CVE-2026-50697 Overview
CVE-2026-50697 is an information disclosure vulnerability in the Windows Common Log File System (CLFS) driver that allows an authorized local attacker to elevate privileges. The flaw exposes sensitive kernel information to an unauthorized actor [CWE-200], enabling attackers with low-privileged local access to obtain data useful for further exploitation. Microsoft published the advisory on July 14, 2026, covering supported Windows client and server SKUs. The vulnerability requires local access and low privileges, with no user interaction required. Successful exploitation results in high impact to confidentiality, integrity, and availability.
Critical Impact
An authenticated local attacker can leverage sensitive information leaked by the CLFS driver to elevate to SYSTEM privileges on affected Windows and Windows Server installations.
Affected Products
- Microsoft Windows 10 (1607, 1809, 21H2, 22H2)
- Microsoft Windows 11 (24H2, 25H2, 26H1)
- Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, and 2025
Discovery Timeline
- 2026-07-14 - CVE-2026-50697 published to NVD
- 2026-07-16 - Last updated in NVD database
Technical Details for CVE-2026-50697
Vulnerability Analysis
The Common Log File System (CLFS) driver (clfs.sys) is a general-purpose logging subsystem used by kernel-mode and user-mode components in Windows. CVE-2026-50697 stems from improper handling of sensitive kernel data within CLFS operations, exposing information to callers that should not have access to it. This class of driver flaw commonly leaks kernel memory addresses, pointers, or structure contents that defeat Kernel Address Space Layout Randomization (KASLR).
An authorized attacker with a low-privileged local account can invoke affected CLFS interfaces to retrieve leaked data. The leaked contents can then be chained with a separate memory corruption primitive to achieve reliable elevation of privilege to SYSTEM. The CVSS 3.1 score of 7.8 reflects high impact across confidentiality, integrity, and availability once the leak is weaponized.
Root Cause
The vulnerability is categorized as CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor). Microsoft's advisory attributes the issue to the CLFS driver returning or exposing kernel-mode data to lower-privileged callers without adequate sanitization or access checks. CLFS has historically been a frequent source of privilege escalation vulnerabilities due to its complex handling of base log files (BLFs) and log record structures.
Attack Vector
Exploitation requires local code execution as a standard user. The attacker interacts with CLFS through documented or undocumented APIs, triggers the vulnerable code path, and reads back the exposed kernel data. No user interaction is required, and the attack scope is unchanged. The EPSS score of 0.284% (20.45th percentile) indicates a low near-term probability of observed exploitation, though CLFS bugs are frequently weaponized post-disclosure.
Refer to the Microsoft Security Update Guide for CVE-2026-50697 for vendor technical details.
Detection Methods for CVE-2026-50697
Indicators of Compromise
- Unexpected creation or manipulation of CLFS base log files (.blf) or container files by non-administrative processes.
- Unusual user-mode processes issuing NtCreateFile or DeviceIoControl calls targeting \Device\CLFS.
- Standard user processes spawning SYSTEM-level child processes shortly after CLFS API activity.
Detection Strategies
- Monitor kernel driver telemetry for anomalous CLFS API invocations originating from low-privilege user contexts.
- Correlate process integrity level transitions from Medium to System with recent CLFS handle operations.
- Deploy behavioral analytics that flag token manipulation or process access patterns consistent with local privilege escalation chains.
Monitoring Recommendations
- Enable Windows Event Log auditing for driver load events and CLFS-related object access under Security event IDs 4656 and 4663.
- Ingest Sysmon Event ID 1 (process creation) and Event ID 10 (process access) into a SIEM to identify suspicious escalation sequences.
- Track file activity in %SystemRoot%\System32\config\ and user-writable directories where crafted BLF files may be staged.
How to Mitigate CVE-2026-50697
Immediate Actions Required
- Apply the Microsoft security update referenced in the MSRC advisory for CVE-2026-50697 to all affected Windows and Windows Server systems.
- Prioritize patching of multi-user systems, terminal servers, and endpoints accessible to standard users.
- Audit local account inventory and remove unnecessary interactive logon rights for non-administrative users.
Patch Information
Microsoft has released cumulative security updates addressing CVE-2026-50697 for all supported Windows 10, Windows 11, and Windows Server versions listed above. Consult the Microsoft Security Update Guide for the specific KB article and build numbers applicable to each operating system version.
Workarounds
- No official workaround has been published by Microsoft; patching is the required remediation path.
- Restrict local interactive and remote desktop logon to trusted administrators until patches are deployed.
- Apply application allowlisting to prevent execution of untrusted binaries that could invoke CLFS APIs.
# Verify patch deployment status via PowerShell
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 10
# Query Windows Update history for the CLFS-related KB
wmic qfe list brief /format:table
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
