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CVE-2026-50409 is an information disclosure vulnerability affecting the Windows Overlay Filter component—a kernel‑mode driver used by Unified Write Filter (UWF) and File‑Based Write Filter (FBWF) to redirect write operations to a temporary overlay cache. The flaw stems from improper handling of I/O requests that originate from user‑mode processes. When a local, authenticated attacker with low privileges sends a specially crafted request to the overlay filter, the driver fails to adequately sanitize or restrict the data returned in response. As a result, the driver inadvertently exposes kernel‑memory contents or sensitive internal state information that should remain inaccessible to non‑administrative users.
The vulnerability is classified under CWE‑200 (Exposure of Sensitive Information to an Unauthorized Actor). The attack requires local access and low privileges, meaning the attacker must already have a foothold on the system (e.g., as a standard user). No user interaction is needed, and the attack complexity is low. The confidentiality impact is rated High, while integrity and availability are unaffected. The CVSSv3.1 base score is 5.5 (MEDIUM) with the vector AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N. Microsoft assigned this CVE on June 4, 2026, and publicly disclosed it on July 14, 2026. At the time of writing, no public exploit or proof‑of‑concept code is available, and the vulnerability is not listed in CISA’s Known Exploited Vulnerabilities catalog.
The underlying issue arises from the Overlay Filter’s response logic when processing certain query operations. The driver does not validate the length or scope of the output buffer provided by the caller, leading to an excessive data output condition. This allows a local attacker to read kernel‑pool memory or other sensitive structures that reside in the same address space. Because the filter operates at the kernel level, any leakage can expose cryptographic keys, process tokens, or memory addresses that aid in further privilege‑escalation attacks. The vulnerability affects all modern Windows client and server versions, including Windows 10 (1607, 1809, 21H2, 22H2), Windows 11 (24H2, 25H2, 26H1), and Windows Server (2016, 2019, 2022, 2025). Although the EPSS score is below 1%, indicating low exploitability in the wild, the local nature of the attack and the potential for sensitive data exposure make it a priority for patch management.
DailyCVE Form:
Platform: Windows 10/11/Server
Version: 1607‑26H1/2016‑2025
Vulnerability: Information Disclosure (CWE‑200)
Severity: Medium (CVSS 5.5)
date: 2026‑07‑14
Prediction: 2026‑07‑21 (Patch Tuesday)
What Undercode Say:
Analytics (Threat Intelligence & Attack Surface)
- CTI Interest Score: 0.66 (low) – limited chatter in underground forums.
- Exploit Price Estimation: $5,000 – $25,000 (as of July 14, 2026).
- MITRE ATT&CK Technique: T1592 (Gather Victim Host Information).
- EPSS Probability: < 1% – low likelihood of exploitation in the next 30 days.
- CISA KEV: Not listed – no active exploitation observed.
- Affected Installations: Estimated millions of Windows endpoints worldwide.
Bash Commands & Detection Scripts
Check if the Overlay Filter driver is loaded sc query WofService | findstr "RUNNING" Enumerate all overlay volumes (requires admin) fsutil volume queryoverlay C: Monitor for suspicious I/O requests to the filter (using Sysmon) sysmon -accepteula -i -n Then look for events with ProcessGuid and Image containing "overlay" PowerShell snippet to check UWF status (if enabled) Get-WindowsOptionalFeature -Online -FeatureName "Client-EmbeddedShellLauncher" Query the Windows Filtering Platform for overlay‑related rules netsh wfp show filters | findstr "overlay"
Exploit:
To exploit CVE‑2026‑50409, an attacker with local, low‑privileged access crafts a malicious user‑mode application that invokes the `DeviceIoControl` API with a specific IOCTL code targeting the Overlay Filter driver (\\.\WOF). The IOCTL is designed to query the filter’s internal state, but due to insufficient output‑buffer validation, the driver returns more data than intended—including adjacent kernel memory. The attacker can repeatedly call this IOCTL with varying input parameters to gradually leak sensitive kernel structures, such as EPROCESS tokens, system‑call addresses, or cached credentials. Because no user interaction is required and the attack complexity is low, this flaw can be weaponized in combination with other local exploits to elevate privileges or bypass security boundaries. Currently, no public exploit code exists, but the simplicity of the manipulation makes it a candidate for rapid reverse‑engineering.
Protection:
- Apply Security Updates: Install the latest cumulative update from Microsoft once released (expected July 21, 2026). Check the Microsoft Security Update Guide for the specific KB .
- Disable Unnecessary Components: If the Overlay Filter (UWF/FBWF) is not required, disable it via
dism /online /disable-feature /featurename:Client-EmbeddedShellLauncher. - Restrict Local Access: Enforce least‑privilege principles; limit the number of users who can log on locally. Use Group Policy to restrict interactive logon to only trusted administrators.
- Enable Windows Defender Exploit Guard: Configure Exploit Protection to block low‑integrity processes from calling `DeviceIoControl` on kernel drivers.
- Monitor for Anomalies: Use Sysmon or Event Tracing for Windows (ETW) to log all `DeviceIoControl` calls and alert on suspicious patterns targeting
\\.\WOF.
Impact:
Successful exploitation of CVE‑2026‑50409 allows a local, authenticated attacker to read sensitive information from kernel memory, which may include:
– System secrets: Cryptographic keys, hashed passwords, and Kerberos tickets.
– Process metadata: EPROCESS structures, token privileges, and security descriptors.
– Memory addresses: Kernel base addresses and function pointers that can be used to bypass ASLR and craft privilege‑escalation exploits.
– User data: Contents of recently accessed files or clipboard data if cached in kernel pools.
While the vulnerability does not grant direct code execution or privilege elevation, the disclosed information significantly reduces the effort required to mount further attacks. In enterprise environments, this could lead to lateral movement, credential theft, or full system compromise if combined with other flaws. The confidentiality impact is rated High, making this a moderate‑risk issue that demands timely patching and proactive monitoring.
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Sources:
Reported By: nvd.nist.gov
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