Application Gateway WAF - XSS Detection

Severity: high
Time window: 6h
Group by: SQLI_Score, TotalInboundScore, Uri, XSS_Score, action_s, clientIp_s, transactionId_g
Author: shabaz-github
Source: github.com/Azure/Azure-Sentinel

'Identifies a match for XSS attack in the Application gateway WAF logs. The Threshold value in the query can be changed as per your infrastructure's requirement. References: https://owasp.org/www-project-top-ten/2017/A7_2017-Cross-Site_Scripting_(XSS)'

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1189` Drive-by Compromise
Execution	`T1203` Exploitation for Client Execution
Execution	`T0853` Scripting

Rules detecting the same action

These rules filter on the same operation.

Application Gateway WAF - SQLi Detection (Kusto)
Azure WAF matching for Log4j vuln(CVE-2021-44228) (Kusto)
User agent search for log4j exploitation attempt (Kusto)

Rule body

id: d2bc08fa-030a-4eea-931a-762d27c6a042
name: Application Gateway WAF - XSS Detection
description: | 
  'Identifies a match for XSS attack in the Application gateway WAF logs. The Threshold value in the query can be changed as per your infrastructure's requirement.
   References: https://owasp.org/www-project-top-ten/2017/A7_2017-Cross-Site_Scripting_(XSS)'
severity: High 
requiredDataConnectors: 
  - connectorId: WAF 
    dataTypes: 
      - AzureDiagnostics
queryFrequency: 6h 
queryPeriod: 6h 
triggerOperator: gt 
triggerThreshold: 0 
tactics: 
  - InitialAccess
  - Execution
relevantTechniques:
  - T1189
  - T1203
  - T0853
tags:
  - Cross Site Scripting
query:  |  
  let Threshold = 1;  
   AzureDiagnostics
   | where Category == "ApplicationGatewayFirewallLog"
   | where action_s == "Matched"
   | project transactionId_g, hostname_s, requestUri_s, TimeGenerated, clientIp_s, Message, details_message_s, details_data_s
   | join kind = inner(
   AzureDiagnostics
   | where Category == "ApplicationGatewayFirewallLog"
   | where action_s == "Blocked"
   | parse Message with MessageText 'Total Inbound Score: ' TotalInboundScore ' - SQLI=' SQLI_Score ',XSS=' XSS_Score ',RFI=' RFI_Score ',LFI=' LFI_Score ',RCE=' RCE_Score ',PHPI=' PHPI_Score ',HTTP=' HTTP_Score ',SESS=' SESS_Score '): ' Blocked_Reason '; individual paranoia level scores:' Paranoia_Score
   | where Blocked_Reason contains "XSS" and toint(TotalInboundScore) >=15 and toint(XSS_Score) >= 10 and toint(SQLI_Score) <= 5) on transactionId_g
   | extend Uri = strcat(hostname_s,requestUri_s)
   | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), TransactionID = make_set(transactionId_g), Message = make_set(Message), Detail_Message = make_set(details_message_s), Detail_Data = make_set(details_data_s), Total_TransactionId = dcount(transactionId_g) by clientIp_s, Uri, action_s, SQLI_Score, XSS_Score, TotalInboundScore
   | where Total_TransactionId >= Threshold
# The Threshold value above can be changed as per your infrastructure's requirement 
entityMappings:
  - entityType: URL
    fieldMappings:
      - identifier: Url
        columnName: Uri
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: clientIp_s 
version: 1.0.1
kind: Scheduled
metadata:
    source:
        kind: Community
    author:
        name: shabaz-github
    support:
        tier: Community
    categories:
        domains: [ "Security - Threat Protection", "Platform" ]

Stages and Predicates

Parameters

let Threshold = 1;

Stage 1: `source`

AzureDiagnostics

Stage 2: `where`

| where Category == "ApplicationGatewayFirewallLog"

Stage 3: `where`

| where action_s == "Matched"

Stage 4: `project`

| project transactionId_g, hostname_s, requestUri_s, TimeGenerated, clientIp_s, Message, details_message_s, details_data_s

Stage 5: `join`

| join kind = inner(
 AzureDiagnostics
 | where Category == "ApplicationGatewayFirewallLog"
 | where action_s == "Blocked"
 | parse Message with MessageText 'Total Inbound Score: ' TotalInboundScore ' - SQLI=' SQLI_Score ',XSS=' XSS_Score ',RFI=' RFI_Score ',LFI=' LFI_Score ',RCE=' RCE_Score ',PHPI=' PHPI_Score ',HTTP=' HTTP_Score ',SESS=' SESS_Score '): ' Blocked_Reason '; individual paranoia level scores:' Paranoia_Score
 | where Blocked_Reason contains "XSS" and toint(TotalInboundScore) >=15 and toint(XSS_Score) >= 10 and toint(SQLI_Score) <= 5) on transactionId_g

Stage 6: `extend`

| extend Uri = strcat(hostname_s,requestUri_s)

Stage 7: `summarize`

| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), TransactionID = make_set(transactionId_g), Message = make_set(Message), Detail_Message = make_set(details_message_s), Detail_Data = make_set(details_data_s), Total_TransactionId = dcount(transactionId_g) by clientIp_s, Uri, action_s, SQLI_Score, XSS_Score, TotalInboundScore

Stage 8: `where`

| where Total_TransactionId >= Threshold

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Blocked_Reason`	contains	`XSS`	`field:"Blocked_Reason" kind:contains value:"XSS"`
`Category`	eq	`ApplicationGatewayFirewallLog`	`field:"Category" kind:eq value:"ApplicationGatewayFirewallLog"`
`SQLI_Score`	le	`5` transforms: `toint`	`field:"SQLI_Score" kind:le value:"5"`
`TotalInboundScore`	ge	`15` transforms: `toint`	`field:"TotalInboundScore" kind:ge value:"15"`
`Total_TransactionId`	ge	`1`	`field:"Total_TransactionId" kind:ge value:"1"`
`XSS_Score`	ge	`10` transforms: `toint`	`field:"XSS_Score" kind:ge value:"10"`
`action_s`	eq	`Blocked` `Matched`	`field:"action_s" kind:eq`

Output fields

These fields are emitted when the rule matches.

Field	Source
`Detail_Data`	`summarize`
`Detail_Message`	`summarize`
`EndTime`	`summarize`
`Message`	`summarize`
`SQLI_Score`	`summarize`
`StartTime`	`summarize`
`TotalInboundScore`	`summarize`
`Total_TransactionId`	`summarize`
`TransactionID`	`summarize`
`Uri`	`summarize`
`XSS_Score`	`summarize`
`action_s`	`summarize`
`clientIp_s`	`summarize`

Application Gateway WAF - XSS Detection

MITRE ATT&CK coverage

Rules detecting the same action

Rule body

Stages and Predicates

Parameters

Stage 1: source

Stage 2: where

Stage 3: where

Stage 4: project

Stage 5: join

Stage 6: extend

Stage 7: summarize

Stage 8: where