CVE-2023-23376: Windows 10 1507 Privilege Escalation Flaw

CVE-2023-23376 Overview

CVE-2023-23376 is a critical elevation of privilege vulnerability in the Windows Common Log File System (CLFS) driver that affects a wide range of Microsoft Windows operating systems. This vulnerability allows an authenticated attacker with local access to escalate privileges from a standard user account to SYSTEM-level privileges, effectively gaining complete control over the affected system.

The Common Log File System is a general-purpose logging subsystem in Windows that can be used by both kernel-mode and user-mode applications. Due to the privileged nature of the CLFS driver operating at the kernel level, any vulnerability in this component presents significant security risks.

Critical Impact

This vulnerability is actively exploited in the wild and has been added to CISA's Known Exploited Vulnerabilities (KEV) catalog. Successful exploitation grants attackers SYSTEM-level privileges, enabling complete system compromise, lateral movement, and persistent access.

Affected Products

• Microsoft Windows 10 (versions 1507, 1607, 1809, 20H2, 21H2, 22H2)
• Microsoft Windows 11 (versions 21H2, 22H2)
• Microsoft Windows Server 2008 (SP2, R2 SP1)
• Microsoft Windows Server 2012 (including R2)
• Microsoft Windows Server 2016
• Microsoft Windows Server 2019
• Microsoft Windows Server 2022

Discovery Timeline

• 2023-02-14 - CVE-2023-23376 published to NVD
• 2025-10-27 - Last updated in NVD database

Technical Details for CVE-2023-23376

Vulnerability Analysis

This elevation of privilege vulnerability exists within the Windows Common Log File System driver (clfs.sys). The vulnerability is classified under CWE-122 (Heap-based Buffer Overflow) and CWE-787 (Out-of-bounds Write), indicating that the flaw involves improper bounds checking when processing CLFS log files.

The CLFS driver is responsible for managing log file operations at the kernel level. When processing specially crafted log file data, the driver fails to properly validate input boundaries, allowing an attacker to corrupt kernel memory. This memory corruption can be leveraged to overwrite critical kernel data structures, ultimately allowing arbitrary code execution with kernel privileges.

The attack requires local access and low privileges to initiate, but no user interaction is needed for successful exploitation. Once exploited, the attacker gains SYSTEM privileges, the highest privilege level on Windows systems.

Root Cause

The root cause of CVE-2023-23376 is a heap-based buffer overflow combined with an out-of-bounds write condition in the CLFS driver. The vulnerability stems from improper validation of data within CLFS log files (.blf files). When the driver parses malformed log file structures, it fails to adequately verify the size and bounds of data being processed, leading to memory corruption in the kernel heap.

This type of vulnerability is particularly dangerous because it occurs in a kernel-mode driver, meaning successful exploitation immediately grants the highest level of system access without requiring additional privilege escalation chains.

Attack Vector

The attack vector for this vulnerability is local, requiring an attacker to have already gained initial access to the target system with at least low-level privileges. The typical attack flow involves:

1. An attacker gains initial access to a Windows system through phishing, malware, or other means
2. The attacker creates a malicious CLFS log file (.blf) containing specially crafted data structures
3. The attacker triggers the CLFS driver to process the malicious log file
4. The vulnerable driver code performs an out-of-bounds write operation, corrupting kernel memory
5. The memory corruption is leveraged to execute arbitrary code with SYSTEM privileges

This vulnerability has been observed being used as part of attack chains where threat actors first establish a foothold on systems and then use CVE-2023-23376 to escalate privileges before deploying ransomware or conducting further malicious activities.

Detection Methods for CVE-2023-23376

Indicators of Compromise

• Suspicious creation or modification of .blf (Base Log File) files in unexpected directories
• Unusual process activity involving clfs.sys driver operations
• Evidence of privilege escalation from low-privileged accounts to SYSTEM
• Anomalous kernel memory access patterns or system crashes related to CLFS operations
• Creation of new administrator accounts or modification of existing account privileges following exploitation

Detection Strategies

• Monitor for suspicious file operations involving CLFS log files (.blf extension) in user-writable locations
• Implement kernel-level monitoring for anomalous CLFS driver behavior and heap memory allocation patterns
• Deploy endpoint detection and response (EDR) solutions capable of detecting privilege escalation attempts
• Use Windows Event Log analysis to identify sudden privilege changes or suspicious SYSTEM-level process creation
• Correlate process creation events with file system activity involving CLFS-related files

Monitoring Recommendations

• Enable advanced auditing for file system access, particularly for log file operations
• Configure SentinelOne Singularity to monitor for kernel exploitation attempts and privilege escalation behaviors
• Implement behavioral detection rules for suspicious sequences of low-privilege to high-privilege transitions
• Monitor for known exploit tools and frameworks that incorporate CVE-2023-23376 exploitation capabilities

How to Mitigate CVE-2023-23376

Immediate Actions Required

• Apply Microsoft's February 2023 security updates immediately across all affected Windows systems
• Prioritize patching for internet-facing systems and critical infrastructure
• Review systems for signs of compromise, as this vulnerability has been actively exploited in the wild
• Ensure SentinelOne agents are deployed and updated to detect exploitation attempts
• Limit local user privileges to reduce the attack surface for post-exploitation privilege escalation

Patch Information

Microsoft has released security updates addressing CVE-2023-23376 as part of the February 2023 Patch Tuesday release. Organizations should apply the appropriate updates for their Windows versions through Windows Update, Windows Server Update Services (WSUS), or the Microsoft Update Catalog.

For detailed patch information and download links, refer to the Microsoft Security Update Guide.

Due to the active exploitation of this vulnerability, CISA has mandated federal agencies to apply patches by a specified deadline. All organizations should treat this as a high-priority patching effort. Additional information is available from the CISA Known Exploited Vulnerabilities Catalog.

Workarounds

• Implement strict application control policies to prevent unauthorized executables from running
• Apply the principle of least privilege to minimize the number of users with local system access
• Segment critical systems and limit lateral movement capabilities within the network
• Deploy endpoint protection solutions with behavioral analysis to detect exploitation attempts
• Consider restricting access to the CLFS driver functionality through Group Policy for non-essential systems where feasible

# Verify Windows Update status and pending security updates
wmic qfe list brief | findstr /i "KB5022834 KB5022836 KB5022838"

# Check for signs of CLFS-related exploitation attempts in Security logs
wevtutil qe Security /q:"*[System[(EventID=4688)]]" /f:text | findstr /i "clfs"