Detect web requests to potentially harmful files ASIM Web Session

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Id	c6608467-3678-45fe-b038-b590ce6d00fb
Rulename	Detect web requests to potentially harmful files (ASIM Web Session)
Description	This rule detects web requests made to URLs containing file types such as .ps1, .bat, .vbs,.scr etc. which have the potential to be harmful if downloaded. This rule uses the Advanced Security Information Model (ASIM) and supports any web session source that complies with ASIM.
Severity	Medium
Tactics	InitialAccess Persistence Execution
Techniques	T1133 T1203 T1566
Kind	Scheduled
Query frequency	5m
Query period	5m
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Web Session Essentials/Analytic Rules/RequestToPotentiallyHarmfulFileTypes.yaml
Version	1.0.0
Arm template	c6608467-3678-45fe-b038-b590ce6d00fb.json

KQL

let lookback = 5m;
let RiskyFileExtensions = materialize(externaldata(Extensions: string)
    [@"https://raw.githubusercontent.com/Azure/Azure-Sentinel/master/Sample%20Data/Feeds/RiskyFileExtensionsInUrl.csv"]
    with(format="csv", ignoreFirstRecord=True));
let CustomRiskyFileExtensions = (_ASIM_GetWatchlistRaw("Web_RiskyFileExtensions") // Create new Watchlist and add your custom indicators(Optional)
    | extend
        Extensions = tostring(WatchlistItem["Extensions"])
    | project Extensions
    | where isnotempty(Extensions));
let CombinedRiskyFileExtensions = union RiskyFileExtensions, CustomRiskyFileExtensions;
let knownRiskyFileExtensions=toscalar(CombinedRiskyFileExtensions
    | where isnotempty(Extensions)
    | summarize make_set(Extensions, 1000));
let Whitelisted_Domains = materialize(externaldata(WhiteListedDomains: string)
    [@"https://raw.githubusercontent.com/Azure/Azure-Sentinel/master/Sample%20Data/Feeds/WhiteListedDomainsForWebSessionUseCases.csv"]
    with(format="csv", ignoreFirstRecord=True));
let CustomWhiteListedDomains = (_ASIM_GetWatchlistRaw("Web_WhiteListedDomains") // Create new Watchlist and add your white listed domains(Optional)
    | extend
        WhiteListedDomains = tostring(WatchlistItem["WhiteListedDomains"])
    | project WhiteListedDomains
    | where isnotempty(WhiteListedDomains));
let CombinedWhitelisted_Domains = union Whitelisted_Domains, CustomWhiteListedDomains;
let knownWhitelisted_Domains=toscalar(CombinedWhitelisted_Domains
    | where isnotempty(WhiteListedDomains)
    | summarize make_set(WhiteListedDomains, 1000));
_Im_WebSession (starttime=ago(lookback), url_has_any=knownRiskyFileExtensions, eventresult='Success')
| project
    Url,
    SrcIpAddr,
    TimeGenerated,
    SrcUsername,
    SrcHostname,
    DstIpAddr,
    DstPortNumber
| extend requestedFileName=tostring(split(tostring(parse_url(Url)["Path"]), '/')[-1])
| extend requestedFileExt=extract(@'(\.\w+)$', 1, requestedFileName, typeof(string))
| where requestedFileExt in~ (knownRiskyFileExtensions)
| summarize
    EventCount=count(),
    EventStartTime=min(TimeGenerated),
    EventEndTime=max(TimeGenerated)
    by
    SrcUsername,
    SrcIpAddr,
    SrcHostname,
    DstIpAddr,
    DstPortNumber,
    Url,
    requestedFileName
| extend FQDN = split(parse_url(Url)["Host"], '.')
| extend Domain = iif(array_length(FQDN) > 1, strcat(FQDN[-2], '.', FQDN[-1]), FQDN)
| where Domain !in~ (knownWhitelisted_Domains)
| project-away FQDN
| extend Name = iif(SrcUsername contains "@", tostring(split(SrcUsername,'@',0)[0]),SrcUsername), UPNSuffix = iif(SrcUsername contains "@",tostring(split(SrcUsername,'@',1)[0]),"")

YAML

status: Available
queryFrequency: 5m
description: |
    'This rule detects web requests made to URLs containing file types such as .ps1, .bat, .vbs,.scr etc. which have the potential to be harmful if downloaded. This rule uses the [Advanced Security Information Model (ASIM)](https://aka.ms/AboutASIM) and supports any web session source that complies with ASIM.'
customDetails:
  DstIpAddr: DstIpAddr
  EventStartTime: EventStartTime
  EventCount: EventCount
  EventEndTime: EventEndTime
severity: Medium
version: 1.0.0
relevantTechniques:
- T1133
- T1203
- T1566
kind: Scheduled
name: Detect web requests to potentially harmful files (ASIM Web Session)
triggerThreshold: 0
eventGroupingSettings:
  aggregationKind: AlertPerResult
query: |
  let lookback = 5m;
  let RiskyFileExtensions = materialize(externaldata(Extensions: string)
      [@"https://raw.githubusercontent.com/Azure/Azure-Sentinel/master/Sample%20Data/Feeds/RiskyFileExtensionsInUrl.csv"]
      with(format="csv", ignoreFirstRecord=True));
  let CustomRiskyFileExtensions = (_ASIM_GetWatchlistRaw("Web_RiskyFileExtensions") // Create new Watchlist and add your custom indicators(Optional)
      | extend
          Extensions = tostring(WatchlistItem["Extensions"])
      | project Extensions
      | where isnotempty(Extensions));
  let CombinedRiskyFileExtensions = union RiskyFileExtensions, CustomRiskyFileExtensions;
  let knownRiskyFileExtensions=toscalar(CombinedRiskyFileExtensions
      | where isnotempty(Extensions)
      | summarize make_set(Extensions, 1000));
  let Whitelisted_Domains = materialize(externaldata(WhiteListedDomains: string)
      [@"https://raw.githubusercontent.com/Azure/Azure-Sentinel/master/Sample%20Data/Feeds/WhiteListedDomainsForWebSessionUseCases.csv"]
      with(format="csv", ignoreFirstRecord=True));
  let CustomWhiteListedDomains = (_ASIM_GetWatchlistRaw("Web_WhiteListedDomains") // Create new Watchlist and add your white listed domains(Optional)
      | extend
          WhiteListedDomains = tostring(WatchlistItem["WhiteListedDomains"])
      | project WhiteListedDomains
      | where isnotempty(WhiteListedDomains));
  let CombinedWhitelisted_Domains = union Whitelisted_Domains, CustomWhiteListedDomains;
  let knownWhitelisted_Domains=toscalar(CombinedWhitelisted_Domains
      | where isnotempty(WhiteListedDomains)
      | summarize make_set(WhiteListedDomains, 1000));
  _Im_WebSession (starttime=ago(lookback), url_has_any=knownRiskyFileExtensions, eventresult='Success')
  | project
      Url,
      SrcIpAddr,
      TimeGenerated,
      SrcUsername,
      SrcHostname,
      DstIpAddr,
      DstPortNumber
  | extend requestedFileName=tostring(split(tostring(parse_url(Url)["Path"]), '/')[-1])
  | extend requestedFileExt=extract(@'(\.\w+)$', 1, requestedFileName, typeof(string))
  | where requestedFileExt in~ (knownRiskyFileExtensions)
  | summarize
      EventCount=count(),
      EventStartTime=min(TimeGenerated),
      EventEndTime=max(TimeGenerated)
      by
      SrcUsername,
      SrcIpAddr,
      SrcHostname,
      DstIpAddr,
      DstPortNumber,
      Url,
      requestedFileName
  | extend FQDN = split(parse_url(Url)["Host"], '.')
  | extend Domain = iif(array_length(FQDN) > 1, strcat(FQDN[-2], '.', FQDN[-1]), FQDN)
  | where Domain !in~ (knownWhitelisted_Domains)
  | project-away FQDN
  | extend Name = iif(SrcUsername contains "@", tostring(split(SrcUsername,'@',0)[0]),SrcUsername), UPNSuffix = iif(SrcUsername contains "@",tostring(split(SrcUsername,'@',1)[0]),"")  
alertDetailsOverride:
  alertDisplayNameFormat: User '{{SrcUsername}}' with IP address '{{SrcIpAddr}}' accessed a potentially harmful URL
  alertDescriptionFormat: User accessed URL - '{{Url}}' that contains a file - '{{requestedFileName}}' with risky extension. Downloading this file could pose a potential risk
triggerOperator: gt
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Web Session Essentials/Analytic Rules/RequestToPotentiallyHarmfulFileTypes.yaml
requiredDataConnectors: []
tactics:
- InitialAccess
- Persistence
- Execution
tags:
- SchemaVersion: 0.2.6
  Schema: WebSession
id: c6608467-3678-45fe-b038-b590ce6d00fb
queryPeriod: 5m
entityMappings:
- fieldMappings:
  - columnName: SrcIpAddr
    identifier: Address
  entityType: IP
- fieldMappings:
  - columnName: Url
    identifier: Url
  entityType: URL
- fieldMappings:
  - columnName: requestedFileName
    identifier: Name
  entityType: File
- fieldMappings:
  - columnName: SrcHostname
    identifier: HostName
  entityType: Host
- fieldMappings:
  - columnName: Name
    identifier: Name
  - columnName: UPNSuffix
    identifier: UPNSuffix
  entityType: Account

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/c6608467-3678-45fe-b038-b590ce6d00fb')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/c6608467-3678-45fe-b038-b590ce6d00fb')]",
      "properties": {
        "alertDetailsOverride": {
          "alertDescriptionFormat": "User accessed URL - '{{Url}}' that contains a file - '{{requestedFileName}}' with risky extension. Downloading this file could pose a potential risk",
          "alertDisplayNameFormat": "User '{{SrcUsername}}' with IP address '{{SrcIpAddr}}' accessed a potentially harmful URL"
        },
        "alertRuleTemplateName": "c6608467-3678-45fe-b038-b590ce6d00fb",
        "customDetails": {
          "DstIpAddr": "DstIpAddr",
          "EventCount": "EventCount",
          "EventEndTime": "EventEndTime",
          "EventStartTime": "EventStartTime"
        },
        "description": "'This rule detects web requests made to URLs containing file types such as .ps1, .bat, .vbs,.scr etc. which have the potential to be harmful if downloaded. This rule uses the [Advanced Security Information Model (ASIM)](https://aka.ms/AboutASIM) and supports any web session source that complies with ASIM.'\n",
        "displayName": "Detect web requests to potentially harmful files (ASIM Web Session)",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "SrcIpAddr",
                "identifier": "Address"
              }
            ]
          },
          {
            "entityType": "URL",
            "fieldMappings": [
              {
                "columnName": "Url",
                "identifier": "Url"
              }
            ]
          },
          {
            "entityType": "File",
            "fieldMappings": [
              {
                "columnName": "requestedFileName",
                "identifier": "Name"
              }
            ]
          },
          {
            "entityType": "Host",
            "fieldMappings": [
              {
                "columnName": "SrcHostname",
                "identifier": "HostName"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "Name",
                "identifier": "Name"
              },
              {
                "columnName": "UPNSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          }
        ],
        "eventGroupingSettings": {
          "aggregationKind": "AlertPerResult"
        },
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Web Session Essentials/Analytic Rules/RequestToPotentiallyHarmfulFileTypes.yaml",
        "query": "let lookback = 5m;\nlet RiskyFileExtensions = materialize(externaldata(Extensions: string)\n    [@\"https://raw.githubusercontent.com/Azure/Azure-Sentinel/master/Sample%20Data/Feeds/RiskyFileExtensionsInUrl.csv\"]\n    with(format=\"csv\", ignoreFirstRecord=True));\nlet CustomRiskyFileExtensions = (_ASIM_GetWatchlistRaw(\"Web_RiskyFileExtensions\") // Create new Watchlist and add your custom indicators(Optional)\n    | extend\n        Extensions = tostring(WatchlistItem[\"Extensions\"])\n    | project Extensions\n    | where isnotempty(Extensions));\nlet CombinedRiskyFileExtensions = union RiskyFileExtensions, CustomRiskyFileExtensions;\nlet knownRiskyFileExtensions=toscalar(CombinedRiskyFileExtensions\n    | where isnotempty(Extensions)\n    | summarize make_set(Extensions, 1000));\nlet Whitelisted_Domains = materialize(externaldata(WhiteListedDomains: string)\n    [@\"https://raw.githubusercontent.com/Azure/Azure-Sentinel/master/Sample%20Data/Feeds/WhiteListedDomainsForWebSessionUseCases.csv\"]\n    with(format=\"csv\", ignoreFirstRecord=True));\nlet CustomWhiteListedDomains = (_ASIM_GetWatchlistRaw(\"Web_WhiteListedDomains\") // Create new Watchlist and add your white listed domains(Optional)\n    | extend\n        WhiteListedDomains = tostring(WatchlistItem[\"WhiteListedDomains\"])\n    | project WhiteListedDomains\n    | where isnotempty(WhiteListedDomains));\nlet CombinedWhitelisted_Domains = union Whitelisted_Domains, CustomWhiteListedDomains;\nlet knownWhitelisted_Domains=toscalar(CombinedWhitelisted_Domains\n    | where isnotempty(WhiteListedDomains)\n    | summarize make_set(WhiteListedDomains, 1000));\n_Im_WebSession (starttime=ago(lookback), url_has_any=knownRiskyFileExtensions, eventresult='Success')\n| project\n    Url,\n    SrcIpAddr,\n    TimeGenerated,\n    SrcUsername,\n    SrcHostname,\n    DstIpAddr,\n    DstPortNumber\n| extend requestedFileName=tostring(split(tostring(parse_url(Url)[\"Path\"]), '/')[-1])\n| extend requestedFileExt=extract(@'(\\.\\w+)$', 1, requestedFileName, typeof(string))\n| where requestedFileExt in~ (knownRiskyFileExtensions)\n| summarize\n    EventCount=count(),\n    EventStartTime=min(TimeGenerated),\n    EventEndTime=max(TimeGenerated)\n    by\n    SrcUsername,\n    SrcIpAddr,\n    SrcHostname,\n    DstIpAddr,\n    DstPortNumber,\n    Url,\n    requestedFileName\n| extend FQDN = split(parse_url(Url)[\"Host\"], '.')\n| extend Domain = iif(array_length(FQDN) > 1, strcat(FQDN[-2], '.', FQDN[-1]), FQDN)\n| where Domain !in~ (knownWhitelisted_Domains)\n| project-away FQDN\n| extend Name = iif(SrcUsername contains \"@\", tostring(split(SrcUsername,'@',0)[0]),SrcUsername), UPNSuffix = iif(SrcUsername contains \"@\",tostring(split(SrcUsername,'@',1)[0]),\"\")\n",
        "queryFrequency": "PT5M",
        "queryPeriod": "PT5M",
        "severity": "Medium",
        "status": "Available",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "Execution",
          "InitialAccess",
          "Persistence"
        ],
        "tags": [
          {
            "Schema": "WebSession",
            "SchemaVersion": "0.2.6"
          }
        ],
        "techniques": [
          "T1133",
          "T1203",
          "T1566"
        ],
        "templateVersion": "1.0.0",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}