CVE-2021-27054

Code execution via XLS parser use-after-free

Published Mar 11, 2021 · Updated Aug 19, 2026

Use-after-free in Microsoft Excel allows remote attackers to execute code by opening a crafted XLS file in an affected Office product. The XLS parser performs operations on an object without first validating that the object still exists. Exploitation requires the target to visit a malicious page or open the file, and code runs in the current process context.

CVSS severity7.8
High
EPSS probability4.05%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in Microsoft Excel allows remote attackers to execute code by opening a crafted XLS file in an affected Office product. The XLS parser performs operations on an object without first validating that the object still exists. Exploitation requires the target to visit a malicious page or open the file, and code runs in the current process context.

The record

CVE
CVE-2021-27054
Published
Mar 11, 2021
Updated
Aug 19, 2026
Vendor
Microsoft
Product
Microsoft Office 2016
Classifications
T1203, T1204.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 11, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 19, 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=16.0.0 <16.0.5134.1000

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Microsoft · Microsoft Office 2016version=16.0.0 <16.0.5134.1000
Microsoft · Microsoft Office 2019version=19.0.0 <https://aka.ms/OfficeSecurityReleases
Microsoft · Microsoft Excel 2016version=16.0.0.0 <16.0.5134.1000
Microsoft · Microsoft Excel 2010version=13.0.0.0 <14.0.7266.5000
Microsoft · Microsoft Office 2013version=15.0.0 <publication
Microsoft · Microsoft Excel 2013version=15.0.0.0 <publication
Microsoft · Microsoft Office 2019 for Macversion=16.0.0 <publication
Microsoft · Microsoft Office Online Serverversion=16.0.1 <16.0.10372.20000
Microsoft · Microsoft Office Web Apps Server 2013version=15.0.1 <15.0.5327.1000
Microsoft · Microsoft Office 2010version=13.0.0.0 <14.0.7266.5000
Microsoft · Microsoft 365 Apps for enterpriseversion=16.0.1 <https://aka.ms/OfficeSecurityReleases

Published CVSS scores

7.8NISTCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

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

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

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Your stack

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