How severe is CVE-2021-34523?

CVE-2021-34523 has a CVSS 3.x base score of 9.0, rated critical severity. It is exploitable over local access with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2021-34523 being actively exploited?

Yes. CVE-2021-34523 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2021-11-03, which means active exploitation has been confirmed. It should be prioritised for remediation.

What products are affected by CVE-2021-34523?

CVE-2021-34523 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-2021-34523?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.

Does CVE-2021-34523 have an EU (EUVD) identifier?

Yes. CVE-2021-34523 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-21177. It is also flagged as exploited in the EUVD (since 2021-11-03).

When was CVE-2021-34523 published?

CVE-2021-34523 was published on 2021-07-14 and last updated on 2026-08-10.

CVE-2021-34523

CVE-2021-34523 is a critical-severity vulnerability in Microsoft Exchange Server with a CVSS 3.x base score of 9.0. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2021-11-03).

Key facts

Severity: Critical (CVSS 3.x base score 9.0)
CVSS v2: 7.5
EPSS exploit prediction: 100% (100th percentile)
Actively exploited: Yes — listed in CISA KEV (added 2021-11-03)
EU (EUVD) id: EUVD-2021-21177
EU exploitation: Flagged exploited in the ENISA EU Vulnerability Database (since 2021-11-03)
Affected product: Microsoft Exchange Server
Published: 2021-07-14
Last modified: 2026-08-10

Description

Microsoft Exchange Server Elevation of Privilege Vulnerability

Frequently asked questions

What is CVE-2021-34523?: Microsoft Exchange Server Elevation of Privilege Vulnerability
How severe is CVE-2021-34523?: CVE-2021-34523 has a CVSS 3.x base score of 9.0, rated critical severity. It is exploitable over local access with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2021-34523 being actively exploited?: Yes. CVE-2021-34523 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2021-11-03, which means active exploitation has been confirmed. It should be prioritised for remediation.
What products are affected by CVE-2021-34523?: CVE-2021-34523 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-2021-34523?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.
Does CVE-2021-34523 have an EU (EUVD) identifier?: Yes. CVE-2021-34523 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-21177. It is also flagged as exploited in the EUVD (since 2021-11-03).
When was CVE-2021-34523 published?: CVE-2021-34523 was published on 2021-07-14 and last updated on 2026-08-10.

References

Affected products (5)

cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_20:*:*:*:*:*:*
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_9:*:*:*:*:*:*

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Threat intelligence

Threat-intel indicators referencing this CVE:

85.50.130.150 (ipv4-addr)