Is CVE-2021-34523 in the CISA KEV catalog?

Yes. CVE-2021-34523 is on the CISA Known Exploited Vulnerabilities list, added 2021-11-03, and has known ransomware campaign use.

What is the CVSS severity of CVE-2021-34523?

CVE-2021-34523 has a CVSS v3 base score of 9.0 (CRITICAL).

What is the EPSS score for CVE-2021-34523?

CVE-2021-34523 has an EPSS score of 99.99% (100th percentile), estimating the probability of exploitation in the next 30 days.

CVE & CISA-KEV Catalog

CVE-2021-34523

CRITICALCISA KEVEPSS 100th pctl

9.0

CVSS v3

NVD

Description

Microsoft Exchange Server Elevation of Privilege Vulnerability

CVSS v3 Vector

Exploitability

Attack VectorLocal

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeChanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityNone

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

Exploit Intelligence

99.99%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 Privilege Escalation Vulnerability

Microsoft Exchange Server contains an unspecified vulnerability that allows for privilege escalation.

Apply updates per vendor instructions.

Remediation due: 2021-11-17

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.