Is CVE-2021-42321 in the CISA KEV catalog?

Yes. CVE-2021-42321 is on the CISA Known Exploited Vulnerabilities list, added 2021-11-17, and has known ransomware campaign use.

What is the CVSS severity of CVE-2021-42321?

CVE-2021-42321 has a CVSS v3 base score of 8.8 (HIGH).

What is the EPSS score for CVE-2021-42321?

CVE-2021-42321 has an EPSS score of 90.39% (100th percentile), estimating the probability of exploitation in the next 30 days.

CVE & CISA-KEV Catalog

CVE-2021-42321

HIGHCISA KEVEPSS 100th pctl

8.8

CVSS v3

NVD

Description

Microsoft Exchange Server Remote Code Execution Vulnerability

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredLow

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Exploit Intelligence

90.39%probability of exploitation in 30 days

100thpercentile

Very high risk: more likely to be exploited than 100% of all known CVEs.

Known Exploited Vulnerability (CISA KEV)

Microsoft Exchange Server Remote Code Execution Vulnerability

An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.

Apply updates per vendor instructions.

Remediation due: 2021-12-01

Associated with ransomware campaigns

References

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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 2025-10-30.