Application Gateway WAF - XSS Detection

Severity: high
Time window: 6h
Group by: SQLI_Score, TotalInboundScore, Uri, XSS_Score, action_s, clientIp_s
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

Rule body kusto

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

Threshold: ge 1

Stage 8: `where`

| where Total_TransactionId >= Threshold

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`Blocked_Reason`	contains	`XSS`
`Category`	eq	`ApplicationGatewayFirewallLog` transforms: `cased`
`SQLI_Score`	le	`5` transforms: `toint`, `cased`
`TotalInboundScore`	ge	`15` transforms: `toint`, `cased`
`Total_TransactionId`	ge	`1` transforms: `cased`
`XSS_Score`	ge	`10` transforms: `toint`, `cased`
`action_s`	eq	`Blocked` transforms: `cased` `Matched` transforms: `cased`

Output fields

Fields the rule emits when it matches. Chronicle authors list these in the outcome block; they appear on the detection and $risk_score drives alerting. Sentinel / Defender XDR rules build them up through project / summarize / extend stages. Sentinel maps these into alert fields via entityMappings and customDetails; Defender XDR custom detections surface them as alert fields directly.

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`

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

Application Gateway WAF - XSS Detection

MITRE ATT&CK coverage

Rule body kusto

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`

Indicators

Output fields

Keyboard shortcuts

Search operators

Application Gateway WAF - XSS Detection

MITRE ATT&CK coverage

Rule body kusto

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

Indicators

Output fields

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `project`

Stage 5: `join`

Stage 6: `extend`

Stage 7: `summarize`

Stage 8: `where`