CVE-2026-48566: Windows 11 24h2 Information Disclosure

CVE-2026-48566 Overview

CVE-2026-48566 is an out-of-bounds read vulnerability [CWE-125] in the Windows Desktop Window Manager (DWM) Core Library. An authorized local attacker can exploit the flaw to read memory contents outside the intended buffer boundaries, resulting in information disclosure. The vulnerability affects multiple Windows 11 releases and Windows Server 2025.

The issue requires local access and low-level privileges, with no user interaction. Successful exploitation discloses sensitive in-process memory but does not impact integrity or availability. Microsoft published the advisory on June 9, 2026, and assigned a CVSS 3.1 base score of 5.5.

Critical Impact

Authorized local attackers can read out-of-bounds memory from the DWM Core Library, exposing potentially sensitive process data on affected Windows 11 and Windows Server 2025 systems.

Affected Products

• Microsoft Windows 11 24H2 (x64, ARM64)
• Microsoft Windows 11 25H2 (x64, ARM64)
• Microsoft Windows 11 26H1 (x64, ARM64)
• Microsoft Windows Server 2025 (x64)

Discovery Timeline

• 2026-06-09 - CVE-2026-48566 published to NVD
• 2026-06-10 - Last updated in NVD database

Technical Details for CVE-2026-48566

Vulnerability Analysis

The Desktop Window Manager (DWM) Core Library handles composition, rendering, and visual effects for the Windows graphical subsystem. The component runs with elevated privileges and processes graphical data structures from user-mode callers. An out-of-bounds read occurs when the library reads beyond the allocated boundaries of a buffer during processing.

The flaw produces a confidentiality impact without affecting integrity or availability. Returned data may contain heap contents, pointers, or other process state useful for bypassing exploit mitigations such as Address Space Layout Randomization (ASLR). Attackers commonly chain information disclosure primitives with separate memory corruption flaws to achieve code execution.

Root Cause

The vulnerability stems from improper validation of buffer boundaries during a read operation within dwmcore.dll. The component fails to verify that an index, offset, or size value remains within the bounds of the source buffer before dereferencing memory, classified under [CWE-125] Out-of-bounds Read. Microsoft has not released technical specifics on the affected code path.

Attack Vector

Exploitation requires local access with low privileges on the target system. The attacker executes code that interacts with DWM through legitimate graphical interfaces or interprocess communication channels. No user interaction is required. The attack does not cross security boundaries by itself but can supply leaked memory addresses to subsequent stages of an exploit chain.

No proof-of-concept code is publicly available, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. The EPSS score is 0.051% at the 16.3 percentile, indicating a low probability of near-term exploitation. Technical details are limited to the Microsoft CVE-2026-48566 Advisory.

Detection Methods for CVE-2026-48566

Indicators of Compromise

• Unexpected child processes spawned by dwm.exe or processes injecting into the DWM session
• Anomalous memory access patterns or crashes referencing dwmcore.dll
• Local user processes making unusual DWM API calls or composition requests outside normal application behavior
• Presence of unsigned or unknown binaries on endpoints lacking the June 2026 cumulative update

Detection Strategies

• Monitor Windows Event Logs for application crashes citing dwmcore.dll or dwm.exe faulting modules
• Apply endpoint detection rules that flag local processes attempting to read or inject into DWM memory space
• Audit installed update history to identify endpoints missing the relevant Microsoft security patch
• Correlate local privilege escalation indicators with information disclosure attempts in behavioral telemetry

Monitoring Recommendations

• Track patch compliance across all Windows 11 24H2, 25H2, 26H1, and Server 2025 systems
• Enable Microsoft Defender or equivalent EDR exploit guard policies for graphics subsystem processes
• Collect process creation, image load, and memory access telemetry centrally for retrospective hunting
• Review local logon and session activity for unexpected interactive use on servers

How to Mitigate CVE-2026-48566

Immediate Actions Required

• Apply the Microsoft security update referenced in the Microsoft CVE-2026-48566 Advisory to all affected systems
• Prioritize patching of multi-user systems, jump hosts, and Remote Desktop Session Hosts where local access is broadly available
• Restrict interactive logon rights on Windows Server 2025 deployments to required administrators only
• Verify that endpoint protection signatures and behavioral rules are updated

Patch Information

Microsoft has released security updates addressing CVE-2026-48566 for Windows 11 24H2, 25H2, 26H1, and Windows Server 2025 across x64 and ARM64 architectures. Administrators should consult the Microsoft CVE-2026-48566 Advisory for the specific knowledge base article numbers and deploy through Windows Update, WSUS, or Microsoft Intune.

Workarounds

• No official workaround has been published by Microsoft; patching is the recommended remediation
• Reduce attack surface by limiting which users can execute arbitrary code on affected endpoints
• Enforce least privilege and remove unnecessary local accounts on shared systems
• Apply application control policies such as Windows Defender Application Control (WDAC) to block unauthorized binaries

# Verify installed updates on an affected Windows host
wmic qfe list brief /format:table

# Force a Windows Update scan and install
UsoClient StartScan
UsoClient StartDownload
UsoClient StartInstall