Windows Heap Buffer Overflow Vulnerability Allows Attackers to Gain Elevated Privileges

A critical security vulnerability has been discovered in Microsoft Windows systems that allows attackers to escalate their privileges and potentially gain complete control over affected machines.

The vulnerability, designated CVE-2025-53149, affects the Kernel Streaming WOW Thunk Service Driver and was patched by Microsoft in August 2025.

Vulnerability Overview

The security flaw is a heap-based buffer overflow located in the ksthunk.sys driver, specifically within the CKSAutomationThunk::HandleArrayProperty() function.

This vulnerability allows authorized users with low-level privileges to escalate their access to system-level permissions, potentially compromising the entire Windows installation.

Security researchers from Crowdfense discovered the vulnerability during their routine analysis of Windows internals.

The affected component, ksthunk.sys, serves as a critical bridge between 32-bit user applications and 64-bit kernel drivers in Windows systems, making it particularly valuable for attackers seeking privilege escalation.

Technical Details

The vulnerability exists in the Kernel Streaming WOW Thunk Service Driver, which handles multimedia streaming operations on 64-bit Windows systems.

The driver acts as a “thunk” layer that translates requests between different system environments, specifically bridging 32-bit user-mode applications with 64-bit kernel-mode drivers.

The security flaw occurs when the system processes KSPROPERTY_VPCONFIG_DDRAWSURFACEHANDLE requests through the vulnerable function.

 During this process, the driver fails to properly validate output buffer lengths, leading to a heap overflow condition that can be exploited by malicious code.

The vulnerable driver has been identified with SHA-1 hash 68B5B527550731DD657BF8F1E8FA31E895A7F176.

When exploited successfully, attackers can manipulate memory allocation and data copying processes to execute arbitrary code with elevated privileges.

The vulnerability followed a responsible disclosure process spanning several months. Security researchers initially discovered the flaw on April 14, 2025, and reported it to Microsoft four days later on April 18, 2025.

Microsoft confirmed the vulnerability on May 20, 2025, and awarded a security bounty on June 4, 2025.

Mitigation and Protection

Microsoft has released security updates addressing this vulnerability as part of their August 2025 Patch Tuesday release cycle.

System administrators and users should immediately apply the relevant security patches to protect their systems from potential exploitation.

The patch addresses the core issue by adding proper validation checks for output buffer lengths in the vulnerable function. This prevents the heap overflow condition that enabled privilege escalation attacks.

While no active exploitation has been reported in the wild, the technical details of the vulnerability have been made public, increasing the potential for future attack attempts.

Security teams should ensure their Windows systems are updated and monitor for any suspicious privilege escalation activities that might indicate exploitation attempts.

The discovery of CVE-2025-53149 highlights the ongoing importance of security research in identifying and addressing vulnerabilities in critical system components, even in seemingly obscure drivers like the Kernel Streaming WOW Thunk Service Driver.

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