How severe is CVE-2026-42897?

CVE-2026-42897 has a CVSS 3.1 base score of 8.1 (HIGH). EPSS estimates a 0.5% probability of exploitation in the next 30 days. It is listed in the CISA Known Exploited Vulnerabilities catalog.

CVE-2026-42897: Microsoft Exchange Server Spoofing Vulnerability

CISA Known Exploited Vulnerabilities

Microsoft Exchange Server Cross-Site Scripting Vulnerability is confirmed as actively exploited and is listed in the CISA KEV catalog.

Added to KEV

2026-05-15

Remediation due

2026-05-29

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

CISA notes
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

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.

Severity

CVSS 3.1 · CNA8.1 HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N/E:F/RL:O/RC:C

SSVC · CISA-ADP

Exploitationactive

Automatableno

Technical impacttotal

Exploitation Context

as of October 14, 2026

All KEV statistics→

CISA added CVE-2026-42897 to the KEV catalog 1 day after its CVE record was published. The median for entries added in 2026 so far is 15 days.
It is one of 391 Microsoft entries in the CISA KEV catalog, and one of 40 added in 2026.
Its current EPSS score (0.5%) is higher than that of 1% of CISA KEV entries.

Affected Products

Vendor	Product	Affected versions
Microsoft	Microsoft Microsoft Exchange Server 2016 Cumulative Update 23	15.01.0.0 to <15.01.2507.069
Microsoft	Microsoft Microsoft Exchange Server 2019 Cumulative Update 14	15.02.0.0 to <15.02.1544.041
Microsoft	Microsoft Microsoft Exchange Server 2019 Cumulative Update 15	15.02.0.0 to <15.02.1748.046
Microsoft	Microsoft Microsoft Exchange Server Subscription Edition RTM	15.02.0.0 to <15.02.2562.043

References

1 Links

Vendor advisories

Microsoft Exchange Server Spoofing Vulnerability

Record Details

Published

2026-05-14

Last updated

2026-08-10

Assigner (CNA)

microsoft

Credited to

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Tool categories

Application Security Tools Penetration Testing Tools

CVE record data © The MITRE Corporation, used under the CVE Terms of Use. Exploited-in-the-wild data from the CISA Known Exploited Vulnerabilities catalog (CC0). Exploit prediction scores by FIRST EPSS (first.org/epss). This site is not endorsed or certified by MITRE, NVD, CISA, or FIRST.

CVE-2026-42897