CVE-2026-42897

What the flaw is

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.

Description as published by CISA. We have not independently reproduced it.

What CISA requires

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

This deadline is binding on US federal civilian agencies under BOD 22-01. It is not a legal deadline for anyone else, but it is a useful urgency signal — CISA sets it by how actively the flaw is being used, not by CVSS.

Public exploit code

We hold no public exploit references for this CVE. That means our dataset has none — it is not evidence that no exploit exists. CISA has confirmed this vulnerability is being exploited in the wild regardless.

Vendor advisories

• msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2026-42897
• learn.microsoft.com/en-us/exchange/plan-and-deploy/post-installation-tasks/sec
• nvd.nist.gov/vuln/detail/CVE-2026-42897

Primary sources

• NVD entry — CVSS score, CPE list and references
• CISA KEV catalog — the source for this page
• CVE Record at cve.org