Microsoft Desktop Window Manager Flaw Allows Privilege Escalation

A critical vulnerability has been identified in the Windows Desktop Window Manager (DWM) that could potentially allow attackers to escalate privileges to system level, posing a significant threat to Windows users.

The vulnerability, tracked as CVE-2025-55681, is located in the dwmcore.dll component and was recently disclosed during the TyphoonPWN Windows security competition, where it received second-place recognition for its severity.

Understanding the Vulnerability

The vulnerability exists within the CBrushRenderingGraphBuilder::AddEffectBrush function in the DWM core library, which is responsible for managing graphical effects on the Windows desktop.

The flaw is caused by improper memory handling in the composition effect processing pipeline, allowing attackers to manipulate user-controlled data in shared memory sections and create an out-of-bounds memory access condition.

Specifically, attackers can craft malicious effect descriptions to force the vulnerable code to read memory outside allocated boundaries and use this data for subsequent operations, potentially leading to arbitrary code execution.

The technical root cause of the vulnerability involves the deserialization of effect graph structures without proper bounds validation, which allows an attacker to control critical indices that determine memory access patterns.

When the DeserializeEffectDescription function processes user-supplied data, it fails to verify index values used in array access operations, enabling an attacker to control critical indices and leading to arbitrary out-of-bounds reads.

According to SSD Disclosure, the exploitation chain begins with manipulating the CCompiledEffect object initialization, allowing an attacker to inject a malicious CompiledEffect containing crafted effect description data.

By setting specific reference properties on an CEffectBrush object through composition APIs, an attacker can trigger the vulnerable code path, which chains multiple function calls, including CVisual::ProcessSetWindowBackgroundTreatment, CWindowBackgroundTreatment::Create, and ultimately CBrushRenderingGraphBuilder::AddEffectBrush, where the out-of-bounds condition is triggered.

Successful exploitation leverages Windows 11’s Segment Heap memory manager, allowing attackers to use precision heap spraying to place controllable data adjacent to vulnerable structures and manipulate the Red-Black tree structure that manages free memory, enabling pointer leaks.

These pointers facilitate indirect function calls through crafted virtual method tables, ultimately loading arbitrary code into memory and allowing attackers to escalate privileges.

The attack progresses through three stages: first, triggering the out-of-bounds condition and executing shellcode; second, hooking MapViewOfFile to manipulate shared memory and escalate privileges through the User Account Control process; and finally, executing privileged payloads by loading arbitrary DLLs in the elevated consent.exe context.

Microsoft has released patches addressing this vulnerability, and organizations and individual users are advised to immediately apply the available security update from the Microsoft Security Response Center.

The patch has been validated on Windows 11, although reliability on Windows 10 is reduced due to different heap management implementations.