CVE-2023-36424: Windows 10 1507 Privilege Escalation Flaw

CVE-2023-36424 Overview

CVE-2023-36424 is an elevation of privilege vulnerability in the Windows Common Log File System (CLFS) driver. The flaw is rooted in an out-of-bounds read condition tracked as [CWE-125]. A local, authenticated attacker can exploit the driver to obtain SYSTEM-level privileges on affected Windows desktop and server platforms. Microsoft published the advisory on November 14, 2023, and CISA has added the issue to its Known Exploited Vulnerabilities catalog, indicating confirmed in-the-wild abuse. The vulnerability affects supported builds from Windows Server 2008 through Windows 11 23H2 and Windows Server 2022 23H2.

Critical Impact

A local attacker with low privileges can gain SYSTEM rights, granting full control over the host with no user interaction required.

Affected Products

• Microsoft Windows 10 (versions 1507, 1607, 1809, 21H2, 22H2)
• Microsoft Windows 11 (versions 21H2, 22H2, 23H2)
• Microsoft Windows Server 2008, 2012, 2012 R2, 2016, 2019, 2022, and 2022 23H2

Discovery Timeline

• 2023-11-14 - CVE-2023-36424 published to NVD and Microsoft releases security patch
• 2026-04-14 - Last updated in NVD database

Technical Details for CVE-2023-36424

Vulnerability Analysis

The Common Log File System driver (clfs.sys) is a kernel-mode component that provides high-performance, general-purpose logging services to user-mode applications and kernel drivers. The driver parses Base Log File (BLF) structures supplied through user-controlled APIs, making it a recurring target for local privilege escalation research.

CVE-2023-36424 is classified as an out-of-bounds read [CWE-125]. The driver reads data outside the bounds of an allocated buffer when processing a crafted log file or log control block. The improper read enables an attacker to disclose kernel memory contents or corrupt kernel state used in subsequent operations, ultimately allowing privilege escalation to SYSTEM.

Because the attack vector is local and the privileges required are low, the issue is well suited as a post-exploitation primitive following initial access through phishing, commodity malware, or browser exploitation.

Root Cause

The root cause is insufficient bounds validation on attacker-controlled fields within CLFS log structures. When the driver dereferences offsets or length values that exceed the allocated container, it reads memory beyond the intended region. This pattern is consistent with the broader history of CLFS parsing flaws disclosed throughout 2022 and 2023.

Attack Vector

Exploitation requires local code execution on the target system as a standard user. The attacker invokes CLFS APIs to load or manipulate a crafted log file, triggering the out-of-bounds read inside clfs.sys. Successful exploitation yields execution in kernel context, which is used to elevate the current process token to SYSTEM. No user interaction is required beyond the attacker's own process activity.

No public proof-of-concept code is referenced in the CVE record. Technical details should be sourced from the Microsoft CVE-2023-36424 Update and the CISA Known Exploited Vulnerabilities catalog entry.

Detection Methods for CVE-2023-36424

Indicators of Compromise

• Creation of unexpected .blf Base Log Files in user-writable directories, particularly outside standard application paths.
• New SYSTEM-level child processes spawned from medium-integrity parent processes such as explorer.exe or Office applications.
• Unexpected loads or handle opens against \Device\CLFS from non-standard user-mode processes.

Detection Strategies

• Monitor for token manipulation patterns where a low-privilege process suddenly executes children under the NT AUTHORITY\SYSTEM account.
• Hunt for processes opening write handles to crafted CLFS log files immediately followed by anomalous kernel-mode behavior or crashes referencing clfs.sys.
• Correlate Windows Error Reporting bugcheck data citing clfs.sys with recent process executions from the same user session.

Monitoring Recommendations

• Enable Sysmon process creation (Event ID 1) and image load (Event ID 7) logging with rules covering clfs.sys and token elevation behavior.
• Forward kernel crash and reliability telemetry to a centralized analytics platform for correlation across endpoints.
• Track patch deployment status for the November 2023 Microsoft security update across all Windows endpoints and servers.

How to Mitigate CVE-2023-36424

Immediate Actions Required

• Apply the November 14, 2023 Microsoft security updates that address CVE-2023-36424 across all supported Windows client and server SKUs.
• Prioritize patching on multi-user systems, terminal servers, and any host exposed to untrusted local code execution.
• Audit endpoints flagged by CISA KEV reporting and validate patch level using a software inventory or vulnerability scanner.

Patch Information

Microsoft addressed the vulnerability in the November 2023 cumulative updates. Refer to the Microsoft Security Response Center advisory for the specific KB numbers mapped to each Windows build. CISA federal civilian agencies are required to remediate per the Known Exploited Vulnerabilities catalog.

Workarounds

• No vendor-supplied workaround exists. Patching is the only supported remediation path.
• Enforce least privilege and application allow-listing to limit which binaries can invoke CLFS APIs on sensitive hosts.
• Restrict local logon rights on servers and enforce strong endpoint identification controls to reduce the post-exploitation value of local code execution.

# Verify the November 2023 cumulative update is installed (PowerShell)
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 10

# Confirm clfs.sys file version against the patched build documented in MSRC
Get-Item C:\Windows\System32\drivers\clfs.sys | Select-Object VersionInfo