Detect Microsoft Exchange Server Cross-Site Scripting (XSS) Exploitation in IBM QRadar
Detects exploitation attempts targeting CVE-2026-42897, a Cross-Site Scripting (XSS) vulnerability in Microsoft Exchange Server. This KEV-listed vulnerability allows attackers to inject malicious scripts into Exchange web interfaces, potentially leading to session hijacking, credential theft, or further lateral movement within the environment. Detection focuses on anomalous HTTP requests to Exchange OWA/ECP endpoints containing XSS payloads, unexpected script execution from Exchange processes, and suspicious web request patterns indicative of active exploitation.
MITRE ATT&CK
QRadar Detection Query
SELECT
DATEFORMAT(starttime, 'YYYY-MM-dd HH:mm:ss') AS event_time,
sourceip,
username,
URL,
'XSS Payload Detected' AS detection_reason,
CASE
WHEN URL LIKE '%document.cookie%' THEN 'Critical'
WHEN URL LIKE '%<script%' THEN 'High'
ELSE 'Medium'
END AS severity
FROM events
WHERE
LOGSOURCETYPENAME(devicetype) ILIKE '%IIS%'
AND (
URL LIKE '%/owa/%'
OR URL LIKE '%/ecp/%'
OR URL LIKE '%/ews/%'
OR URL LIKE '%/autodiscover/%'
)
AND (
URL ILIKE '%<script%'
OR URL ILIKE '%javascript:%'
OR URL ILIKE '%onerror=%'
OR URL ILIKE '%onload=%'
OR URL ILIKE '%eval(%'
OR URL ILIKE '%document.cookie%'
OR URL ILIKE '%fromCharCode%'
OR URL ILIKE '%%3Cscript%'
)
AND STARTTIME > NOW() - 86400000
ORDER BY starttime DESC
LIMIT 500QRadar AQL query detecting XSS payload patterns in HTTP requests to Microsoft Exchange OWA, ECP, EWS, and Autodiscover endpoints via IIS log sources.
Data Sources
Required Tables
False Positives & Tuning
- Vulnerability scanners performing authorized assessments of Exchange infrastructure
- Red team engagements that deliberately inject XSS test strings
- Application URL parameters containing encoded characters resembling XSS syntax
- WAF validation tools that replay known attack patterns for rule testing
Other platforms for CVE-2026-42897
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Basic Reflected XSS Probe Against Exchange OWA
Expected signal: IIS access log entry with HTTP GET or POST to /owa/auth/logon.aspx containing the URL-encoded XSS payload in cs-uri-query field; source IP of the test machine visible in c-ip field.
- Test 2Cookie-Stealing XSS Payload Delivery to Exchange ECP
Expected signal: IIS access log shows request to /ecp/ with onerror= and document.cookie in the query string, sc-status may be 200 or 400; network log may show outbound HTTP to attacker server if payload executes in a browser context.
- Test 3Encoded XSS Bypass Attempt Against Exchange Autodiscover
Expected signal: IIS access logs show multiple GET requests to /autodiscover/autodiscover.xml with encoded XSS strings in cs-uri-query; Windows PowerShell event log (Event ID 4104) may capture the script block execution.
Unlock Pro Content
Get the full detection package for CVE-2026-42897 including response playbook, investigation guide, and atomic red team tests.