CVE-2021-28454

Code execution via use-after-free during XLS parsing

Published Apr 13, 2021 · Updated Aug 3, 2024

Use-after-free in Microsoft Excel allows remote attackers to execute arbitrary code by convincing a target to open a crafted XLS file. Excel fails to validate that an object still exists before operating on it while parsing XLS content, leaving a stale object reference available for reuse. Exploitation requires a malicious page or file, and successful code runs in the current Excel process.

CVSS severity7.8
High
EPSS probability3.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Use-after-free in Microsoft Excel allows remote attackers to execute arbitrary code by convincing a target to open a crafted XLS file. Excel fails to validate that an object still exists before operating on it while parsing XLS content, leaving a stale object reference available for reuse. Exploitation requires a malicious page or file, and successful code runs in the current Excel process.

The record

CVE
CVE-2021-28454
Published
Apr 13, 2021
Updated
Aug 3, 2024
Vendor
Microsoft
Product
Microsoft Office 2016
Classifications
CWE-416, T1203, T1204.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 13, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=16.0.0 <publication

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Microsoft · Microsoft Office 2016version=16.0.0 <publication
Microsoft · Microsoft Office 2019version=19.0.0 <https://aka.ms/OfficeSecurityReleases
Microsoft · Microsoft Excel 2016version=16.0.0.0 <publication
Microsoft · Microsoft Excel 2010version=13.0.0.0 <publication
Microsoft · Microsoft Office 2013version=15.0.0 <publication
Microsoft · Microsoft Excel 2013version=15.0.0.0 <publication
Microsoft · Microsoft Office Online Serverversion=16.0.1 <publication
Microsoft · Microsoft Office Web Apps Server 2013version=15.0.1 <publication
Microsoft · Microsoft Office 2010version=13.0.0.0 <publication
Microsoft · Microsoft 365 Apps for enterpriseversion=16.0.1 <https://aka.ms/OfficeSecurityReleases

Published CVSS scores

7.8Microsoft CorporationCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P

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)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1203Exploitation for Client Execution
T1204.002Malicious File

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo