How severe is CVE-2021-43255?

CVE-2021-43255 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2021-43255 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (78th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-43255?

CVE-2021-43255 primarily affects Microsoft 365 Apps. In total, 11 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-43255?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-43255 published?

CVE-2021-43255 was published on 2021-12-15 and last updated on 2026-06-17.

CVE-2021-43255

CVE-2021-43255 is a medium-severity vulnerability in Microsoft 365 Apps with a CVSS 3.x base score of 5.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low.

Key facts

Severity: Medium (CVSS 3.x base score 5.5)
CVSS v2: 4.3
EPSS exploit prediction: 2% (78th percentile)
Actively exploited: Not listed in CISA KEV
Affected product: Microsoft 365 Apps
Published: 2021-12-15
Last modified: 2026-06-17

Description

Microsoft Office Trust Center Spoofing Vulnerability

Frequently asked questions

What is CVE-2021-43255?: Microsoft Office Trust Center Spoofing Vulnerability
How severe is CVE-2021-43255?: CVE-2021-43255 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2021-43255 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (78th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-43255?: CVE-2021-43255 primarily affects Microsoft 365 Apps. In total, 11 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-43255?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-43255 published?: CVE-2021-43255 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-2021-43255

Affected products (11)

cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x64:*
cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x86:*
cpe:2.3:a:microsoft:office:2013:sp1:*:*:*:*:x64:*
cpe:2.3:a:microsoft:office:2013:sp1:*:*:*:*:x86:*
cpe:2.3:a:microsoft:office:2013_rt:sp1:*:*:*:*:*:*
cpe:2.3:a:microsoft:office:2016:*:*:*:*:*:x64:*
cpe:2.3:a:microsoft:office:2016:*:*:*:*:*:x86:*
cpe:2.3:a:microsoft:office:2019:*:*:*:*:*:x64:*
cpe:2.3:a:microsoft:office:2019:*:*:*:*:*:x86:*
cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:*:x64:*
cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:*:x86:*

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