Front Door Premium WAF - XSS Detection

Status: available
Severity: high
Time window: 6h
Group by: action_s, clientIP_s, host_s
Source: github.com/Azure/Azure-Sentinel

'Identifies a match for an XSS attack in the Front Door Premium WAF logs. The threshold value in the query can be changed as per your infrastructure's requirements. 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: b7643904-5081-4920-917e-a559ddc3448f
name: Front Door Premium WAF - XSS Detection
description: | 
  'Identifies a match for an XSS attack in the Front Door Premium WAF logs. The threshold value in the query can be changed as per your infrastructure's requirements.
   References: https://owasp.org/www-project-top-ten/2017/A7_2017-Cross-Site_Scripting_(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 = 1;
    AzureDiagnostics
    | where Category =~ "FrontDoorWebApplicationFirewallLog"
    | where action_s =~ "AnomalyScoring"
    | where details_msg_s has "XSS"
    | parse details_data_s with MessageText "Matched Data:" MatchedData "AND " * "table_name FROM " TableName " " *
    | project trackingReference_s, host_s, requestUri_s, TimeGenerated, clientIP_s, details_matches_s, details_msg_s, details_data_s, TableName, MatchedData
    | join kind = inner(
    AzureDiagnostics
    | where Category =~ "FrontDoorWebApplicationFirewallLog"
    | where action_s =~ "Block") on trackingReference_s
    | summarize URI_s = make_set(requestUri_s,100), Table = make_set(TableName,100), StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), TrackingReference = make_set(trackingReference_s,100), Matched_Data = make_set(MatchedData,100), Detail_Data = make_set(details_data_s,100), Detail_Message = make_set(details_msg_s,100), Total_TrackingReference = dcount(trackingReference_s) by clientIP_s, host_s, action_s
    | where Total_TrackingReference >= Threshold
# The Threshold value above can be changed as per your infrastructure's requirement 
entityMappings:
  - entityType: URL
    fieldMappings:
      - identifier: Url
        columnName: URI_s
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: clientIP_s 
version: 1.0.2
kind: Scheduled

Stages and Predicates

Parameters

let Threshold = 1;

Stage 1: `source`

AzureDiagnostics

Stage 2: `where`

| where Category =~ "FrontDoorWebApplicationFirewallLog"

Stage 3: `where`

| where action_s =~ "AnomalyScoring"

Stage 4: `where`

| where details_msg_s has "XSS"

Stage 5: `parse`

| parse details_data_s with MessageText "Matched Data:" MatchedData "AND " * "table_name FROM " TableName " " *

Stage 6: `project`

| project trackingReference_s, host_s, requestUri_s, TimeGenerated, clientIP_s, details_matches_s, details_msg_s, details_data_s, TableName, MatchedData

Stage 7: `join`

| join kind = inner(
AzureDiagnostics
| where Category =~ "FrontDoorWebApplicationFirewallLog"
| where action_s =~ "Block") on trackingReference_s

Stage 8: `summarize`

| summarize URI_s = make_set(requestUri_s,100), Table = make_set(TableName,100), StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), TrackingReference = make_set(trackingReference_s,100), Matched_Data = make_set(MatchedData,100), Detail_Data = make_set(details_data_s,100), Detail_Message = make_set(details_msg_s,100), Total_TrackingReference = dcount(trackingReference_s) by clientIP_s, host_s, action_s

Threshold: ge 1

Stage 9: `where`

| where Total_TrackingReference >= 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
`Category`	eq	`FrontDoorWebApplicationFirewallLog`
`Total_TrackingReference`	ge	`1` transforms: `cased`
`action_s`	eq	`AnomalyScoring` `Block`
`details_msg_s`	match	`XSS` transforms: `term`

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`
`Matched_Data`	`summarize`
`StartTime`	`summarize`
`Table`	`summarize`
`Total_TrackingReference`	`summarize`
`TrackingReference`	`summarize`
`URI_s`	`summarize`
`action_s`	`summarize`
`clientIP_s`	`summarize`
`host_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)

Front Door Premium 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: `where`

Stage 5: `parse`

Stage 6: `project`

Stage 7: `join`

Stage 8: `summarize`

Stage 9: `where`

Indicators

Output fields

Keyboard shortcuts

Search operators

Front Door Premium 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: where

Stage 5: parse

Stage 6: project

Stage 7: join

Stage 8: summarize

Stage 9: where

Indicators

Output fields

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `where`

Stage 5: `parse`

Stage 6: `project`

Stage 7: `join`

Stage 8: `summarize`

Stage 9: `where`