Windows MBT Transport Driver Integer Underflow (CVE-2025-47996): A Privilege Escalation Risk You Can't Ignore

Introduction

In July 2025, Microsoft disclosed a critical integer underflow vulnerability (CVE-2025-47996) in the Windows MBT Transport Driver (netbt.sys), a kernel-level component essential for legacy NetBIOS communications. This flaw represents a significant risk, enabling local attackers with minimal privileges to escalate their access to SYSTEM-level control, potentially compromising entire systems and networks.

Technical Information

The vulnerability arises from improper handling of integer arithmetic within the MBT Transport Driver. Specifically, an integer underflow occurs when a subtraction operation results in a value below the minimum allowable integer, causing a wrap-around to a large positive number. This miscalculation leads to insufficient buffer allocation, creating conditions ripe for memory corruption.

Attackers exploiting this flaw can craft specific inputs that trigger the underflow, causing the driver to allocate smaller-than-required buffers. Subsequent operations overflow these buffers, overwriting adjacent kernel memory structures. This can corrupt critical kernel objects, such as function pointers or security tokens, enabling attackers to escalate privileges from standard user to SYSTEM-level.

The MBT Transport Driver (netbt.sys) is a critical kernel-mode driver facilitating NetBIOS over TCP/IP, a legacy protocol still widely used in enterprise environments for compatibility with older applications and network services.

Patch Information

Microsoft has addressed the integer underflow vulnerability in the Windows MBT Transport driver (CVE-2025-47996) by releasing a security update. This update modifies the driver's code to include additional boundary checks, ensuring that integer values are properly validated before any arithmetic operations are performed. By implementing these checks, the update prevents the occurrence of integer underflow conditions that could lead to privilege escalation.

To apply this security update, users should follow these steps:

Access the Microsoft Security Update Guide: Navigate to the official Microsoft Security Update Guide page for CVE-2025-47996.
Review the Update Details: On the page, you'll find comprehensive information about the vulnerability, including affected systems and the specific updates available.
Download the Appropriate Update: Identify the update that corresponds to your system's version and architecture. Click on the provided link to download the update package.
Install the Update: Once downloaded, run the installer and follow the on-screen instructions to complete the installation process.
Restart Your System: After installation, it's recommended to restart your computer to ensure that the update is fully applied.

By promptly applying this update, users can mitigate the risk associated with this vulnerability and enhance the security of their systems.

Affected Systems and Versions

Currently, specific affected versions have not been detailed publicly. Users should consult the official Microsoft Security Update Guide for precise version information relevant to their systems.

References

Source: This report was created using AI

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