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
- 70.66% probability · 99th percentile
- Public exploits
- None in Exploit-DB
- 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
EPSS moved from 0.5% on 24 September 2026 to 70.7% on 26 October 2026. The dashed line is the ten per cent mark our analysts treat as “patch before the next change window”.
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, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.