CVE-2026-21527: Microsoft Exchange Server Spoofing Vulnerability

Overview

Severity
Medium (CVSS 6.5)
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N/E:U/RL:O/RC:C
Category
Spoofing
Exploit Status
Not Exploited
Exploitation Likelihood
Less Likely
Patch Tuesday
2026-Feb
Released
2026-02-10
EPSS Score
0.08% (percentile: 23.8%)

Description

User interface (ui) misrepresentation of critical information in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.

FAQ

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.

Affected Products (4)

Server Software

  • Microsoft Exchange Server Subscription Edition RTM

ESU

  • Microsoft Exchange Server 2016 Cumulative Update 23
  • Microsoft Exchange Server 2019 Cumulative Update 15
  • Microsoft Exchange Server 2019 Cumulative Update 14

Security Updates (1)

Acknowledgments

Vladislav Berghici of TrendAI Research, Vladislav Berghici of TrendAI Research

Revision History

  • 2026-02-10: Information published.