Microsoft Exchange Server Cross-Site Scripting Vulnerability
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.
Quick answer
Microsoft should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.
Who is affected
Affected versions
- 2016
- 2019
Fixed versions
- Apply the latest vendor-supported patched version.
How to fix it
CVE-2026-42897 is a Microsoft Exchange Server cross-site scripting and spoofing vulnerability affecting Outlook Web Access rendering conditions. Apply Microsoft guidance immediately: keep Exchange current, enable or verify Exchange Emergency Mitigation Service where applicable, and deploy the Microsoft mitigation or update for this CVE. If OWA is exposed publicly, prioritize mitigation, monitoring, and user-facing phishing controls until every server is remediated.
- Inventory all on-premises Exchange servers, exposed OWA endpoints, cumulative update levels, and emergency mitigation status.
- Apply the Microsoft update or mitigation for CVE-2026-42897 through the supported Exchange servicing path.
- Enable and verify Exchange Emergency Mitigation Service where supported, and confirm it can receive and apply mitigations.
- Use the Exchange Health Checker script or approved operational checks to confirm servers are supported and current enough for mitigations.
- Restrict OWA exposure where possible until mitigation is confirmed on every server.
- Review IIS, OWA, EEMS, mail flow, and security logs for suspicious crafted email activity or script execution indicators.
- Communicate to users and help desk teams that suspicious OWA-rendered messages should be reported and preserved.
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Verify the fix
- Confirm each Exchange server has the relevant Microsoft mitigation or security update applied.
- Verify Exchange Emergency Mitigation Service is enabled and reports healthy status where used.
- Confirm exposed OWA endpoints are protected by the mitigation and unnecessary exposure is reduced.
- Review EEMS, IIS, and Exchange logs for failed or suspicious requests related to the vulnerability.
- Run a Fixnx scan against public Exchange-facing endpoints after remediation.
Related categories
Trusted references
FAQ
What is affected by CVE-2026-42897?
Microsoft should be checked against the vendor advisory and trusted references linked on this page.
What should I fix first?
Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.
How do I confirm the fix worked?
Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.
Why can this risk appear in multiple categories?
A vulnerability can belong to more than one platform or ecosystem. Fixnx keeps one canonical risk page while also listing it in every relevant category.