CVE-2026-20936: Windows NDIS Information Disclosure Flaw

CVE-2026-20936 Overview

CVE-2026-20936 is an out-of-bounds read vulnerability in Windows Network Driver Interface Specification (NDIS) that allows an authorized attacker with physical access to disclose sensitive information. NDIS is a critical Windows component that provides a standard interface for network interface cards (NICs) and protocol drivers, making vulnerabilities in this subsystem particularly concerning for enterprise environments.

Critical Impact

An attacker with physical access and low-level authorization can leverage this out-of-bounds read to extract sensitive information from system memory, potentially exposing credentials, encryption keys, or other confidential data processed by the network stack.

Affected Products

• Windows NDIS (Network Driver Interface Specification)
• Windows Operating Systems with vulnerable NDIS implementations

Discovery Timeline

• January 13, 2026 - CVE-2026-20936 published to NVD
• January 13, 2026 - Last updated in NVD database

Technical Details for CVE-2026-20936

Vulnerability Analysis

This vulnerability is classified as CWE-125 (Out-of-bounds Read), a memory corruption issue where the affected code reads data from a memory location that is outside the intended buffer boundaries. In the context of Windows NDIS, this type of vulnerability occurs when the driver fails to properly validate buffer lengths or indices before performing memory read operations.

The physical attack vector requirement means an attacker must have direct physical access to the target system to exploit this vulnerability. While this limits the attack surface compared to remote vulnerabilities, it remains a significant concern for environments where physical security cannot be fully guaranteed, such as shared workspaces, data centers with contractor access, or situations involving insider threats.

The vulnerability enables information disclosure with high confidentiality impact, meaning an attacker could potentially read sensitive data from kernel memory, including network traffic buffers, authentication credentials, or cryptographic material handled by the NDIS layer.

Root Cause

The root cause of CVE-2026-20936 lies in improper bounds checking within the Windows NDIS component. The vulnerability occurs when the driver processes certain inputs without adequately validating that memory read operations remain within allocated buffer boundaries. This allows an attacker to craft malicious inputs that cause the driver to read from memory locations beyond the intended buffer, potentially accessing sensitive kernel memory contents.

Attack Vector

Exploitation of CVE-2026-20936 requires physical access to the target system along with low-level authorization. The attack scenario typically involves:

1. An attacker gains physical access to a Windows system with a vulnerable NDIS implementation
2. The attacker interacts with the network driver through specially crafted requests or by manipulating hardware interfaces
3. The vulnerable code path is triggered, causing an out-of-bounds memory read
4. Sensitive information from adjacent memory regions is disclosed to the attacker

The physical access requirement and need for authorization significantly reduces the exploitability compared to remote, unauthenticated vulnerabilities. However, the vulnerability remains relevant for threat models that include insider threats, stolen devices, or supply chain attacks.

Detection Methods for CVE-2026-20936

Indicators of Compromise

• Unusual or unauthorized physical access to systems, particularly targeting network interface hardware
• Anomalous NDIS driver behavior or unexpected memory access patterns in kernel debugging logs
• Evidence of specialized hardware tools or adapters connected to network interfaces
• Unexplained kernel mode exceptions or error logs related to NDIS components

Detection Strategies

• Deploy endpoint detection and response (EDR) solutions capable of monitoring kernel-level memory access patterns
• Implement hardware-based security monitoring to detect unauthorized physical access to network interfaces
• Enable detailed Windows event logging for driver loading and network subsystem activities
• Monitor for unusual privilege escalation attempts that could precede physical exploitation

Monitoring Recommendations

• Enable Windows Driver Framework verbose logging for NDIS-related drivers
• Configure security information and event management (SIEM) rules to alert on unusual NDIS driver events
• Implement physical security monitoring including camera surveillance and access logging for server rooms
• Conduct regular security audits of systems accessible to personnel with low-level authorization

How to Mitigate CVE-2026-20936

Immediate Actions Required

• Apply Microsoft security updates as soon as they become available through Windows Update or WSRC
• Restrict physical access to critical systems, especially those processing sensitive network traffic
• Review and limit user accounts with authorization levels that could enable exploitation
• Implement additional physical security controls such as USB port blockers and network interface locks

Patch Information

Microsoft has published a security update for this vulnerability. Administrators should apply the patch available through the Microsoft Security Update Guide. The update addresses the out-of-bounds read condition by implementing proper bounds validation in the affected NDIS code paths.

Organizations should prioritize patching based on the physical accessibility of their Windows systems and the sensitivity of data processed by those systems.

Workarounds

• Implement strict physical access controls to limit who can interact with vulnerable systems
• Use hardware security modules (HSMs) or Trusted Platform Module (TPM) features to protect sensitive cryptographic material
• Consider network segmentation to isolate systems that cannot be immediately patched from sensitive network segments
• Deploy additional monitoring solutions to detect unauthorized physical access attempts
• Evaluate the use of full-disk encryption and secure boot to limit the impact of physical attacks

# Enable detailed Windows event logging for driver activities
wevtutil sl Microsoft-Windows-NDIS/Operational /e:true

# Review current NDIS driver status and configuration
Get-NetAdapter | Get-NetAdapterAdvancedProperty

# Check for recent security updates related to NDIS
Get-HotFix | Where-Object {$_.Description -match "Security Update"} | Sort-Object InstalledOn -Descending