CVE-2021-26876Network attack vector

Remote code execution during OpenType font parsing

Published Mar 11, 2021 · Updated Aug 19, 2026

OpenType font parsing in Microsoft Windows allows remote attackers to execute code when a user processes crafted font content. Microsoft has not published the affected parser locus or the incorrect operation performed on the font data. Exploitation requires user interaction, and successful code runs with the privileges of the process handling the font.

CVSS severity8.8
High
EPSS probability2.71%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

OpenType font parsing in Microsoft Windows allows remote attackers to execute code when a user processes crafted font content. Microsoft has not published the affected parser locus or the incorrect operation performed on the font data. Exploitation requires user interaction, and successful code runs with the privileges of the process handling the font.

The record

CVE
CVE-2021-26876
Published
Mar 11, 2021
Updated
Aug 19, 2026
Vendor
Microsoft
Product
Windows Server 2019
Classifications
T1203
Attack vector
network
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=10.0.17763.0 <10.0.17763.1817

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Windows Server 2019version=10.0.17763.0 <10.0.17763.1817
Microsoft · Windows 10 Version 1909version=10.0.0 <10.0.18363.1440
Microsoft · Windows 10 Version 1803version=10.0.0 <10.0.17134.2087
Microsoft · Windows Server, version 2004version=10.0.0 <10.0.19043.867
Microsoft · Windows 10 Version 20H2version=10.0.0 <10.0.19043.867
Microsoft · Windows Server 2019 (Server Core installation)version=10.0.17763.0 <10.0.17763.1817
Microsoft · Windows Server version 20H2version=10.0.0 <10.0.19043.867
Microsoft · Windows 10 Version 2004version=10.0.0 <10.0.19043.867
Microsoft · Windows 10 Version 1809version=10.0.0 <10.0.17763.1817; version=10.0.17763.0 <10.0.17763.1817
Microsoft · Windows Server, version 1909 (Server Core installation)version=10.0.0 <10.0.18363.1440

Published CVSS scores

8.8Microsoft CorporationCVSS:3.1/AV:N/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

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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