CVE-2026-50409 Overview
CVE-2026-50409 is an information disclosure vulnerability in the Windows Overlay Filter (WOF) driver. The flaw exposes sensitive information to an unauthorized actor, allowing an authenticated local attacker to read data that should remain protected. Microsoft classifies the issue under [CWE-200] (Exposure of Sensitive Information to an Unauthorized Actor). The vulnerability affects a broad range of Windows client and server releases, including Windows 10, Windows 11, and Windows Server 2016 through 2025. Exploitation requires local access and low privileges but no user interaction.
Critical Impact
An authenticated local attacker can disclose sensitive in-memory or filesystem-related data handled by the Windows Overlay Filter, which may aid follow-on privilege escalation or lateral movement.
Affected Products
- Microsoft Windows 10 (1607, 1809, 21H2, 22H2)
- Microsoft Windows 11 (24H2, 25H2, 26H1)
- Microsoft Windows Server 2016, 2019, 2022, and 2025
Discovery Timeline
- 2026-07-14 - CVE-2026-50409 published to NVD
- 2026-07-20 - Last updated in NVD database
Technical Details for CVE-2026-50409
Vulnerability Analysis
The Windows Overlay Filter (WOF) is a kernel-mode file system filter driver used to transparently present compressed or backed-up file content to user-mode applications. It is heavily used by features such as Compact OS and Windows container images. CVE-2026-50409 stems from improper handling of internal data structures within WOF, resulting in unintended exposure of sensitive information to a caller that should not have access.
An attacker with valid local credentials can trigger the flaw through normal user-mode interfaces that reach the WOF driver. Because the confidentiality impact is high while integrity and availability are unaffected, the vulnerability aligns with a pure disclosure primitive rather than tampering or denial of service. Disclosed content may include kernel memory fragments, cached file metadata, or other data useful for chaining into privilege escalation.
Root Cause
The root cause is improper access enforcement or insufficient initialization within the Windows Overlay Filter driver code path. Under specific conditions, the driver returns memory contents that were never intended to cross the trust boundary between the kernel and a low-privileged local process. Microsoft has not publicly disclosed the exact code path. See the Microsoft CVE-2026-50409 Advisory for vendor guidance.
Attack Vector
Exploitation requires local access to the target system and any authenticated user context. The attacker interacts with the WOF driver through standard file system APIs or IOCTL requests, causing the driver to return sensitive data. No user interaction from a victim is required, and the attack does not cross a network boundary. Public proof-of-concept code is not currently available, and the EPSS score of 0.362% reflects a low near-term exploitation probability.
Detection Methods for CVE-2026-50409
Indicators of Compromise
- Unexpected local processes issuing high volumes of DeviceIoControl calls to WOF-related device objects such as \Device\Wof.
- Unsigned or newly introduced binaries in user-writable directories that enumerate or interact with Windows Overlay Filter interfaces.
- Local user accounts producing anomalous kernel driver interaction patterns outside of normal administrative activity.
Detection Strategies
- Monitor kernel driver interaction telemetry for non-administrative processes accessing file system filter drivers.
- Correlate suspicious local process behavior with subsequent privilege escalation attempts or credential access activity.
- Baseline legitimate WOF usage on servers and workstations to identify deviations that may indicate exploitation attempts.
Monitoring Recommendations
- Enable Windows Defender Application Control and audit-mode logging to capture unusual binaries interacting with kernel components.
- Ingest Windows Security and Sysmon events into a centralized SIEM to review Process Create and Image Load events for suspicious executables.
- Alert on repeated failed access attempts or high-frequency IOCTL activity targeting file system filter drivers.
How to Mitigate CVE-2026-50409
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft CVE-2026-50409 Advisory to all affected Windows and Windows Server systems.
- Prioritize patching multi-user systems such as Remote Desktop Session Hosts, Citrix servers, and shared workstations where local attackers are more likely.
- Restrict local logon rights on sensitive servers to the minimum set of administrators required for operations.
Patch Information
Microsoft has released a security update through the Microsoft Update Guide. Administrators should deploy the update via Windows Update, Windows Server Update Services (WSUS), Microsoft Intune, or Configuration Manager. Refer to the vendor advisory for build-specific KB article numbers.
Workarounds
- No official workaround has been published by Microsoft; patching remains the primary remediation.
- Reduce exposure by limiting interactive and remote local logon rights to trusted users only.
- Enforce application allowlisting to block unauthorized binaries that could probe the Windows Overlay Filter driver.
# Verify installed updates on a Windows host
wmic qfe list brief /format:table
# Trigger update scan via PowerShell
UsoClient StartScan
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
