Is CVE-2026-21527 in the CISA KEV catalog?

No. CVE-2026-21527 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-21527?

CVE-2026-21527 has a CVSS v3 base score of 6.5 (Important).

What is the EPSS score for CVE-2026-21527?

CVE-2026-21527 has an EPSS score of 7.68% (94th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-21527?

Install KB5074995 for Microsoft Exchange Server 2016 Cumulative Update 23. Fixes are available for 4 affected products.

CVE & CISA-KEV Catalog

CVE-2026-21527

HIGHEPSS 94th pctl

6.5

CVSS v3

NVD

Description

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

CWE-345 CWE-451 CWE-1286

How to fix

Remediation Available

Microsoft Exchange Server 2016 Cumulative Update 23Microsoft

Install:KB5074995

Microsoft Exchange Server 2019 Cumulative Update 14Microsoft

Install:KB5074994

Microsoft Exchange Server 2019 Cumulative Update 15Microsoft

Install:KB5074993

Microsoft Exchange Server Subscription Edition RTMMicrosoft

Install:KB5074992Microsoft

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityLow

IntegrityLow

AvailabilityNone

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

Exploit Intelligence

7.68%probability of exploitation in 30 days

94thpercentile

High risk: more likely to be exploited than 94% of all known CVEs.

References

Vendor Advisory1

msrc.microsoft.com

Related Vulnerabilities

Other CWE-345 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2023-38831	High	7.8	98%	KEV + Ransom	Fix
CVE-2016-4553	High	8.6	80%	-	Fix
CVE-2016-4554	High	8.6	39%	-	Fix
CVE-2023-35719	Medium	6.8	26%	-	-
CVE-2022-26871	Critical	9.8	20%	KEV	-
CVE-2014-4936	High	9.3	17%	-	-

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-15.