Is CVE-2021-31209 in the CISA KEV catalog?

No. CVE-2021-31209 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-31209?

CVE-2021-31209 has a CVSS v3 base score of 6.5 (MEDIUM).

What is the EPSS score for CVE-2021-31209?

CVE-2021-31209 has an EPSS score of 2.63% (84th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-31209?

Install KB5003435 for Microsoft Exchange Server 2013 Cumulative Update 23. Fixes are available for 5 affected products.

CVE & CISA-KEV Catalog

CVE-2021-31209

MEDIUMEPSS 84th pctl

6.5

CVSS v3

NVD

Description

Microsoft Exchange Server Spoofing Vulnerability

CWE-290

How to fix

Remediation Available

Microsoft Exchange Server 2013 Cumulative Update 23Microsoft

Install:KB5003435Microsoft

Microsoft Exchange Server 2016 Cumulative Update 19Microsoft

Install:KB5003435Microsoft

Microsoft Exchange Server 2016 Cumulative Update 20Microsoft

Install:KB5003435Microsoft

Microsoft Exchange Server 2019 Cumulative Update 8Microsoft

Install:KB5003435Microsoft

Microsoft Exchange Server 2019 Cumulative Update 9Microsoft

Install:KB5003435Microsoft

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 ComplexityHigh

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityLow

AvailabilityNone

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

Exploit Intelligence

2.63%probability of exploitation in 30 days

84thpercentile

Elevated risk: more likely to be exploited than 84% of all known CVEs.

References

Patch1

portal.msrc.microsoft.com

Third-Party Advisory1

zerodayinitiative.com

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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 2025-02-28.