Is CVE-2021-34520 in the CISA KEV catalog?

No. CVE-2021-34520 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-34520?

CVE-2021-34520 has a CVSS v3 base score of 8.1 (HIGH).

What is the EPSS score for CVE-2021-34520?

CVE-2021-34520 has an EPSS score of 3.32% (87th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-34520?

Install KB5001976 for Microsoft SharePoint Enterprise Server 2016. Fixes are available for 3 affected products.

CVE & CISA-KEV Catalog

CVE-2021-34520

HIGHEPSS 87th pctl

8.1

CVSS v3

NVD

Description

Microsoft SharePoint Server Remote Code Execution Vulnerability

CWE-502Deserialization of Untrusted Data

How to fix

Remediation Available

Microsoft SharePoint Enterprise Server 2016Microsoft

Install:KB5001976Microsoft

Microsoft SharePoint Foundation 2013 Service Pack 1Microsoft

Install:KB5001992Microsoft

Microsoft SharePoint Server 2019Microsoft

Install:KB5001975Microsoft

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 RequiredLow

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityNone

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

Exploit Intelligence

3.32%probability of exploitation in 30 days

87thpercentile

Elevated risk: more likely to be exploited than 87% of all known CVEs.

References

Patch1

portal.msrc.microsoft.com

Third-Party Advisory1

zerodayinitiative.com

Related Vulnerabilities

Other CWE-502 (Deserialization of Untrusted Data) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2023-0669	High	7.2	100%	KEV + Ransom	Fix
CVE-2021-44228	Critical	10.0	100%	KEV + Ransom	Fix
CVE-2021-35464	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2023-29300	Critical	9.8	100%	KEV + Ransom	-
CVE-2025-53770	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2022-47986	Critical	9.8	100%	KEV + Ransom	-

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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 2024-11-21.