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Windows CVE-2026-20810

HIGH
Free of Memory not on the Heap (CWE-590)
2026-01-13 secure@microsoft.com
Windows Microsoft Windows 10 1809 Windows 10 21h2 Windows 10 22h2 Windows Server 2019
7.8
CVSS 3.1 · NVD
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Authenticate locally on Windows system
  2. Delivery
    Trigger memory deallocation vulnerability in Ancillary Function Driver
  3. Exploit
    Free non-heap memory region
  4. Execution
    Corrupt kernel data structures
  5. Impact
    Achieve privilege escalation to SYSTEM

Vulnerability Assessment

Weakness
CWE
CWE-590
OWASP Top 10:2025
A06:2021 - Vulnerable and Outdated Components
ASVS 5.0
V15 - Secure Coding and Architecture Free memory management
Exploitation Conditions

Local authenticated user account required on Windows system with Ancillary Function Driver for WinSock enabled. Attacker must have ability to invoke vulnerable driver functions through legitimate local access.
Impact

CVSS 7.8 (HIGH). Attack vector: Local. Complexity: Low. Privileges required: Low. User interaction: None. Exploitable via local access.
Exploit ScenarioDerived

An attacker could exploit this vulnerability to compromise the affected system.
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 12, 2026

The Windows Ancillary Function Driver for WinSock contains an improper memory deallocation vulnerability (CWE-590) that allows authenticated local attackers to achieve privilege escalation on affected Windows 10 and Windows Server 2019 systems. An attacker with local user privileges can exploit this flaw to gain SYSTEM-level access without user interaction. No patch is currently available for this vulnerability.

Earlier versions of this analysis (1)
v1 Mar 12, 2026 - 21:54 CVSS 7.8

Free of memory not on the heap in Windows Ancillary Function Driver for WinSock allows an authorized attacker to elevate privileges locally. [CVSS 7.8 HIGH]

RemediationAI

Monitor vendor advisories for a patch.

Affected Packages

microsoft windows_10_version_1809_10_0_17763_8276 fix: Windows 10 Version 1809 for 32-bit Systems 10.0.17763.8276, Windows 10 Version 1809 for x64-based Systems 10.0.17763.8276
microsoft windows_10_version_21h2_10_0_19044_6809 fix: Windows 10 Version 21H2 for 32-bit Systems 10.0.19044.6809, Windows 10 Version 21H2 for ARM64-based Systems 10.0.19044.6809, Windows 10 Version 21H2 for x64-based Systems 10.0.19044.6809
microsoft windows_10_version_22h2_10_0_19045_6809 fix: Windows 10 Version 22H2 for 32-bit Systems 10.0.19045.6809, Windows 10 Version 22H2 for ARM64-based Systems 10.0.19045.6809, Windows 10 Version 22H2 for x64-based Systems 10.0.19045.6809
microsoft windows_server_2019_10_0_17763_8276 fix: Windows Server 2019 10.0.17763.8276, Windows Server 2019 (Server Core installation) 10.0.17763.8276

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 4 packages in microsoft

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Technical ContextAI · show details

Affects the Windows Ancillary component of Windows 10 1809. Free of memory not on the heap in Windows Ancillary Function Driver for WinSock allows an authorized attacker to elevate privileges locally.

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  • Exploit and PoC references, threat intelligence from 22 sources
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Severity by source

NVD PRIMARY 7.8 HIGH
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

DescriptionCVE.org

Free of memory not on the heap in Windows Ancillary Function Driver for WinSock allows an authorized attacker to elevate privileges locally.

Executive ViewAI

Why It Matters

Organizations using Free of memory not on the heap in Windows Ancillary Function Driver for WinSock face notable risk from CVE-2026-20810 rated CVSS 7.8. Exploitation could compromise the security of affected deployments. Organizations should apply vendor updates when available and consider compensating controls in the interim.

Business Impact: High
Compensating Controls

Apply vendor patch. If immediate patching is not feasible: (1) Implement network-level access controls to limit exposure; (2) Enable enhanced monitoring and alerting; (3) Apply principle of least privilege.

Threat Intelligence Overview

EPSS Score
0.0%
Top 92% exploitable
Data Quality
3 sources
Confidence: Low
NVD CVE.org EPSS

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity HIGH
CISA KEV No
Public POC No
EPSS 0.0%
Patch available Yes
Active threat No
Deciding rule
HIGH severity (CVSS 7.0-8.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation· derived
None
System Exposure· derived
Small
Automatable· derived
No
Human Impact
High

Priority Score

39
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +39
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Affected Products (CPE)CVE.org

cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:x64:*
cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:x86:*
cpe:2.3:o:microsoft:windows_10_21h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_10_22h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2019:*:*:*:*:*:*:*:*

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References

Advisories & patches
ADVISORY https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20810

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