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

severity: Medium
relevantTechniques:
- T1133
- T1203
- T1566
customDetails:
  EventStartTime: EventStartTime
  DstIpAddr: DstIpAddr
  EventCount: EventCount
  EventEndTime: EventEndTime
queryFrequency: 5m
kind: Scheduled
version: 1.0.0
name: Detect web requests to potentially harmful files (ASIM Web Session)
triggerOperator: gt
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.'
queryPeriod: 5m
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
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
tactics:
- InitialAccess
- Persistence
- Execution
status: Available
triggerThreshold: 0
tags:
- Schema: WebSession
  SchemaVersion: 0.2.6
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Web Session Essentials/Analytic Rules/RequestToPotentiallyHarmfulFileTypes.yaml
eventGroupingSettings:
  aggregationKind: AlertPerResult
id: c6608467-3678-45fe-b038-b590ce6d00fb
requiredDataConnectors: []

ARM

{
  "$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/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",
        "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"
    }
  ]
}