CVE-2021-34451Network attack vector

Unauthenticated information exposure via undisclosed spoofing

Published Jul 16, 2021 · Updated Aug 10, 2026

Spoofing in Microsoft Office Online Server 16.0.1 before 16.0.10376.20001 allows remote attackers to read limited information via network requests. Microsoft has not published the affected component, request field, or incorrect operation that causes the server to spoof content. Network access without authentication or user interaction is sufficient, and the published impact is limited to confidentiality.

CVSS severity5.3
Medium
EPSS probability1.78%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Spoofing in Microsoft Office Online Server 16.0.1 before 16.0.10376.20001 allows remote attackers to read limited information via network requests. Microsoft has not published the affected component, request field, or incorrect operation that causes the server to spoof content. Network access without authentication or user interaction is sufficient, and the published impact is limited to confidentiality.

The record

CVE
CVE-2021-34451
Published
Jul 16, 2021
Updated
Aug 10, 2026
Vendor
Microsoft
Product
Microsoft Office Online Server
Classifications
Unavailable
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 16, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=16.0.1 <16.0.10376.20001

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Microsoft Office Online Serverversion=16.0.1 <16.0.10376.20001

Published CVSS scores

5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
5.3Microsoft CorporationCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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