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CVE-2026-65787 is a heap-based buffer overflow vulnerability discovered in the Microsoft Windows Desktop Window Manager (DWM) component. DWM is the core Windows composition engine responsible for rendering all visual desktop elements—windows, animations, transparency effects, and other graphical user interface components—into a single image sent to the display. The vulnerability exists due to a boundary error in how DWM handles specially crafted data passed to the application.
An authorized attacker with local access to the target system can exploit this memory corruption flaw by sending crafted ALPC (Advanced Local Procedure Call) requests to the DWM service. When DWM processes these malformed requests, it fails to properly validate input sizes before copying data into heap-allocated buffers. This triggers a heap-based buffer overflow, overwriting adjacent memory structures. The overflow allows the attacker to corrupt critical heap metadata or function pointers, ultimately enabling arbitrary code execution within the context of the DWM process—which runs with SYSTEM-level privileges.
The vulnerability is particularly dangerous because DWM operates with high integrity privileges on all modern Windows systems. A successful exploit allows a local user to escalate from a low-privileged account to full SYSTEM access, compromising the entire machine. The attack requires no user interaction and has a low complexity, making it an attractive vector for privilege escalation in multi-user environments or following initial access via other means.
Microsoft assigned this vulnerability a CVSS v3.1 base score of 7.8 (HIGH) with the vector string AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. The vulnerability affects multiple Windows versions including Windows 10 (1607, 1809, 21H2, 22H2), Windows 11 (23H2, 24H2, 25H2, 26H1), and corresponding Windows Server editions. The CVE was published on August 11, 2026, and is associated with CWE-122 (Heap-based Buffer Overflow).
DailyCVE Form:
Platform: Windows 10/11/Server
Version: 10.0.14393–10.0.28000
Vulnerability: Heap Buffer Overflow
Severity: 7.8 HIGH
date: 08/11/2026
Prediction: 08/11/2026 (Patch Tuesday)
What Undercode Say:
Analytics & Detection:
To identify whether a system is vulnerable to CVE-2026-65787, administrators should verify the installed Windows version and DWM component build numbers.
Check current Windows build version:
systeminfo | findstr /B "OS Name OS Version"
Verify DWM core library file version (dwmcore.dll):
wmic datafile where name="C:\Windows\System32\dwmcore.dll" get Version
Monitor for suspicious ALPC traffic to the DWM service using Windows Event Tracing:
logman create trace DWM_Monitor -p "Microsoft-Windows-DWM" 0xFFFFFFFF -o C:\Logs\dwm.etl -ets logman start DWM_Monitor -ets
Check for unexpected DWM crashes or error events in the System log:
Get-WinEvent -LogName System | Where-Object { $<em>.ProviderName -eq "Application Error" -and $</em>.Message -match "dwm.exe" }
Query the Microsoft Update Catalog for the specific patch addressing CVE-2026-65787:
Get-HotFix | Where-Object { $_.Description -match "Security Update" } | Sort-Object InstalledOn -Descending
Exploit: (Educational Purposes!)
The exploitation of CVE-2026-65787 follows a typical heap-based buffer overflow pattern within the DWM component:
1. Reconnaissance: The attacker identifies the target Windows version and DWM build to determine heap layout and offsets.
2. Crafted ALPC Message: The attacker constructs a malicious ALPC message containing oversized data that exceeds the expected buffer size when processed by the vulnerable DWM function.
3. Heap Spray: Prior to triggering the overflow, the attacker performs heap spraying to place attacker-controlled data (e.g., shellcode and ROP gadgets) at predictable heap addresses.
4. Trigger Overflow: The crafted ALPC request is sent to the DWM service, causing the vulnerable function to copy the oversized payload into a heap buffer, overflowing into adjacent memory.
5. Corrupt Metadata/Function Pointer: The overflow overwrites critical heap metadata (e.g., chunk headers) or a function pointer stored adjacent to the buffer.
6. Control Flow Hijack: When DWM subsequently calls the corrupted function pointer or allocates from the corrupted heap, execution flow is redirected to the attacker’s shellcode.
7. SYSTEM Privilege Escalation: The shellcode executes with DWM’s SYSTEM-level privileges, spawning a SYSTEM shell or installing persistent backdoor.
Protection:
- Apply the official Microsoft security update released on August 11, 2026 (Patch Tuesday) immediately.
- Restrict local access to the target system; only allow authenticated and trusted users.
- Enable Windows Defender Exploit Guard (WDEG) with heap protections such as Heap Isolation and Arbitrary Code Guard.
- Deploy Endpoint Detection and Response (EDR) solutions that monitor for anomalous ALPC calls to DWM.
- Use Windows Application Control (WDAC) to restrict execution of untrusted binaries.
- Regularly audit user accounts and remove unnecessary local privileges.
- Consider disabling DWM if the desktop environment does not require compositing (not recommended for end-user systems).
Impact:
- Confidentiality: Full compromise of all data accessible to the SYSTEM account, including sensitive user files, credentials, and system secrets.
- Integrity: Complete control over the operating system, allowing installation of malware, backdoors, rootkits, and unauthorized software.
- Availability: Potential system instability, crashes, or denial of service due to memory corruption.
- Lateral Movement: After achieving SYSTEM privileges on one machine, the attacker can pivot to other systems on the network using stolen credentials or tokens.
- Persistence: The attacker can establish persistent access mechanisms (scheduled tasks, services, registry modifications) that survive reboots.
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Sources:
Reported By: nvd.nist.gov
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