CVE-2021-31176

Code execution via XLS parser use-after-free

Published May 11, 2021 · Updated Aug 3, 2024

Use-after-free in Microsoft Excel in affected Microsoft Office editions allows remote attackers to execute code through a crafted XLS file. The XLS parser operates on an object without first validating that the object still exists, causing a use-after-free during file parsing. Exploitation requires a user to visit a malicious page or open a malicious file, and successful code runs in the current process context.

CVSS severity7.8
High
EPSS probability3.05%
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 in affected Microsoft Office editions allows remote attackers to execute code through a crafted XLS file. The XLS parser operates on an object without first validating that the object still exists, causing a use-after-free during file parsing. Exploitation requires a user to visit a malicious page or open a malicious file, and successful code runs in the current process context.

The record

CVE
CVE-2021-31176
Published
May 11, 2021
Updated
Aug 3, 2024
Vendor
Microsoft
Product
Microsoft Office 2016
Classifications
CWE-416, T1204.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 11, 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

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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 <16.0.5161.1002

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Microsoft · Microsoft Office 2016version=16.0.0 <16.0.5161.1002
Microsoft · Microsoft Office 2019version=19.0.0 <https://aka.ms/OfficeSecurityReleases
Microsoft · Microsoft Office 2013version=15.0.0 <15.0.5345.1002
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 National Vulnerability DatabaseAV: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
T1204.002User Execution: Malicious 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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