Windows
CVE-2026-21239
HIGH
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessCraft malicious local request
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DeliveryTrigger heap-based buffer overflow in Windows Kernel
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ExploitWrite arbitrary data to heap memory
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ExecutionEscape process sandbox
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ImpactExecute code with elevated privileges
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A06:2021 - Vulnerable and Outdated Components
ASVS 5.0
V15 - Secure Coding and Architecture Heap buffer bounds checking
MITRE ATT&CK
1 technique across 1 tactic: Execution The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Exploitation Conditions | Authenticated local user account required on Windows system. Attacker must have user-level privileges (PR:L) to invoke the vulnerable kernel code path. No special configuration required; vulnerability exists in default Windows Kernel implementations. |
| 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. |
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Alert meAnalysisAIv1 – Mar 12, 2026
Privilege escalation via heap buffer overflow in Windows Kernel (Windows 10 21H2, Windows Server 2016) allows authenticated local users to gain elevated system privileges. The vulnerability requires local access and user-level permissions, making it exploitable by authorized account holders to bypass security boundaries. No patch is currently available for this issue.
Earlier versions of this analysis (1)
Heap-based buffer overflow in Windows Kernel allows an authorized attacker to elevate privileges locally. [CVSS 7.8 HIGH]
RemediationAI
Monitor vendor advisories for a patch. Enable ASLR, DEP/NX, and stack canaries where possible.
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 14 packages in microsoft
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
Classified as CWE-122 (Heap-based Buffer Overflow). Affects Windows 10 1607. Heap-based buffer overflow in Windows Kernel 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
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
DescriptionCVE.org
Heap-based buffer overflow in Windows Kernel allows an authorized attacker to elevate privileges locally.
Executive ViewAI
A critical Windows Kernel vulnerability (CVE-2026-21239) allows authorized users with local system access to escalate their privileges to administrator level, potentially enabling lateral movement, data exfiltration, and system compromise. This poses a significant risk to organizational security posture as it requires no patch availability and affects core Windows infrastructure across the enterprise.
Implement strict privileged access management (PAM) controls restricting local administrator account usage; enforce multi-factor authentication for sensitive systems; disable unnecessary user accounts with local logon rights; deploy HIPS/HIES endpoint detection and response (EDR) tools with behavioral monitoring for privilege escalation patterns; segment critical systems to limit lateral movement if exploitation occurs; enable Windows audit logging for privilege escalation events; consider running critical applications in constrained user accounts with minimal privileges.
Threat Intelligence Overview
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.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.
A heap overflow occurs when a program writes data beyond the bounds of a buffer allocated in the heap memory region.
Affected Products (CPE)CVE.org
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GitHub PoC
Exploit-DB