What is the CVSS score of CVE-2026-21245?

CVE-2026-21245 has a CVSS 3.1 base score of 7.8 (High). CVSS vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 0.0%.

How to fix or mitigate CVE-2026-21245?

Within 24 hours: Inventory all Windows systems and identify those with high-value assets or sensitive data access; disable unnecessary local admin accounts and review privileged access policies. Within 7 days: Implement enhanced monitoring for privilege escalation attempts and restrict user-to-admin elevation capabilities where operationally feasible; segment critical systems on isolated networks. Within 30 days: Establish daily patch tracking for vendor updates; develop and test an emergency patching process for when the fix becomes available; conduct security awareness training on social engineering that could lead to authorized account compromise.

Windows CVE-2026-21245

HIGH

Heap-based Buffer Overflow (CWE-122)

2026-02-10 secure@microsoft.com

Windows Buffer Overflow Linux Heap Overflow Microsoft Windows 11 24h2 Windows 11 25h2 Windows Server 2025

7.8

CVSS 3.1 · NVD

View

Attack ChainAIDerived

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

Access

Craft malicious input to kernel API
Exploit

Trigger heap buffer overflow
Execution

Overwrite kernel memory structures
Impact

Execute arbitrary code with kernel privileges

Vulnerability Assessment

Weakness	CWE CWE-122 OWASP Top 10:2025 A06:2021 - Vulnerable and Outdated Components ASVS 5.0 V15 - Secure Coding and Architecture Heap buffer bounds checking MITRE ATT&CK 1 technique across 1 tactic: Execution The technique list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. Sign in to read
Exploitation Conditions	Attacker must have local login access to Windows system. No special kernel features required; exploitation occurs through standard kernel API calls available to authenticated local users on default Windows installations.
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

Windows Kernel heap overflow in Windows 11 25h2 and Windows Server 2025 enables authenticated local attackers to achieve privilege escalation with high impact on confidentiality, integrity, and availability. The vulnerability requires local access and user privileges but no user interaction, making it a practical attack vector for lateral movement within systems. No patch is currently available, leaving affected systems exposed until remediation is released.

Earlier versions of this analysis (1)

v1 Mar 12, 2026 - 22:02 CVSS 7.8

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

microsoft windows_11_version_24h2_10_0_26100_7840 fix: Windows 11 Version 24H2 for ARM64-based Systems 10.0.26100.7840, Windows 11 Version 24H2 for x64-based Systems 10.0.26100.7840

microsoft windows_11_version_25h2_10_0_26200_7840 fix: Windows 11 Version 25H2 for ARM64-based Systems 10.0.26200.7840, Windows 11 Version 25H2 for x64-based Systems 10.0.26200.7840

microsoft windows_11_version_26h1_10_0_28000_1575 fix: Windows 11 Version 26H1 for ARM64-based Systems 10.0.28000.1575, Windows 11 version 26H1 for x64-based Systems 10.0.28000.1575

microsoft windows_server_2025_10_0_26100_32370 fix: Windows Server 2025 10.0.26100.32370, Windows Server 2025 (Server Core installation) 10.0.26100.32370

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 4 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 11 24H2. 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

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

Heap-based buffer overflow in Windows Kernel allows an authorized attacker to elevate privileges locally.

Executive ViewAI

Why It Matters

A high-severity vulnerability in the Windows Kernel allows authenticated users to gain elevated system privileges, potentially enabling attackers to access sensitive data, deploy malware, or disrupt critical operations. This affects all Windows systems in your environment and requires immediate mitigation since no patch is currently available.

Business Impact: High

Compensating Controls

Apply principle of least privilege by removing unnecessary local administrator rights; implement application whitelisting to prevent unauthorized privilege escalation exploits; deploy endpoint detection and response (EDR) solutions with behavioral monitoring for suspicious privilege escalation patterns; enable Windows Event Log auditing (4672, 4673) to detect privilege use anomalies; restrict physical and remote access to high-risk systems; consider air-gapping critical infrastructure until patch availability; disable unnecessary Windows services and features to reduce attack surface.

Threat Intelligence Overview

EPSS Score

0.0%

Top 94% 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

Human Impact

High

Priority Score

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +39

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Buffer Overflow HIGH

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.

Heap Overflow HIGH

A heap overflow occurs when a program writes data beyond the bounds of a buffer allocated in the heap memory region.