A critical vulnerability has been discovered in the Windows Desktop Window Manager (DWM) that could allow attackers to escalate privileges to system level.
The flaw, tracked as CVE-2025-55681, resides in the dwmcore.dll component and was disclosed during the TyphoonPWN Windows security competition, where it earned second place recognition.
The Vulnerability
The vulnerability exists within the CBrushRenderingGraphBuilder::AddEffectBrush function in the DWM core library.
The flaw stems from improper memory handling in the composition effect processing pipeline.
Specifically, attackers can manipulate user-controlled data in shared memory sections to create an out-of-bounds memory access condition.
By crafting malicious effect descriptions, an attacker can force the vulnerable code to read memory outside allocated boundaries and use this data for subsequent operations.
The technical root cause involves the deserialization of effect graph structures without proper bounds validation.
When the DeserializeEffectDescription function processes user-supplied data, it fails to verify index values used in array access operations.
This allows an attacker to control critical indices that later determine memory access patterns, leading to arbitrary out-of-bounds reads.
According to SSD Disclosure, the exploitation chain begins with manipulating the CCompiledEffect object initialization.
By setting specific reference properties on an CEffectBrush object through composition APIs, an attacker can inject a malicious CompiledEffect containing crafted effect description data.
The vulnerable code path chains multiple function calls including CVisual::ProcessSetWindowBackgroundTreatment, CWindowBackgroundTreatment::Create, and ultimately CBrushRenderingGraphBuilder::AddEffectBrushwhere 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 can 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.
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. Organizations and individual users should immediately apply the available security update from the Microsoft Security Response Center at the provided vendor link.
The patch has been validated on Windows 11. Note that reliability on Windows 10 is reduced due to different heap management implementations.
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