CVE-2021-34438Network attack vector

Remote code execution via crafted font parsing

Published Jul 16, 2021 · Updated Aug 10, 2026

Remote code execution in Microsoft Windows Font Driver Host on affected Windows versions allows remote attackers to execute code via crafted fonts. The font-driver host improperly processes specially crafted font data, allowing attacker-controlled instructions to reach code execution when the data is opened or rendered. Exploitation requires user interaction with malicious font content; successful exploitation can compromise confidentiality, integrity, and availability.

CVSS severity6.8
Medium
EPSS probability2.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Remote code execution in Microsoft Windows Font Driver Host on affected Windows versions allows remote attackers to execute code via crafted fonts. The font-driver host improperly processes specially crafted font data, allowing attacker-controlled instructions to reach code execution when the data is opened or rendered. Exploitation requires user interaction with malicious font content; successful exploitation can compromise confidentiality, integrity, and availability.

The record

CVE
CVE-2021-34438
Published
Jul 16, 2021
Updated
Aug 10, 2026
Vendor
Microsoft
Product
Windows Server 2019
Classifications
T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 16, 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

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=10.0.17763.0 <10.0.17763.2061

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Windows Server 2019version=10.0.17763.0 <10.0.17763.2061
Microsoft · Windows 10 Version 21H1version=10.0.0 <10.0.19043.1110
Microsoft · Windows 10 Version 1909version=10.0.0 <10.0.18363.1679
Microsoft · Windows Server, version 2004version=10.0.0 <10.0.19041.1110
Microsoft · Windows 10 Version 20H2version=10.0.0 <10.0.19042.1110
Microsoft · Windows Server 2019 (Server Core installation)version=10.0.17763.0 <10.0.17763.2061
Microsoft · Windows Server version 20H2version=10.0.0 <10.0.19042.1110
Microsoft · Windows 10 Version 2004version=10.0.0 <10.0.19041.1110
Microsoft · Windows 10 Version 1809version=10.0.0 <10.0.17763.2061; version=10.0.17763.0 <10.0.17763.2061

Published CVSS scores

7.8[email protected]CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8[email protected]AV:N/AC:M/Au:N/C:P/I:P/A:P
7.8[email protected]CVSS: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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 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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