Microsoft Desktop Window Manager Flaw Allows Privilege Escalation

A critical vulnerability has been identified in the Windows Desktop Window Manager (DWM), potentially allowing attackers to escalate privileges to the system level.

The flaw, designated as CVE-2025-55681, is located in the dwmcore.dll component. It was disclosed during the TyphoonPWN Windows security competition, where it received second place recognition.

The vulnerability is found in the CBrushRenderingGraphBuilder::AddEffectBrush function within the DWM core library. It arises from improper memory handling in the composition effect processing pipeline. Specifically, user-controlled data in shared memory sections can be manipulated to create an out-of-bounds memory access condition. Through malicious effect descriptions, attackers can force the vulnerable code to read memory outside allocated boundaries and use this data for subsequent operations.

The root cause involves the deserialization of effect graph structures without proper bounds validation. The DeserializeEffectDescription function processes user-supplied data without verifying index values used in array access operations, allowing attackers to control critical indices that dictate memory access patterns, leading to arbitrary out-of-bounds reads.

Exploitation begins with manipulating the CCompiledEffect object initialization. By setting specific reference properties on a CEffectBrush object through composition APIs, attackers can inject a malicious CompiledEffect containing crafted effect description data. The vulnerable code path involves multiple function calls, including CVisual::ProcessSetWindowBackgroundTreatment , CWindowBackgroundTreatment::Create , and CBrushRenderingGraphBuilder::AddEffectBrush , where the out-of-bounds condition is triggered.

Successful exploitation leverages Windows 11's Segment Heap memory manager. Attackers use precision heap spraying to place controllable data adjacent to vulnerable structures. By strategically freeing heap chunks, they 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.

Triggering the out-of-bounds condition and executing shellcode. Hooking MapViewOfFile to manipulate shared memory and escalate privileges via the User Account Control process. Executing privileged payloads by loading arbitrary DLLs in the elevated consent.exe context.

Microsoft has released patches to address this vulnerability. It is recommended that organizations and individual users apply the available security update from the Microsoft Security Response Center. The patch has been validated on Windows 11; however, reliability on Windows 10 is reduced due to different heap management implementations.

Based on reporting by GBHackers.