CVE-2026-42897: Microsoft Exchange Server Cross-Site Scripting Vulnerability

CISA Known Exploited Vulnerability (KEV)

Description

Microsoft Exchange Server contains a cross-site scripting vulnerability during web page generation in Outlook Web Access and when certain interaction conditions are met, arbitrary JavaScript can be executed in the browser context.

Required action (CISA)

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Notes

https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2026-42897 ; https://learn.microsoft.com/en-us/exchange/plan-and-deploy/post-installation-tasks/security-best-practices/exchange-emergency-mitigation-service ; https://nvd.nist.gov/vuln/detail/CVE-2026-42897

Weakness behind it

CISA records this vulnerability as an instance of CWE-79. From there the chain continues into CAPEC attack patterns and ATT&CK techniques, all inside this corpus.

References

• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42897
• KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog