Known exploited vulnerability
CVE-2026-42897
The short answer
CVE-2026-42897 affects Microsoft Microsoft Exchange Server 2016 Cumulative Update 23 and is rated medium (CVSS 6.1). CISA added it to the Known Exploited Vulnerabilities catalog on 2026-05-15: attackers are using it, so patch it first.
What it is
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.
Weakness: CWE-79.
Severity
6.1 medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Exploited (CISA KEV)
Yes, since May 15, 2026
Federal due date May 29, 2026
EPSS, next 30 days
71%
Higher than 99% of scored CVEs
How it can be exploited
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- Required
- Scope
- Changed
- Confidentiality impact
- Low
- Integrity impact
- Low
- Availability impact
- None
What CISA says to do
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Affected products
Microsoft Exchange Server 2016 Cumulative Update 23, Microsoft Exchange Server 2019 Cumulative Update 14, Microsoft Exchange Server 2019 Cumulative Update 15, Microsoft Exchange Server Subscription Edition RTM. NVD's record lists the exact affected versions.
References
- msrc.microsoft.com/update-guide/vulnerability/CVE-2026-42897 MitigationVendor Advisory
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-42897 US Government Resource
Questions
Is CVE-2026-42897 being exploited?
Yes. CISA added CVE-2026-42897 to its Known Exploited Vulnerabilities catalog on 2026-05-15, with a federal remediation due date of 2026-05-29.
How do I fix CVE-2026-42897?
CISA's 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.
From NVD, CISA KEV, FIRST EPSS and OSV.dev, checked . Status on NVD: Analyzed. The description is NVD's text, quoted as published.
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