CVE-2026-42897 — Exchange Server
HIGHCVE-2026-42897 is a high-severity (CVSS 8.1) Cross-site Scripting (XSS) vulnerability in microsoft exchange server. It is in CISA's Known Exploited Vulnerabilities catalog (added 2026-05-15) — treat it as actively exploited and patch now. A fix is available — see the affected versions and patch details below.
Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.
Exploitation Status
Actively exploited in the wild
- Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2026-05-15. Federal agencies were required to remediate by 2026-05-29.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2026-42897.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-42897 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 395,249 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Description
Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.
Affected Products
exchange servermicrosoftexchange server subscription editionmicrosoftResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Vendor / applianceDetect
Inventory every microsoft exchange server deployment and check each version against the affected-products list above.
Fix
Apply the microsoft exchange server security patch or hotfix for CVE-2026-42897 on the affected version, following the vendor advisory for your exact build.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.
Frequently Asked Questions
Is CVE-2026-42897 being exploited in your environment?
Detect and block the exploit chain at execution, on systems you cannot patch yet.