Which products and versions are affected by CVE-2021-34478?

Affected: 365 Apps (Microsoft); Office (Microsoft) versions 2019. The full list is in the CVE brief.

Is CVE-2021-34478 being exploited in the wild?

It is not listed in any known-exploited vulnerabilities catalog.

Is CVE-2021-34478 in the CISA KEV catalog?

No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.

Is there a public exploit for CVE-2021-34478?

No public exploit code is known.

How urgently should CVE-2021-34478 be patched?

Brandefense priority: patch immediately, because it is very likely to be exploited soon.

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Vulnerability Intelligence

CVE-2021-34478

High

Microsoft Office Remote Code Execution Vulnerability

Published Aug 12, 2021 · Updated Aug 10, 2026

Key Facts

Patch immediately

CVE-2021-34478 is a high-severity vulnerability (CVSS 7.8 v3.1) affecting 365 Apps (Microsoft), Office (Microsoft).
It is not listed in any known-exploited vulnerabilities catalog. No public exploit code is known.
EPSS estimates a 52% probability of exploitation in the next 30 days.
Fixed versions are available, including 365 Apps https://aka.ms/OfficeSecurityReleases, Office https://aka.ms/OfficeSecurityReleases.
Brandefense priority: patch immediately, because it is very likely to be exploited soon.

CVSS v3.1

7.8

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

EPSS (30-day exploit likelihood)

52%

Higher than 98.9% of all scored CVEs

Exploited in the wild

No known

Not in a known-exploited catalog

Public exploit code

None known

Get the full CVE-2021-34478 brief as a PDF

Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.

Description

Microsoft Office Remote Code Execution Vulnerability

Affected Products

2 affected entries in total

Product	Affected versions	Fixed in
365 AppsMicrosoft	See advisory	https://aka.ms/OfficeSecurityReleases
OfficeMicrosoft	2019	https://aka.ms/OfficeSecurityReleases

Patched Releases

365 Apps

https://aka.ms/OfficeSecurityReleases

Office

https://aka.ms/OfficeSecurityReleases

Timeline

Publicly disclosed
Aug 12, 2021
Last updated
Aug 10, 2026

References

FAQ

Common Questions.

Microsoft Office Remote Code Execution Vulnerability
Affected: 365 Apps (Microsoft); Office (Microsoft) versions 2019. The full list is in the CVE brief.
It is not listed in any known-exploited vulnerabilities catalog.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
No public exploit code is known.
Fixed versions are available, including 365 Apps https://aka.ms/OfficeSecurityReleases, Office https://aka.ms/OfficeSecurityReleases.
Brandefense priority: patch immediately, because it is very likely to be exploited soon.

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