Summary
Impact: Spoofing. Microsoft rating: Important. Not known to be exploited — Exploitation Less Likely. Customer action: Required.
Details
According to the CVSS metrics, successful exploitation of this vulnerability could lead to some loss of confidentiality (C:L), and integrity (I:L) but lead to no loss of availability (A:N). What is the impact of this vulnerability?
An attacker who successfully exploited the vulnerability could view some sensitive information (Confidentiality), make changes to disclosed information (Integrity), but cannot limit access to the resource (Availability).
Why are update links missing for some Exchange products?
For Exchange Server 2016 and 2019, update links are not provided because these versions are out of support and security updates are only available through the Extended Security Update (ESU) program.
Customers enrolled in ESU can access the December 2025 and future updates, while those not enrolled should migrate to Exchange Server Subscription Edition (SE) to continue receiving security updates. If you have purchased ESU and need assistance accessing updates, contact Microsoft at **ExchangeandSfBServerESUInquiry@service.microsoft.com. **
For more details, see the official blog post.
Security updates
15.02.2562.037 — https://support.microsoft.com/help/5074992
15.01.2507.066 — https://support.microsoft.com/help/5074995
15.02.1748.043 — https://support.microsoft.com/help/5074993
15.02.1544.039 — https://support.microsoft.com/help/5074994
Vulnerabilities 1
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Medium 6.5
Microsoft Exchange Server Spoofing Vulnerability
User interface (ui) misrepresentation of critical information in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.
Revision history
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#1
Information published.
References
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CVE-2026-21527 Microsoft Exchange Server Spoofing Vulnerability - HTML
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21527
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Microsoft Exploitability Index
https://www.microsoft.com/en-us/msrc/exploitability-index?rtc=1
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Microsoft Support Lifecycle
https://support.microsoft.com/lifecycle
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Common Vulnerability Scoring System
https://www.first.org/cvss