How severe is CVE-2021-34451?

CVE-2021-34451 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.

Is CVE-2021-34451 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (74th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-34451?

CVE-2021-34451 affects Microsoft Office Online Server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-34451?

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

When was CVE-2021-34451 published?

CVE-2021-34451 was published on 2021-07-16 and last updated on 2026-06-17.

CVE-2021-34451

CVE-2021-34451 is a medium-severity vulnerability in Microsoft Office Online Server with a CVSS 3.x base score of 5.3. 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 5.3)
CVSS v2: 5.0
EPSS exploit prediction: 2% (74th percentile)
Actively exploited: Not listed in CISA KEV
Affected product: Microsoft Office Online Server
Published: 2021-07-16
Last modified: 2026-06-17

Description

Microsoft Office Online Server Spoofing Vulnerability

Frequently asked questions

What is CVE-2021-34451?: Microsoft Office Online Server Spoofing Vulnerability
How severe is CVE-2021-34451?: CVE-2021-34451 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.
Is CVE-2021-34451 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (74th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-34451?: CVE-2021-34451 affects Microsoft Office Online Server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-34451?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-34451 published?: CVE-2021-34451 was published on 2021-07-16 and last updated on 2026-06-17.

References

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34451

Affected products (1)

cpe:2.3:a:microsoft:office_online_server:-:*:*:*:*:*:*:*

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