How severe is CVE-2026-21527?

CVE-2026-21527 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2026-21527 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 9% (95th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-21527?

CVE-2026-21527 primarily affects Microsoft Exchange Server. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-21527?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-21527 have an EU (EUVD) identifier?

Yes. CVE-2026-21527 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-7340.

When was CVE-2026-21527 published?

CVE-2026-21527 was published on 2026-02-10 and last updated on 2026-06-17.

CVE-2026-21527

CVE-2026-21527 is a medium-severity vulnerability in Microsoft Exchange Server with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-345.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
EPSS exploit prediction: 9% (95th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-7340
Weakness: CWE-345
Affected product: Microsoft Exchange Server
Published: 2026-02-10
Last modified: 2026-06-17

Description

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

Frequently asked questions

What is CVE-2026-21527?: User interface (ui) misrepresentation of critical information in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.
How severe is CVE-2026-21527?: CVE-2026-21527 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-21527 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 9% (95th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-21527?: CVE-2026-21527 primarily affects Microsoft Exchange Server. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-21527?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-21527 have an EU (EUVD) identifier?: Yes. CVE-2026-21527 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-7340.
When was CVE-2026-21527 published?: CVE-2026-21527 was published on 2026-02-10 and last updated on 2026-06-17.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21527

Affected products (4)

cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_23:*:*:*:*:*:*
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_14:*:*:*:*:*:*
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_15:*:*:*:*:*:*
cpe:2.3:a:microsoft:exchange_server_subscription_edition:*:*:*:*:*:*:*:*

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