Cyber Resilience

CVE-2021-31166

Memory Safety in Microsoft Windows 10 2004 ≤ 10.0.19041.982

CISA KEVActive ExploitationEUVD ExploitedPublic PoCMemory Safety
Published
11 May 2021
Modified
30 October 2025
KEV Added
06 April 2022
Patch / advisory
View advisory
CVSS Score v3.1 9.8
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS Score 0.99 99.9th percentile
Risk Priority 97 floored blend · peak EPSS

Summary

CVE-2021-31166 is a critical-severity Use After Free (CWE-416) vulnerability in Microsoft Windows 10 2004. Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Client Execution (T1203); ranked in the top 0.1% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog; a public proof-of-concept is referenced.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2021-31166 is a remote code execution vulnerability in the HTTP Protocol Stack, tracked under CWE-416 for use-after-free conditions and carrying a CVSS 3.1 base score of 9.8 reflecting network-accessible attack complexity that is low with no privileges or user interaction required.

An unauthenticated remote attacker can send specially crafted HTTP requests to trigger the flaw, resulting in arbitrary code execution that impacts confidentiality, integrity, and availability on the affected system.

Microsoft's security advisory at portal.msrc.microsoft.com and the CISA Known Exploited Vulnerabilities catalog both reference this issue, directing administrators to apply the corresponding security updates for mitigation.

The entry's presence in the CISA catalog confirms observed real-world exploitation activity.

EU & UK References

Vulnerability Data

HTTP Protocol Stack Remote Code Execution Vulnerability

CWE(s)
CWE-416
KEV Date Added
06 April 2022

Related Threats

MITRE ATT&CK Enterprise Techniques

T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2021-34486Same product: Microsoft Windows 10 2004both on KEV
CVE-2021-40449Same product: Microsoft Windows 10 2004both on KEV
CVE-2021-26411Same product: Microsoft Windows 10 2004both on KEV
CVE-2023-21674Same product: Microsoft Windows 10 20H2both on KEV
CVE-2025-62221Same vendor: Microsoftboth on KEV
CVE-2010-0249Same vendor: Microsoftboth on KEV
CVE-2020-0674Same vendor: Microsoftboth on KEV
CVE-2012-4792Same vendor: Microsoftboth on KEV
CVE-2014-0322Same vendor: Microsoftboth on KEV
CVE-2010-3962Same vendor: Microsoftboth on KEV

Affected Assets

microsoft
windows 10 2004
≤ 10.0.19041.982
microsoft
windows 10 20h2
≤ 10.0.19042.982
microsoft
windows server 2004
≤ 10.0.19041.982
microsoft
windows server 20h2
≤ 10.0.19042.982

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 3 hardening rules · 3 OS baselines
Validate
Prove the fix (OWASP ASVS)
  • V1.4.3

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

SI-16 Memory Protection
addresses: CWE-416

Use-after-free exploits that achieve arbitrary code execution are blocked or significantly hardened by non-executable pages and ASLR.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly incorporate memory-safety tooling and reviews that prevent most use-after-free defects.

ID.RA-01 partial match
prevents

Vulnerability identification processes can discover use-after-free issues via scanning or analysis but do not prevent their introduction.

PR.PS-02 partial match
prevents

Routine patching removes known use-after-free instances after they have been introduced in released software.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing in development can detect use-after-free bugs before release.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC mandates memory-safety practices that reduce use-after-free defects.

A.8.26 Application security requirements partial match
prevents

Application security requirements can specify memory-management rules that mitigate use-after-free.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles include memory-safety design choices that limit use-after-free exposure.

A.8.28 Secure coding partial match
prevents

Secure coding standards directly prescribe avoidance of use-after-free patterns.

A.8.32 Change management partial match
prevents

Change-management processes help ensure memory-safety fixes are deployed consistently.

Hardening callouts derived

Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).

Oracle Linux 8 (1 rule)
  • V-248592 OL 8 must clear memory when it is freed to prevent use-after-free attacks. prevents CWE-416
RHEL 8 (1 rule)
  • V-230279 RHEL 8 must clear memory when it is freed to prevent use-after-free attacks. prevents CWE-416
RHEL 9 (1 rule)
  • V-257794 RHEL 9 must clear memory when it is freed to prevent use-after-free attacks. prevents CWE-416

References