CVE-2021-33776

Code execution through undisclosed media-processing flaw

Published Jul 14, 2021 · Updated Aug 10, 2026

Remote code execution in Microsoft HEVC Video Extensions before 1.0.41531.0 allows attackers to execute code after local user interaction. Microsoft has not published the decoder locus, malformed input condition, or incorrect operation that causes the flaw. Successful exploitation runs code in the affected media-processing context; the public assessment requires no prior privileges but does require user interaction.

CVSS severity7.8
High
EPSS probability2.36%
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 HEVC Video Extensions before 1.0.41531.0 allows attackers to execute code after local user interaction. Microsoft has not published the decoder locus, malformed input condition, or incorrect operation that causes the flaw. Successful exploitation runs code in the affected media-processing context; the public assessment requires no prior privileges but does require user interaction.

The record

CVE
CVE-2021-33776
Published
Jul 14, 2021
Updated
Aug 10, 2026
Vendor
Microsoft
Product
HEVC Video Extensions
Classifications
T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 14, 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=1.0.0 <1.0.41531.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Microsoft · HEVC Video Extensionsversion=1.0.0 <1.0.41531.0

Published CVSS scores

6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
7.8Microsoft CorporationCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
7.8NIST NVDCVSS: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

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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