Detection rules › Kusto

Cloudflare - XSS probing pattern in request

Status
available
Severity
medium
Time window
1h
Source
github.com/Azure/Azure-Sentinel

'Detects XSS probing patterns.'

MITRE ATT&CK coverage

Rule body kusto

id: 4d9d00b9-31a6-49e4-88c1-9e68277053ac
name: Cloudflare - XSS probing pattern in request
description: |
  'Detects XSS probing patterns.'
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: CloudflareDataConnector
    dataTypes:
      - Cloudflare
queryFrequency: 1h
queryPeriod: 1h
triggerOperator: gt
triggerThreshold: 0
tactics:
  - InitialAccess
relevantTechniques:
  - T1190
  - T1133
query: |
  let s_threshold = 3;
  Cloudflare
  | where HttpRequestMethod in~ ('POST', 'PUT')
  | extend susp_ch = countof(ClientRequestURI, '%00')
  | where ClientRequestURI matches regex @'(alert\()|(alert\%28)|(String\.fromCharCode\()|(expression\(alert)' or susp_ch > s_threshold 
  | extend CompleteUrl = strcat(HttpRequestHeaderHost,ClientRequestPath)
entityMappings:
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SrcIpAddr
  - entityType: URL
    fieldMappings:
      - identifier: Url
        columnName: CompleteUrl
version: 1.0.1
kind: Scheduled

Stages and Predicates

Parameters

let s_threshold = 3;

Stage 1: source

Cloudflare

Stage 2: where

| where HttpRequestMethod in~ ('POST', 'PUT')

Stage 3: extend

| extend susp_ch = countof(ClientRequestURI, '%00')

Stage 4: where

| where ClientRequestURI matches regex @'(alert\()|(alert\%28)|(String\.fromCharCode\()|(expression\(alert)' or susp_ch > s_threshold

Stage 5: extend

| extend CompleteUrl = strcat(HttpRequestHeaderHost,ClientRequestPath)

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.

FieldKindValues
ClientRequestURIregex_match
    • (alert()
    • (alert\%28)
    • (String.fromCharCode()
    • (expression(alert)
HttpRequestMethodin
  • POST
  • PUT
susp_chgt
  • 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.

FieldSource
susp_chextend
CompleteUrlextend