CVE-2021-34478: microsoft 365_apps
CVSS: 7.8v3.1HighModified
Published 12-08-2021Last modified 10-08-2026
Vulnerability summary
CVE-2021-34478 is a high (CVSS 7.8) vulnerability in microsoft 365_apps. EPSS estimates a 51.52% chance of exploitation in the next 30 days, higher than 98.9% of scored vulnerabilities.
CVSS score
7.8/10
010
High · v3.1 (CVE.org)EPSS score
51.52%
0%100%
Critical · +0.28 pp in 30 daysKEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded
Timeline
- 12-08-2021PublishedVulnerability first disclosed.
- 10-08-2026Last modifiedVulnerability information updated.
Description
Microsoft Office Remote Code Execution Vulnerability
CVSS metrics
3 scores · 2 sources · 2 versionsHigh 7.8Preferred score · CVE.org (CNA)
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:CSourcesAll 2 agree
- NVDNIST7.8HighCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Medium 6.8Preferred score · NVD (NIST)
AV:N/AC:M/Au:N/C:P/I:P/A:PSourcesSingle source
EPSS trend
Probability
51.52%
Chance of exploitation in the next 30 days
Percentile
99%
Versus all other CVEs
30-day change
+0.28 pp
From 51.24% on 22-09-2026
22-09-202622-10-2026
EPSS score51.52%
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeNo weakness data has been published for this record.
Affected systems
Microsoft4 products
- 365_appsna
- microsoft 365 apps for enterprise≥ 16.0.1, < https://aka.ms/OfficeSecurityReleases
- microsoft office 2019≥ 19.0.0, < https://aka.ms/OfficeSecurityReleases
- officeEOL2019
1 vendor · 4 products
References
3 links
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34478X Refsource MISCX TransferredPatchVendor Advisory
- www.zerodayinitiative.com/advisories/ZDI-21-1024/X Refsource MISCX TransferredThird Party AdvisoryVDB Entry