CVE-2021-38656

Code execution via DOC parser use-after-free

Published Sep 15, 2021 · Updated Aug 10, 2026

Use-after-free in Word in Microsoft 365 Apps for enterprise allows remote attackers to execute code through a crafted DOC file. The DOC parser reuses a pointer after freeing its referenced memory when processing crafted document data, enabling code execution in the Word process. Exploitation requires a user to visit a malicious page or open the file, and successful code runs with that user's application privileges.

CVSS severity7.8
High
EPSS probability6.68%
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 Word in Microsoft 365 Apps for enterprise allows remote attackers to execute code through a crafted DOC file. The DOC parser reuses a pointer after freeing its referenced memory when processing crafted document data, enabling code execution in the Word process. Exploitation requires a user to visit a malicious page or open the file, and successful code runs with that user's application privileges.

The record

CVE
CVE-2021-38656
Published
Sep 15, 2021
Updated
Aug 10, 2026
Vendor
Microsoft
Product
Microsoft 365 Apps for enterprise
Classifications
CWE-416, T1204.002, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 10, 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=16.0.1 <https://aka.ms/OfficeSecurityReleases

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

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
T1204.002Malicious File
T1203Exploitation for Client Execution

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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