUriQuery, csUserName, csUserAgent, cIP
| extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))
| extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)
| extend AccountName = tostring(split(csUserName, "@")[0]), AccountUPNSuffix = tostring(split(csUserName, "@")[1])

YAML

relevantTechniques:
- T1190
name: Silk Typhoon Suspicious Exchange Request
requiredDataConnectors:
- dataTypes:
  - W3CIISLog
  connectorId: AzureMonitor(IIS)
entityMappings:
- fieldMappings:
  - identifier: FullName
    columnName: csUserName
  - identifier: Name
    columnName: AccountName
  - identifier: UPNSuffix
    columnName: AccountUPNSuffix
  entityType: Account
- fieldMappings:
  - identifier: FullName
    columnName: Computer
  - identifier: HostName
    columnName: HostName
  - identifier: NTDomain
    columnName: HostNameDomain
  entityType: Host
- fieldMappings:
  - identifier: Address
    columnName: cIP
  entityType: IP
triggerThreshold: 0
id: 23005e87-2d3a-482b-b03d-edbebd1ae151
tactics:
- InitialAccess
version: 1.0.3
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/W3CIISLog/SilkTyphoonSuspiciousExchangeRequestPattern.yaml
queryPeriod: 14d
kind: Scheduled
metadata:
  categories:
    domains:
    - Security - Threat Intelligence
  author:
    name: Microsoft Security Research
  support:
    tier: Community
  source:
    kind: Community
queryFrequency: 1d
severity: Medium
description: |
  'This query looks for suspicious request patterns to Exchange servers that fit a pattern observed by Silk Typhoon actors.
  The same query can be run on HTTPProxy logs from on-premise hosted Exchange servers.
  Reference: https://www.microsoft.com/security/blog/2021/03/02/hafnium-targeting-exchange-servers/'  
query: |
  let exchange_servers = (
  W3CIISLog
  | where TimeGenerated > ago(14d)
  | where sSiteName =~ "Exchange Back End"
  | summarize by Computer);
  W3CIISLog
  | where TimeGenerated > ago(1d)
  | where Computer in (exchange_servers)
  | where csUriQuery startswith "t="
  | project-reorder TimeGenerated, Computer, csUriStem, csUriQuery, csUserName, csUserAgent, cIP
  | extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))
  | extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)
  | extend AccountName = tostring(split(csUserName, "@")[0]), AccountUPNSuffix = tostring(split(csUserName, "@")[1])  
triggerOperator: gt

ARM

{
  "$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/23005e87-2d3a-482b-b03d-edbebd1ae151')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/23005e87-2d3a-482b-b03d-edbebd1ae151')]",
      "properties": {
        "alertRuleTemplateName": "23005e87-2d3a-482b-b03d-edbebd1ae151",
        "customDetails": null,
        "description": "'This query looks for suspicious request patterns to Exchange servers that fit a pattern observed by Silk Typhoon actors.\nThe same query can be run on HTTPProxy logs from on-premise hosted Exchange servers.\nReference: https://www.microsoft.com/security/blog/2021/03/02/hafnium-targeting-exchange-servers/'\n",
        "displayName": "Silk Typhoon Suspicious Exchange Request",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "csUserName",
                "identifier": "FullName"
              },
              {
                "columnName": "AccountName",
                "identifier": "Name"
              },
              {
                "columnName": "AccountUPNSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          },
          {
            "entityType": "Host",
            "fieldMappings": [
              {
                "columnName": "Computer",
                "identifier": "FullName"
              },
              {
                "columnName": "HostName",
                "identifier": "HostName"
              },
              {
                "columnName": "HostNameDomain",
                "identifier": "NTDomain"
              }
            ]
          },
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "cIP",
                "identifier": "Address"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Detections/W3CIISLog/SilkTyphoonSuspiciousExchangeRequestPattern.yaml",
        "query": "let exchange_servers = (\nW3CIISLog\n| where TimeGenerated > ago(14d)\n| where sSiteName =~ \"Exchange Back End\"\n| summarize by Computer);\nW3CIISLog\n| where TimeGenerated > ago(1d)\n| where Computer in (exchange_servers)\n| where csUriQuery startswith \"t=\"\n| project-reorder TimeGenerated, Computer, csUriStem, csUriQuery, csUserName, csUserAgent, cIP\n| extend HostName = tostring(split(Computer, \".\")[0]), DomainIndex = toint(indexof(Computer, '.'))\n| extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)\n| extend AccountName = tostring(split(csUserName, \"@\")[0]), AccountUPNSuffix = tostring(split(csUserName, \"@\")[1])\n",
        "queryFrequency": "P1D",
        "queryPeriod": "P14D",
        "severity": "Medium",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "InitialAccess"
        ],
        "techniques": [
          "T1190"
        ],
        "templateVersion": "1.0.3",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}