Exploited vulnerability · CISA KEV

Is CVE-2026-42897 exploited? Yes: in CISA KEV since 15 May 2026

Gociux · Microsoft · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2026-42897, Microsoft Exchange Server Cross-Site Scripting Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 15 May 2026, 1 days after it was published. It affects Microsoft. If you run it, CISA's required action is: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

What it 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.

What to do

1. Check whether you run it. Look for Microsoft in your asset inventory, including appliances and cloud images. Stack check lists every exploited Microsoft CVE at once.
2. Apply the fix. Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
3. If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 14 May 2026.
4. Get told next time. Email alerts when CISA adds a CVE for Microsoft.

References

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

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in May 2026 · Microsoft scorecard · act-now radar.