How severe is CVE-2021-43905?

CVE-2021-43905 has a CVSS 3.x base score of 9.6, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-43905 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (85th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-43905?

CVE-2021-43905 affects Microsoft 365 Copilot. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-43905?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-43905 published?

CVE-2021-43905 was published on 2021-12-15 and last updated on 2026-06-17.

CVE-2021-43905

CVE-2021-43905 is a critical-severity vulnerability in Microsoft 365 Copilot with a CVSS 3.x base score of 9.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low.

Key facts

Severity: Critical (CVSS 3.x base score 9.6)
CVSS v2: 6.8
EPSS exploit prediction: 3% (85th percentile)
Actively exploited: Not listed in CISA KEV
Affected product: Microsoft 365 Copilot
Published: 2021-12-15
Last modified: 2026-06-17

Description

Microsoft Office app Remote Code Execution Vulnerability

Frequently asked questions

What is CVE-2021-43905?: Microsoft Office app Remote Code Execution Vulnerability
How severe is CVE-2021-43905?: CVE-2021-43905 has a CVSS 3.x base score of 9.6, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-43905 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (85th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-43905?: CVE-2021-43905 affects Microsoft 365 Copilot. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-43905?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-43905 published?: CVE-2021-43905 was published on 2021-12-15 and last updated on 2026-06-17.

References

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43905

Affected products (1)

cpe:2.3:a:microsoft:365_copilot:*:*:*:*:*:*:*:*

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