What is the CVSS score of CVE-2025-21418?

CVE-2025-21418 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: 13.6%.

Is CVE-2025-21418 being actively exploited?

Yes, CVE-2025-21418 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, confirming active in-the-wild exploitation. Immediate patching is required.

How to fix or mitigate CVE-2025-21418?

Within 24 hours: Identify all affected systems and apply vendor patches immediately. If patching is delayed, consider network segmentation to limit exposure.

Windows CVE-2025-21418

HIGH

Heap-based Buffer Overflow (CWE-122)

2025-02-11 secure@microsoft.com

Windows Buffer Overflow Heap Overflow Microsoft Windows 10 1607 Windows 10 1809 Windows 10 21h2 Windows 10 22h2 Windows 11 22h2 Windows 11 23h2 Windows 11 24h2 Windows Server 2008 Windows Server 2012 Windows Server 2016 Windows Server 2019 Windows Server 2022 Windows Server 2022 23h2 Windows Server 2025

7.8

CVSS 3.1 · NVD

View

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Weakness	CWE CWE-122 OWASP Top 10:2025 A06:2021 - Vulnerable and Outdated Components ASVS 5.0 V15 - Secure Coding and Architecture Heap buffer bounds checking MITRE ATT&CK 1 technique across 1 tactic: Execution The technique list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
Impact	High risk (CVSS 7.8, EPSS 13.6%). AFD.sys is a perennial target for kernel exploitation. Zero-day exploitation in February 2025 indicates use by advanced threat actors. The driver's ubiquity ensures the vulnerability affects all Windows installations.
Exploit ScenarioDerived	After gaining initial access, an attacker uses the AFD.sys heap overflow to corrupt kernel objects and escalate to SYSTEM. The reliable exploitation path through Winsock operations makes this a preferred privilege escalation technique.

Act Now Prioritize within 24-48h. Why: In CISA KEV with patch available.

Exploited in the wild (CISA KEV) Patch available 13.6% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 28, 2026

Windows Ancillary Function Driver for WinSock contains a heap-based buffer overflow enabling local privilege escalation to SYSTEM, exploited in the wild in February 2025.

Earlier versions of this analysis (1)

v1 Mar 28, 2026 - 18:26 CVSS 7.8

A heap-based buffer overflow in Windows AFD.sys (Ancillary Function Driver for WinSock) allows local privilege escalation. Exploited as a zero-day in February 2025.

RemediationAI

Apply February 2025 Patch Tuesday update. Monitor for kernel exploitation indicators. Deploy Windows Defender Exploit Guard kernel protections.

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

The CWE-122 heap overflow in afd.sys allows local code to corrupt kernel heap memory through crafted Winsock operations. AFD.sys vulnerabilities are highly valued because the driver is always loaded and accessible from user mode without special privileges.

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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

Lifecycle Timeline

Patch released

Mar 28, 2026 - 18:26 nvd

Patch available

Added to CISA KEV

Oct 27, 2025 - 17:13 cisa

CISA KEV

CVE Published

Feb 11, 2025 - 18:15 nvd

HIGH 7.8

DescriptionCVE.org

Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability

Executive ViewAI

Why It Matters

CVE-2025-21418 presents notable security risk, a heap-based buffer overflow vulnerability rated CVSS 7.8. Exploitation could allow attackers to corrupt memory, crash the application, or potentially execute arbitrary code. This vulnerability is actively exploited in the wild (KEV-listed) and requires immediate remediation. A patch is available and should be applied as part of regular vulnerability management.

Business Impact: Severe

Compensating Controls

Apply vendor patch. If immediate patching is not feasible: (1) Enable ASLR and DEP where available; (2) Implement network segmentation; (3) Monitor for exploitation indicators.

Threat Intelligence Overview

EPSS Score

13.6%

Top 6% exploitable

Data Quality

4 sources

Confidence: Medium

NVD

CVE.org

CISA KEV

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 Yes

Public POC No

EPSS 13.6%

Patch available Yes

Active threat Yes

Deciding rule

In CISA KEV with patch available

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

Out-of-Cycle

Exploitation· derived

Active

System Exposure· derived

Small

Automatable· derived

Human Impact

Very High

Priority Score

103

Low Medium High Critical

KEV: +50

EPSS: +14

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.

Affected Products (CPE)CVE.org

cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:x64:*

cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:x86:*

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_11_22h2:*:*:*:*:*:*:*:*

cpe:2.3:o:microsoft:windows_11_23h2:*:*:*:*:*:*:*:*

cpe:2.3:o:microsoft:windows_11_24h2:*:*:*:*:*:*:*:*

cpe:2.3:o:microsoft:windows_server_2008:-:sp2:*:*:*:*:*:*

cpe:2.3:o:microsoft:windows_server_2008:r2:sp1:*:*:*:*:x64:*

cpe:2.3:o:microsoft:windows_server_2012:-:*:*:*:*:*:*:*

cpe:2.3:o:microsoft:windows_server_2012:r2:*:*:*:*:*:*:*

cpe:2.3:o:microsoft:windows_server_2016:*:*:*:*:*:*:*:*

cpe:2.3:o:microsoft:windows_server_2019:*:*:*:*:*:*:*:*

cpe:2.3:o:microsoft:windows_server_2022:*:*:*:*:*:*:*:*

cpe:2.3:o:microsoft:windows_server_2022_23h2:*:*:*:*:*:*:*:*

cpe:2.3:o:microsoft:windows_server_2025:*:*:*:*:*:*:*:*

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References

Advisories & patches

PATCH https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21418 REF https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-21418

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