What is the CVSS score of CVE-2021-31166?

CVE-2021-31166 has a CVSS 3.1 base score of 9.8 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 99.7%.

Is there a public PoC exploit available for CVE-2021-31166?

Yes, a public proof-of-concept exploit is available for CVE-2021-31166. Prioritise patching immediately. EPSS: 99.7%.

Is there a patch available for CVE-2021-31166?

Yes, a patch is available for CVE-2021-31166. Update the affected software to the latest version immediately.

Windows 10 20H2 CVE-2021-31166

CRITICAL

Use After Free (CWE-416)

2021-05-11 secure@microsoft.com

RCE Use After Free Memory Corruption Microsoft Windows 10 20H2 Windows Server 2004 Windows 10 2004 Windows Server 20H2

9.8

CVSS 3.1 · Vendor: microsoft

Severity by source

Vendor (microsoft) PRIMARY

9.8 CRITICAL

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Primary rating from Vendor (microsoft) · only source for this CVE.

CVSS VectorVendor: microsoft

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Added to CISA KEV

Jul 14, 2026 - 04:22 CISA

CVE Published

May 11, 2021 - 19:15 cve.org

CRITICAL 9.8

DescriptionCVE.org

HTTP Protocol Stack Remote Code Execution Vulnerability

AnalysisAI

HTTP Protocol Stack Remote Code Execution Vulnerability. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. This Use After Free vulnerability could allow attackers to access freed memory to execute arbitrary code or crash the application.

Technical ContextAI

This vulnerability is classified as Use After Free (CWE-416), which allows attackers to access freed memory to execute arbitrary code or crash the application. Affected products include: Microsoft Windows 10 2004, Microsoft Windows 10 20H2, Microsoft Windows Server 2004, Microsoft Windows Server 20H2.

RemediationAI

A vendor patch is available. Apply the latest security update as soon as possible. Use smart pointers or garbage-collected languages. Set pointers to NULL after freeing. Enable memory sanitizers.