CVE-2026-69548: Windows RNDIS Buffer Overflow Vulnerability

CVE-2026-69548 Overview

CVE-2026-69548 is a heap-based buffer overflow vulnerability in the Windows Remote Network Driver Interface Specification (RNDIS) component. The flaw allows an unauthorized attacker with physical access to a target device to disclose sensitive information from heap memory. The vulnerability is tracked under CWE-122: Heap-based Buffer Overflow and requires no authentication or user interaction to exploit.

Critical Impact
An attacker with physical access to a Windows device can trigger a heap overflow in the RNDIS driver to read confidential memory contents without user interaction or credentials.

Affected Products

Microsoft Windows (RNDIS driver component)
Refer to the Microsoft Security Update Guide for the complete list of affected Windows versions
Systems exposing USB or physical network interfaces that load the RNDIS driver

Discovery Timeline

2026-09-08 - CVE CVE-2026-69548 published to NVD
2026-09-08 - Last updated in NVD database

Technical Details for CVE-2026-69548

Vulnerability Analysis

The vulnerability resides in the Windows RNDIS driver, which implements a Microsoft protocol for exposing network devices over USB and other bus interfaces. A heap-based buffer overflow occurs when the driver processes attacker-controlled RNDIS messages received from a physically attached device. Because the parsing logic fails to correctly validate length fields, adjacent heap memory can be read outside the intended buffer boundary. The attack vector is physical, meaning the adversary must connect a malicious device such as a rogue USB gadget emulating an RNDIS network adapter.

Root Cause

The root cause is improper bounds checking in the RNDIS message-handling path within the kernel-mode driver. When a crafted control or data message specifies a length that exceeds the size of the allocated heap buffer, the driver processes memory beyond the buffer, exposing residual kernel or driver heap data. This behavior aligns with CWE-122, where the overflow occurs in a dynamically allocated region rather than the stack.

Attack Vector

Exploitation requires physical proximity to the target. An attacker connects a device that presents itself as an RNDIS-compatible network adapter, typically over USB. Windows loads the RNDIS driver automatically and begins parsing configuration and control messages. The malicious device then sends malformed RNDIS packets that trigger the overflow. The confidentiality impact is high, but integrity and availability are unaffected, indicating the primary exploitation outcome is information disclosure from kernel heap memory.

No public proof-of-concept code is available for this vulnerability. Refer to the Microsoft Security Update Guide for authoritative technical details.

Detection Methods for CVE-2026-69548

Indicators of Compromise

Unexpected USB device enumeration events referencing RNDIS class descriptors on endpoints without a business need for USB tethering.
Windows event log entries showing repeated RNDIS driver loads or driver crashes tied to newly connected removable hardware.
Kernel-mode faults or bugchecks in usb8023.sys or rndismp.sys shortly after device insertion.

Detection Strategies

Correlate USB device insertion telemetry with driver load events to identify anomalous RNDIS adapter attachments.
Alert on any RNDIS network interface appearing on workstations that historically do not use USB networking.
Baseline authorized USB device VID/PID pairs and flag deviations, especially devices advertising the RNDIS communication class.

Monitoring Recommendations

Forward Windows Microsoft-Windows-DriverFrameworks-UserMode and Kernel-PnP event channels to a central log platform for review.
Monitor for repeated short-duration RNDIS device attach and detach cycles that may indicate probing.
Track physical access events at high-value endpoints and correlate with hardware enumeration logs.

How to Mitigate CVE-2026-69548

Immediate Actions Required

Apply the security update referenced in the Microsoft Security Update Guide to all affected Windows systems.
Prioritize patching for laptops, kiosks, and shared workstations where physical access by untrusted parties is possible.
Audit endpoints for unauthorized USB devices and remove any unapproved RNDIS-capable hardware.

Patch Information

Microsoft has published a security update addressing the RNDIS heap overflow. Consult the Microsoft Security Update Guide entry for CVE-2026-69548 for the specific KB numbers, affected Windows builds, and installation guidance.

Workarounds

Enforce USB device control policies to block unapproved network-class devices at the operating system level.
Disable or restrict loading of the RNDIS driver on systems that do not require USB tethering functionality.
Apply physical security controls such as port blockers and locked enclosures for endpoints in exposed environments.

bash

# Configuration example: block RNDIS device class via Group Policy
# Computer Configuration > Administrative Templates > System > Device Installation > Device Installation Restrictions
# Prevent installation of devices matching the following device setup class:
# {ad498944-762f-11d0-8dcb-00c04fc3358c}  (Net)
# Combined with device instance ID filters for RNDIS-specific hardware IDs, e.g. USB\Class_02&SubClass_02