App Gateway WAF - XSS Detection

Status: available
Severity: high
Time window: 6h
Group by: Action, ClientIp, Uri
Source: github.com/Azure/Azure-Sentinel

'Identifies a match for an XSS attack in the App Gateway WAF logs. The threshold value in the query can be changed as per your infrastructure's requirements. References: https://owasp.org/www-community/attacks/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: 1c7ff502-2ad4-4970-9d29-9210c6753138
name: App Gateway WAF - XSS Detection
description: | 
  'Identifies a match for an XSS attack in the App Gateway WAF logs. The threshold value in the query can be changed as per your infrastructure's requirements.
   References: https://owasp.org/www-community/attacks/xss/'
severity: High
status: Available
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 = 3;  
 AGWFirewallLogs
 | where Action == "Matched"
 | where Message has "XSS"
 | project TransactionId, Hostname, RequestUri, TimeGenerated, ClientIp, Message
 | join kind = inner(
 AGWFirewallLogs
 | where Action == "Blocked"
 | extend transactionId_g = tostring(TransactionId)) on TransactionId
 | extend Uri = strcat(Hostname,RequestUri)
 | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), TransactionID = make_set(transactionId_g,100), Message = make_set(Message,100), Total_TransactionId = dcount(transactionId_g) by ClientIp, Uri, Action
 | 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
version: 1.0.2
kind: Scheduled

Stages and Predicates

Parameters

let Threshold = 3;

Stage 1: `source`

AGWFirewallLogs

Stage 2: `where`

| where Action == "Matched"

Stage 3: `where`

| where Message has "XSS"

Stage 4: `project`

| project TransactionId, Hostname, RequestUri, TimeGenerated, ClientIp, Message

Stage 5: `join`

| join kind = inner(
AGWFirewallLogs
| where Action == "Blocked"
| extend transactionId_g = tostring(TransactionId)) on TransactionId

Stage 6: `extend`

| extend Uri = strcat(Hostname,RequestUri)

Stage 7: `summarize`

| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), TransactionID = make_set(transactionId_g,100), Message = make_set(Message,100), Total_TransactionId = dcount(transactionId_g) by ClientIp, Uri, Action

Threshold: ge 3

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
`Action`	eq	`Blocked` transforms: `cased` `Matched` transforms: `cased`
`Message`	match	`XSS` transforms: `term`
`Total_TransactionId`	ge	`3` 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
`Action`	`summarize`
`ClientIp`	`summarize`
`EndTime`	`summarize`
`Message`	`summarize`
`StartTime`	`summarize`
`Total_TransactionId`	`summarize`
`TransactionID`	`summarize`
`Uri`	`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)

App 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

App 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`