How severe is CVE-2021-27078?

CVE-2021-27078 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-27078 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 18% (97th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-27078?

CVE-2021-27078 primarily affects Microsoft Exchange Server. In total, 5 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-27078?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-27078 published?

CVE-2021-27078 was published on 2021-03-03 and last updated on 2026-06-17.

CVE-2021-27078

CVE-2021-27078 is a critical-severity vulnerability in Microsoft Exchange Server with a CVSS 3.x base score of 9.1. Its EPSS exploit-prediction score of 18% places it in the 97th percentile, indicating an elevated likelihood of exploitation.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
CVSS v2: 6.5
EPSS exploit prediction: 18% (97th percentile)
Actively exploited: Not listed in CISA KEV
Affected product: Microsoft Exchange Server
Published: 2021-03-03
Last modified: 2026-06-17

Description

Microsoft Exchange Server Remote Code Execution Vulnerability

Frequently asked questions

What is CVE-2021-27078?: Microsoft Exchange Server Remote Code Execution Vulnerability
How severe is CVE-2021-27078?: CVE-2021-27078 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-27078 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 18% (97th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-27078?: CVE-2021-27078 primarily affects Microsoft Exchange Server. In total, 5 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-27078?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-27078 published?: CVE-2021-27078 was published on 2021-03-03 and last updated on 2026-06-17.

References

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-27078

Affected products (5)

cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_18:*:*:*:*:*:*
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_7:*:*:*:*:*:*
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*

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