A potentially malicious web request was executed against a web server

Back


Id	46ac55ae-47b8-414a-8f94-89ccd1962178
Rulename	A potentially malicious web request was executed against a web server
Description	Detects unobstructed Web Application Firewall (WAF) activity in sessions where the WAF blocked incoming requests by computing the ratio between blocked requests and unobstructed WAF requests in these sessions (BlockvsSuccessRatio metric). A high ratio value for a given client IP and hostname calls for further investigation of the WAF data in that session, due to the significantly high number of blocked requests and a few unobstructed logs which may be malicious but have passed undetected through the WAF. The successCode variable defines what the detection thinks is a successful status code, and should be altered to fit the environment.
Severity	Medium
Tactics	InitialAccess
Techniques	T1190
Required data connectors	WAF
Kind	Scheduled
Query frequency	1d
Query period	1d
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Azure Web Application Firewall (WAF)/Analytic Rules/MaliciousWAFSessions.yaml
Version	1.0.2
Arm template	46ac55ae-47b8-414a-8f94-89ccd1962178.json

KQL

let queryperiod = 1d;
let mode = 'Blocked';
let successCode = dynamic(['200', '101','204', '400','504','304','401','500']);
let sessionBin = 30m;
AzureDiagnostics
| where TimeGenerated > ago(queryperiod)
| where Category == 'ApplicationGatewayFirewallLog' and action_s == mode
| sort by hostname_s asc, clientIp_s asc, TimeGenerated asc
| extend SessionBlockedStarted = row_window_session(TimeGenerated, queryperiod, 10m, ((clientIp_s != prev(clientIp_s)) or (hostname_s != prev(hostname_s))))
| summarize SessionBlockedEnded = max(TimeGenerated), SessionBlockedCount = count() by hostname_s, clientIp_s, SessionBlockedStarted
| extend TimeKey = range(bin(SessionBlockedStarted, sessionBin), bin(SessionBlockedEnded, sessionBin), sessionBin)
| mv-expand TimeKey to typeof(datetime)
| join kind = inner(
    AzureDiagnostics
    | where TimeGenerated > ago(queryperiod)
    | where Category == 'ApplicationGatewayAccessLog' and (isempty(httpStatus_d) or httpStatus_d in (successCode))
    | extend TimeKey = bin(TimeGenerated, sessionBin)
) on TimeKey, $left.hostname_s == $right.host_s, $left.clientIp_s == $right.clientIP_s
| where TimeGenerated between (SessionBlockedStarted..SessionBlockedEnded)
| extend
    originalRequestUriWithArgs_s = column_ifexists("originalRequestUriWithArgs_s", ""),
    serverStatus_s = column_ifexists("serverStatus_s", "")
| summarize
    SuccessfulAccessCount = count(),
    UserAgents = make_set(userAgent_s, 250),
    RequestURIs = make_set(requestUri_s, 250),
    OriginalRequestURIs = make_set(originalRequestUriWithArgs_s, 250),
    SuccessCodes = make_set(httpStatus_d, 250),
    SuccessCodes_BackendServer = make_set(serverStatus_s, 250),
    take_any(SessionBlockedEnded, SessionBlockedCount)
    by hostname_s, clientIp_s, SessionBlockedStarted
| where SessionBlockedCount > SuccessfulAccessCount
| extend timestamp = SessionBlockedStarted, IPCustomEntity = clientIp_s
| extend BlockvsSuccessRatio = SessionBlockedCount/toreal(SuccessfulAccessCount)
| sort by BlockvsSuccessRatio desc, timestamp asc
| project-reorder SessionBlockedStarted, SessionBlockedEnded, hostname_s, clientIp_s, SessionBlockedCount, SuccessfulAccessCount, BlockvsSuccessRatio, SuccessCodes, RequestURIs, OriginalRequestURIs, UserAgents

YAML

name: A potentially malicious web request was executed against a web server
query: |
  let queryperiod = 1d;
  let mode = 'Blocked';
  let successCode = dynamic(['200', '101','204', '400','504','304','401','500']);
  let sessionBin = 30m;
  AzureDiagnostics
  | where TimeGenerated > ago(queryperiod)
  | where Category == 'ApplicationGatewayFirewallLog' and action_s == mode
  | sort by hostname_s asc, clientIp_s asc, TimeGenerated asc
  | extend SessionBlockedStarted = row_window_session(TimeGenerated, queryperiod, 10m, ((clientIp_s != prev(clientIp_s)) or (hostname_s != prev(hostname_s))))
  | summarize SessionBlockedEnded = max(TimeGenerated), SessionBlockedCount = count() by hostname_s, clientIp_s, SessionBlockedStarted
  | extend TimeKey = range(bin(SessionBlockedStarted, sessionBin), bin(SessionBlockedEnded, sessionBin), sessionBin)
  | mv-expand TimeKey to typeof(datetime)
  | join kind = inner(
      AzureDiagnostics
      | where TimeGenerated > ago(queryperiod)
      | where Category == 'ApplicationGatewayAccessLog' and (isempty(httpStatus_d) or httpStatus_d in (successCode))
      | extend TimeKey = bin(TimeGenerated, sessionBin)
  ) on TimeKey, $left.hostname_s == $right.host_s, $left.clientIp_s == $right.clientIP_s
  | where TimeGenerated between (SessionBlockedStarted..SessionBlockedEnded)
  | extend
      originalRequestUriWithArgs_s = column_ifexists("originalRequestUriWithArgs_s", ""),
      serverStatus_s = column_ifexists("serverStatus_s", "")
  | summarize
      SuccessfulAccessCount = count(),
      UserAgents = make_set(userAgent_s, 250),
      RequestURIs = make_set(requestUri_s, 250),
      OriginalRequestURIs = make_set(originalRequestUriWithArgs_s, 250),
      SuccessCodes = make_set(httpStatus_d, 250),
      SuccessCodes_BackendServer = make_set(serverStatus_s, 250),
      take_any(SessionBlockedEnded, SessionBlockedCount)
      by hostname_s, clientIp_s, SessionBlockedStarted
  | where SessionBlockedCount > SuccessfulAccessCount
  | extend timestamp = SessionBlockedStarted, IPCustomEntity = clientIp_s
  | extend BlockvsSuccessRatio = SessionBlockedCount/toreal(SuccessfulAccessCount)
  | sort by BlockvsSuccessRatio desc, timestamp asc
  | project-reorder SessionBlockedStarted, SessionBlockedEnded, hostname_s, clientIp_s, SessionBlockedCount, SuccessfulAccessCount, BlockvsSuccessRatio, SuccessCodes, RequestURIs, OriginalRequestURIs, UserAgents  
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Azure Web Application Firewall (WAF)/Analytic Rules/MaliciousWAFSessions.yaml
queryFrequency: 1d
triggerThreshold: 0
requiredDataConnectors:
- dataTypes:
  - AzureDiagnostics
  connectorId: WAF
version: 1.0.2
status: Available
queryPeriod: 1d
id: 46ac55ae-47b8-414a-8f94-89ccd1962178
triggerOperator: gt
entityMappings:
- fieldMappings:
  - identifier: Address
    columnName: IPCustomEntity
  entityType: IP
relevantTechniques:
- T1190
severity: Medium
description: |
  'Detects unobstructed Web Application Firewall (WAF) activity in sessions where the WAF blocked incoming requests by computing the 
  ratio between blocked requests and unobstructed WAF requests in these sessions (BlockvsSuccessRatio metric). A high ratio value for 
  a given client IP and hostname calls for further investigation of the WAF data in that session, due to the significantly high number 
  of blocked requests and a few unobstructed logs which may be malicious but have passed undetected through the WAF. The successCode 
  variable defines what the detection thinks is a successful status code, and should be altered to fit the environment.'  
kind: Scheduled
tactics:
- InitialAccess

ARM

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "workspace": {
      "type": "String"
    }
  },
  "resources": [
    {
      "id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/46ac55ae-47b8-414a-8f94-89ccd1962178')]",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/46ac55ae-47b8-414a-8f94-89ccd1962178')]",
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules",
      "kind": "Scheduled",
      "apiVersion": "2022-11-01",
      "properties": {
        "displayName": "A potentially malicious web request was executed against a web server",
        "description": "'Detects unobstructed Web Application Firewall (WAF) activity in sessions where the WAF blocked incoming requests by computing the \nratio between blocked requests and unobstructed WAF requests in these sessions (BlockvsSuccessRatio metric). A high ratio value for \na given client IP and hostname calls for further investigation of the WAF data in that session, due to the significantly high number \nof blocked requests and a few unobstructed logs which may be malicious but have passed undetected through the WAF. The successCode \nvariable defines what the detection thinks is a successful status code, and should be altered to fit the environment.'\n",
        "severity": "Medium",
        "enabled": true,
        "query": "let queryperiod = 1d;\nlet mode = 'Blocked';\nlet successCode = dynamic(['200', '101','204', '400','504','304','401','500']);\nlet sessionBin = 30m;\nAzureDiagnostics\n| where TimeGenerated > ago(queryperiod)\n| where Category == 'ApplicationGatewayFirewallLog' and action_s == mode\n| sort by hostname_s asc, clientIp_s asc, TimeGenerated asc\n| extend SessionBlockedStarted = row_window_session(TimeGenerated, queryperiod, 10m, ((clientIp_s != prev(clientIp_s)) or (hostname_s != prev(hostname_s))))\n| summarize SessionBlockedEnded = max(TimeGenerated), SessionBlockedCount = count() by hostname_s, clientIp_s, SessionBlockedStarted\n| extend TimeKey = range(bin(SessionBlockedStarted, sessionBin), bin(SessionBlockedEnded, sessionBin), sessionBin)\n| mv-expand TimeKey to typeof(datetime)\n| join kind = inner(\n    AzureDiagnostics\n    | where TimeGenerated > ago(queryperiod)\n    | where Category == 'ApplicationGatewayAccessLog' and (isempty(httpStatus_d) or httpStatus_d in (successCode))\n    | extend TimeKey = bin(TimeGenerated, sessionBin)\n) on TimeKey, $left.hostname_s == $right.host_s, $left.clientIp_s == $right.clientIP_s\n| where TimeGenerated between (SessionBlockedStarted..SessionBlockedEnded)\n| extend\n    originalRequestUriWithArgs_s = column_ifexists(\"originalRequestUriWithArgs_s\", \"\"),\n    serverStatus_s = column_ifexists(\"serverStatus_s\", \"\")\n| summarize\n    SuccessfulAccessCount = count(),\n    UserAgents = make_set(userAgent_s, 250),\n    RequestURIs = make_set(requestUri_s, 250),\n    OriginalRequestURIs = make_set(originalRequestUriWithArgs_s, 250),\n    SuccessCodes = make_set(httpStatus_d, 250),\n    SuccessCodes_BackendServer = make_set(serverStatus_s, 250),\n    take_any(SessionBlockedEnded, SessionBlockedCount)\n    by hostname_s, clientIp_s, SessionBlockedStarted\n| where SessionBlockedCount > SuccessfulAccessCount\n| extend timestamp = SessionBlockedStarted, IPCustomEntity = clientIp_s\n| extend BlockvsSuccessRatio = SessionBlockedCount/toreal(SuccessfulAccessCount)\n| sort by BlockvsSuccessRatio desc, timestamp asc\n| project-reorder SessionBlockedStarted, SessionBlockedEnded, hostname_s, clientIp_s, SessionBlockedCount, SuccessfulAccessCount, BlockvsSuccessRatio, SuccessCodes, RequestURIs, OriginalRequestURIs, UserAgents\n",
        "queryFrequency": "P1D",
        "queryPeriod": "P1D",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0,
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "InitialAccess"
        ],
        "techniques": [
          "T1190"
        ],
        "alertRuleTemplateName": "46ac55ae-47b8-414a-8f94-89ccd1962178",
        "customDetails": null,
        "entityMappings": [
          {
            "fieldMappings": [
              {
                "identifier": "Address",
                "columnName": "IPCustomEntity"
              }
            ],
            "entityType": "IP"
          }
        ],
        "status": "Available",
        "templateVersion": "1.0.2",
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Azure Web Application Firewall (WAF)/Analytic Rules/MaliciousWAFSessions.yaml"
      }
    }
  ]
}