Microsoft Sentinel Analytic Rules
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Detect presence of uncommon user agents in web requests ASIM Web Session

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Id2d50d937-d7f2-4c05-b151-9af7f9ec747e
RulenameDetect presence of uncommon user agents in web requests (ASIM Web Session)
DescriptionThis rule assists in detecting rare user agents, which may indicate web browsing activity by an unconventional process different from the usual ones. The rule specifically searches for UserAgent strings that have not been seen in the past 14 days. This query will perform better when run over summarized data
SeverityMedium
TacticsInitialAccess
TechniquesT1190
T1133
KindScheduled
Query frequency1h
Query period14d
Trigger threshold0
Trigger operatorgt
Source Urihttps://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Web Session Essentials/Analytic Rules/RareUserAgentDetected.yaml
Version1.0.1
Arm template2d50d937-d7f2-4c05-b151-9af7f9ec747e.json
Deploy To Azure
let lookBack = 14d;
let timeframe = 1h;
// calculate avg. eps(events per second)
let eps = materialize(_Im_WebSession(starttime=ago(1d))
    | project TimeGenerated
    | summarize AvgPerSec = count() / 3600 by bin(TimeGenerated, 1h)
    | summarize round(avg(AvgPerSec))
    );
let summarizationexist  = (
    union isfuzzy=true 
        (
        WebSession_Summarized_SrcInfo_CL
        | where EventTime_t > ago(1d) 
        | project v = int(2)
        ),
        (
        print int(1) 
        | project v = print_0
        )
    | summarize maxv = max(v)
    | extend sumexist = (maxv > 1)
    );
let allUserAgents = union isfuzzy=true
        (
        (datatable(exists: int, sumexist: bool)[1, false]
        | where toscalar(eps) > 1000
        | join (summarizationexist) on sumexist)
        | join (
            _Im_WebSession(starttime=todatetime(ago(2d)), endtime=bin(ago(timeframe), 1h), eventresult='Success')
            | where isnotempty(HttpUserAgent)
            | summarize UserAgentsSet =  make_set(HttpUserAgent) // This could contain upto 10,48,576 unique values
            | extend exists=int(1)
            )
            on exists
        | project-away exist*, maxv, sum*
        ),
        (
        (datatable(exists: int, sumexist: bool)[1, false]
        | where toscalar(eps) between (501 .. 1000)
        | join (summarizationexist) on sumexist)
        | join (
            _Im_WebSession(starttime=todatetime(ago(3d)), endtime=bin(ago(timeframe), 1h), eventresult='Success')
            | where isnotempty(HttpUserAgent)
            | summarize UserAgentsSet = make_set(HttpUserAgent) // This could contain upto 10,48,576 unique values
            | extend exists=int(1)
            )
            on exists
        | project-away exist*, maxv, sum*
        ),
        (
        (datatable(exists: int, sumexist: bool)[1, false]
        | where toscalar(eps) <= 500
        | join (summarizationexist) on sumexist)
        | join (
            _Im_WebSession(starttime=todatetime(ago(4d)), endtime=bin(ago(timeframe), 1h), eventresult='Success')
            | where isnotempty(HttpUserAgent)
            | summarize UserAgentsSet = make_set(HttpUserAgent) // This could contain upto 10,48,576 unique values
            | extend exists=int(1)
            )
            on exists
        | project-away exist*, maxv, sum*
        ),
        (
        WebSession_Summarized_SrcInfo_CL
        | where EventTime_t between (ago(14d) .. ago(timeframe))
            and isnotempty(HttpUserAgent_s)
            and EventResult_s =~ 'Success'
        | summarize UserAgentsSet = make_set(HttpUserAgent_s) // This could contain upto 10,48,576 unique values
        );
_Im_WebSession (starttime=bin(ago(timeframe), 1h), eventresult='Success')
| project
    SrcIpAddr,
    SrcUsername,
    SrcHostname,
    DstIpAddr,
    DstPortNumber,
    Url,
    HttpUserAgent,
    TimeGenerated
| where isnotempty(HttpUserAgent) and HttpUserAgent !in~ (allUserAgents)
| summarize
    EventCount=count(),
    EventStartTime=min(TimeGenerated),
    EventEndTime=max(TimeGenerated)
    by
    SrcIpAddr,
    SrcUsername,
    SrcHostname,
    DstIpAddr,
    Url,
    HttpUserAgent,
    DstPortNumber
| extend Name = iif(SrcUsername contains "@", tostring(split(SrcUsername,'@',0)[0]),SrcUsername), UPNSuffix = iif(SrcUsername contains "@",tostring(split(SrcUsername,'@',1)[0]),"")
status: Available
id: 2d50d937-d7f2-4c05-b151-9af7f9ec747e
name: Detect presence of uncommon user agents in web requests (ASIM Web Session)
customDetails:
  HttpUserAgent: HttpUserAgent
  EventStartTime: EventStartTime
  EventEndTime: EventEndTime
  EventCount: EventCount
  DstPortNumber: DstPortNumber
kind: Scheduled
requiredDataConnectors: []
alertDetailsOverride:
  alertDisplayNameFormat: User '{{SrcUsername}}' with IP '{{SrcIpAddr}}' has been observed accessing URL '{{Url}}' using a rare user agent.
  alertDescriptionFormat: The user agent '{{HttpUserAgent}}' has not been observed in the past 14 days. Conduct research on the user agent string to determine if it is associated with a known legitimate bot or if it is potentially linked to malicious activity. The URL is associated with the IP address '{{DstIpAddr}}'.
severity: Medium
triggerThreshold: 0
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Web Session Essentials/Analytic Rules/RareUserAgentDetected.yaml
tags:
- Schema: WebSession
  SchemaVersion: 0.2.6
description: |
    'This rule assists in detecting rare user agents, which may indicate web browsing activity by an unconventional process different from the usual ones. The rule specifically searches for UserAgent strings that have not been seen in the past 14 days. This query will perform better when run over summarized data'
relevantTechniques:
- T1190
- T1133
eventGroupingSettings:
  aggregationKind: AlertPerResult
queryPeriod: 14d
triggerOperator: gt
queryFrequency: 1h
query: |
  let lookBack = 14d;
  let timeframe = 1h;
  // calculate avg. eps(events per second)
  let eps = materialize(_Im_WebSession(starttime=ago(1d))
      | project TimeGenerated
      | summarize AvgPerSec = count() / 3600 by bin(TimeGenerated, 1h)
      | summarize round(avg(AvgPerSec))
      );
  let summarizationexist  = (
      union isfuzzy=true 
          (
          WebSession_Summarized_SrcInfo_CL
          | where EventTime_t > ago(1d) 
          | project v = int(2)
          ),
          (
          print int(1) 
          | project v = print_0
          )
      | summarize maxv = max(v)
      | extend sumexist = (maxv > 1)
      );
  let allUserAgents = union isfuzzy=true
          (
          (datatable(exists: int, sumexist: bool)[1, false]
          | where toscalar(eps) > 1000
          | join (summarizationexist) on sumexist)
          | join (
              _Im_WebSession(starttime=todatetime(ago(2d)), endtime=bin(ago(timeframe), 1h), eventresult='Success')
              | where isnotempty(HttpUserAgent)
              | summarize UserAgentsSet =  make_set(HttpUserAgent) // This could contain upto 10,48,576 unique values
              | extend exists=int(1)
              )
              on exists
          | project-away exist*, maxv, sum*
          ),
          (
          (datatable(exists: int, sumexist: bool)[1, false]
          | where toscalar(eps) between (501 .. 1000)
          | join (summarizationexist) on sumexist)
          | join (
              _Im_WebSession(starttime=todatetime(ago(3d)), endtime=bin(ago(timeframe), 1h), eventresult='Success')
              | where isnotempty(HttpUserAgent)
              | summarize UserAgentsSet = make_set(HttpUserAgent) // This could contain upto 10,48,576 unique values
              | extend exists=int(1)
              )
              on exists
          | project-away exist*, maxv, sum*
          ),
          (
          (datatable(exists: int, sumexist: bool)[1, false]
          | where toscalar(eps) <= 500
          | join (summarizationexist) on sumexist)
          | join (
              _Im_WebSession(starttime=todatetime(ago(4d)), endtime=bin(ago(timeframe), 1h), eventresult='Success')
              | where isnotempty(HttpUserAgent)
              | summarize UserAgentsSet = make_set(HttpUserAgent) // This could contain upto 10,48,576 unique values
              | extend exists=int(1)
              )
              on exists
          | project-away exist*, maxv, sum*
          ),
          (
          WebSession_Summarized_SrcInfo_CL
          | where EventTime_t between (ago(14d) .. ago(timeframe))
              and isnotempty(HttpUserAgent_s)
              and EventResult_s =~ 'Success'
          | summarize UserAgentsSet = make_set(HttpUserAgent_s) // This could contain upto 10,48,576 unique values
          );
  _Im_WebSession (starttime=bin(ago(timeframe), 1h), eventresult='Success')
  | project
      SrcIpAddr,
      SrcUsername,
      SrcHostname,
      DstIpAddr,
      DstPortNumber,
      Url,
      HttpUserAgent,
      TimeGenerated
  | where isnotempty(HttpUserAgent) and HttpUserAgent !in~ (allUserAgents)
  | summarize
      EventCount=count(),
      EventStartTime=min(TimeGenerated),
      EventEndTime=max(TimeGenerated)
      by
      SrcIpAddr,
      SrcUsername,
      SrcHostname,
      DstIpAddr,
      Url,
      HttpUserAgent,
      DstPortNumber
  | extend Name = iif(SrcUsername contains "@", tostring(split(SrcUsername,'@',0)[0]),SrcUsername), UPNSuffix = iif(SrcUsername contains "@",tostring(split(SrcUsername,'@',1)[0]),"")  
version: 1.0.1
tactics:
- InitialAccess
entityMappings:
- fieldMappings:
  - identifier: Url
    columnName: Url
  entityType: URL
- fieldMappings:
  - identifier: Address
    columnName: SrcIpAddr
  entityType: IP
- fieldMappings:
  - identifier: Address
    columnName: DstIpAddr
  entityType: IP
- fieldMappings:
  - identifier: Name
    columnName: Name
  - identifier: UPNSuffix
    columnName: UPNSuffix
  entityType: Account
- fieldMappings:
  - identifier: HostName
    columnName: SrcHostname
  entityType: Host
{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "workspace": {
      "type": "String"
    }
  },
  "resources": [
    {
      "apiVersion": "2023-02-01-preview",
      "id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/2d50d937-d7f2-4c05-b151-9af7f9ec747e')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/2d50d937-d7f2-4c05-b151-9af7f9ec747e')]",
      "properties": {
        "alertDetailsOverride": {
          "alertDescriptionFormat": "The user agent '{{HttpUserAgent}}' has not been observed in the past 14 days. Conduct research on the user agent string to determine if it is associated with a known legitimate bot or if it is potentially linked to malicious activity. The URL is associated with the IP address '{{DstIpAddr}}'.",
          "alertDisplayNameFormat": "User '{{SrcUsername}}' with IP '{{SrcIpAddr}}' has been observed accessing URL '{{Url}}' using a rare user agent."
        },
        "alertRuleTemplateName": "2d50d937-d7f2-4c05-b151-9af7f9ec747e",
        "customDetails": {
          "DstPortNumber": "DstPortNumber",
          "EventCount": "EventCount",
          "EventEndTime": "EventEndTime",
          "EventStartTime": "EventStartTime",
          "HttpUserAgent": "HttpUserAgent"
        },
        "description": "'This rule assists in detecting rare user agents, which may indicate web browsing activity by an unconventional process different from the usual ones. The rule specifically searches for UserAgent strings that have not been seen in the past 14 days. This query will perform better when run over summarized data'\n",
        "displayName": "Detect presence of uncommon user agents in web requests (ASIM Web Session)",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "URL",
            "fieldMappings": [
              {
                "columnName": "Url",
                "identifier": "Url"
              }
            ]
          },
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "SrcIpAddr",
                "identifier": "Address"
              }
            ]
          },
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "DstIpAddr",
                "identifier": "Address"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "Name",
                "identifier": "Name"
              },
              {
                "columnName": "UPNSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          },
          {
            "entityType": "Host",
            "fieldMappings": [
              {
                "columnName": "SrcHostname",
                "identifier": "HostName"
              }
            ]
          }
        ],
        "eventGroupingSettings": {
          "aggregationKind": "AlertPerResult"
        },
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Web Session Essentials/Analytic Rules/RareUserAgentDetected.yaml",
        "query": "let lookBack = 14d;\nlet timeframe = 1h;\n// calculate avg. eps(events per second)\nlet eps = materialize(_Im_WebSession(starttime=ago(1d))\n    | project TimeGenerated\n    | summarize AvgPerSec = count() / 3600 by bin(TimeGenerated, 1h)\n    | summarize round(avg(AvgPerSec))\n    );\nlet summarizationexist  = (\n    union isfuzzy=true \n        (\n        WebSession_Summarized_SrcInfo_CL\n        | where EventTime_t > ago(1d) \n        | project v = int(2)\n        ),\n        (\n        print int(1) \n        | project v = print_0\n        )\n    | summarize maxv = max(v)\n    | extend sumexist = (maxv > 1)\n    );\nlet allUserAgents = union isfuzzy=true\n        (\n        (datatable(exists: int, sumexist: bool)[1, false]\n        | where toscalar(eps) > 1000\n        | join (summarizationexist) on sumexist)\n        | join (\n            _Im_WebSession(starttime=todatetime(ago(2d)), endtime=bin(ago(timeframe), 1h), eventresult='Success')\n            | where isnotempty(HttpUserAgent)\n            | summarize UserAgentsSet =  make_set(HttpUserAgent) // This could contain upto 10,48,576 unique values\n            | extend exists=int(1)\n            )\n            on exists\n        | project-away exist*, maxv, sum*\n        ),\n        (\n        (datatable(exists: int, sumexist: bool)[1, false]\n        | where toscalar(eps) between (501 .. 1000)\n        | join (summarizationexist) on sumexist)\n        | join (\n            _Im_WebSession(starttime=todatetime(ago(3d)), endtime=bin(ago(timeframe), 1h), eventresult='Success')\n            | where isnotempty(HttpUserAgent)\n            | summarize UserAgentsSet = make_set(HttpUserAgent) // This could contain upto 10,48,576 unique values\n            | extend exists=int(1)\n            )\n            on exists\n        | project-away exist*, maxv, sum*\n        ),\n        (\n        (datatable(exists: int, sumexist: bool)[1, false]\n        | where toscalar(eps) <= 500\n        | join (summarizationexist) on sumexist)\n        | join (\n            _Im_WebSession(starttime=todatetime(ago(4d)), endtime=bin(ago(timeframe), 1h), eventresult='Success')\n            | where isnotempty(HttpUserAgent)\n            | summarize UserAgentsSet = make_set(HttpUserAgent) // This could contain upto 10,48,576 unique values\n            | extend exists=int(1)\n            )\n            on exists\n        | project-away exist*, maxv, sum*\n        ),\n        (\n        WebSession_Summarized_SrcInfo_CL\n        | where EventTime_t between (ago(14d) .. ago(timeframe))\n            and isnotempty(HttpUserAgent_s)\n            and EventResult_s =~ 'Success'\n        | summarize UserAgentsSet = make_set(HttpUserAgent_s) // This could contain upto 10,48,576 unique values\n        );\n_Im_WebSession (starttime=bin(ago(timeframe), 1h), eventresult='Success')\n| project\n    SrcIpAddr,\n    SrcUsername,\n    SrcHostname,\n    DstIpAddr,\n    DstPortNumber,\n    Url,\n    HttpUserAgent,\n    TimeGenerated\n| where isnotempty(HttpUserAgent) and HttpUserAgent !in~ (allUserAgents)\n| summarize\n    EventCount=count(),\n    EventStartTime=min(TimeGenerated),\n    EventEndTime=max(TimeGenerated)\n    by\n    SrcIpAddr,\n    SrcUsername,\n    SrcHostname,\n    DstIpAddr,\n    Url,\n    HttpUserAgent,\n    DstPortNumber\n| extend Name = iif(SrcUsername contains \"@\", tostring(split(SrcUsername,'@',0)[0]),SrcUsername), UPNSuffix = iif(SrcUsername contains \"@\",tostring(split(SrcUsername,'@',1)[0]),\"\")\n",
        "queryFrequency": "PT1H",
        "queryPeriod": "P14D",
        "severity": "Medium",
        "status": "Available",
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "InitialAccess"
        ],
        "tags": [
          {
            "Schema": "WebSession",
            "SchemaVersion": "0.2.6"
          }
        ],
        "techniques": [
          "T1133",
          "T1190"
        ],
        "templateVersion": "1.0.1",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}