CVE-2026-42897
Microsoft Exchange Server Cross-Site Scripting Vulnerability
Does this matter?
Known to be exploited in the wild (CISA KEV, CISA remediation deadline 29 May 2026). Treat as an emergency change: patch or isolate now, then hunt for prior compromise.
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.
- CVSS 3.1
- 6.1 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- EPSS
- 71.20% probability · 99th percentile
- CISA KEV
- Listed 15 May 2026 · due 29 May 2026
- Weakness
- CWE-79
- Affected
- microsoft/exchange server · microsoft/exchange server subscription edition
- Source
- secure@microsoft.com
CISA notes
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. 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
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-42897Mitigation, Vendor Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-42897US Government Resource
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.