Windows Heap Buffer Overflow Vulnerability Allows Attackers to Gain Elevated Privileges

Cybersecurity

A critical security vulnerability has been identified in Microsoft Windows systems, enabling attackers to elevate privileges and potentially gain control over affected machines.

Product Update

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

Vulnerability Overview

This security flaw is a heap-based buffer overflow located in the ksthunk.sys driver, particularly within the CKSAutomationThunk::HandleArrayProperty() function. It allows authorized users with low-level privileges to escalate their access to system-level permissions, compromising the Windows installation.

• CVE ID: CVE-2025-53149
• Vulnerability Type: Heap-based Buffer Overflow
• Component: Kernel Streaming WOW Thunk Service Driver (ksthunk.sys)
• CVSS Score: 7.8 (High)

The vulnerability was discovered by security researchers at Crowdfense during their analysis of Windows internals. The affected component, ksthunk.sys, acts as a bridge between 32-bit user applications and 64-bit kernel drivers, making it a target for privilege escalation.

Technical Details

The vulnerability exists within the Kernel Streaming WOW Thunk Service Driver, responsible for handling multimedia streaming operations on 64-bit Windows systems. It serves as a “thunk” layer, translating requests between system environments, specifically 32-bit user-mode applications and 64-bit kernel-mode drivers.

The flaw is triggered when processing KSPROPERTY_VPCONFIG_DDRAWSURFACEHANDLE requests through the vulnerable function, where the driver fails to validate output buffer lengths, leading to a heap overflow condition exploitable by malicious code.

The vulnerable driver is identified by the SHA-1 hash 68B5B527550731DD657BF8F1E8FA31E895A7F176. Successful exploitation allows attackers to manipulate memory allocation and data processes to execute arbitrary code with elevated privileges.

The vulnerability was responsibly disclosed, initially discovered on Fri, Apr 14, 2025, and reported to Microsoft on Tue, Apr 18, 2025. Microsoft confirmed the issue on Tue, May 20, 2025, and awarded a security bounty on Wed, Jun 4, 2025.

Mitigation and Protection

Microsoft has issued security updates addressing this vulnerability as part of the August 2025 Patch Tuesday release. System administrators and users should apply these patches immediately to safeguard systems from potential exploitation.

The patch resolves the issue by implementing proper validation checks for output buffer lengths in the vulnerable function, preventing the heap overflow condition that enabled privilege escalation attacks.

Although no active exploitation has been reported, the public release of technical details increases the risk of future attacks. Security teams should ensure Windows systems are updated and monitor for suspicious privilege escalation activities.

The discovery of CVE-2025-53149 underscores the critical role of security research in identifying and addressing vulnerabilities in essential system components, including less obvious drivers like the Kernel Streaming WOW Thunk Service Driver.