CVE-2021-38655: microsoft 365_apps Use After Free
CVSS: 7.8v3.1HighModified
Published 15-09-2021Last modified 10-08-2026
Vulnerability summary
CVE-2021-38655 is a high (CVSS 7.8) Use After Free vulnerability in microsoft 365_apps. EPSS estimates a 6.39% chance of exploitation in the next 30 days, higher than 93.5% of scored vulnerabilities.
CVSS score
7.8/10
010
High · v3.1 (CVE.org)EPSS score
6.39%
0%100%
Low · +0.05 pp in 30 daysKEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded
Timeline
- 15-09-2021PublishedVulnerability first disclosed.
- 10-08-2026Last modifiedVulnerability information updated.
Description
Microsoft Excel 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
6.39%
Chance of exploitation in the next 30 days
Percentile
94%
Versus all other CVEs
30-day change
+0.05 pp
From 6.33% on 19-09-2026
19-09-202619-10-2026
EPSS score6.39%
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Microsoft12 products
- 365_appsna
- excel2013 | 2013:sp1 | 2016
- microsoft 365 apps for enterprise≥ 16.0.1, < https://aka.ms/OfficeSecurityReleases
- microsoft excel 2013 service pack 1≥ 15.0.0.0, < 5381.1000
- microsoft excel 2016≥ 16.0.0.0, < 5215.1000
1 vendor · 12 products
References
3 links
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-38655X Refsource MISCX TransferredPatchVendor Advisory
- www.zerodayinitiative.com/advisories/ZDI-21-1080/X Refsource MISCX TransferredThird Party AdvisoryVDB Entry