What’s Vulnerable › Vulnerabilities

CVE-2021-34451: Microsoft Office Online Server Spoofing Vulnerability

• Severity: medium (CVSS 5.0 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-07-16 · updated 2026-08-10

Description

Microsoft Office Online Server Spoofing Vulnerability

Affected products

• Microsoft Office Online Server: all versions
• Microsoft Office Online Server: from 16.0.1 before 16.0.10376.20001 — fixed in 16.0.10376.20001

How to fix

Upgrade to a fixed version: Microsoft Office Online Server 16.0.10376.20001. Check the vendor advisory for mitigations.

References

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

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