CVE-2023-28252: Windows 10 Privilege Escalation Flaw

CVE-2023-28252 Overview

CVE-2023-28252 is an elevation of privilege vulnerability in the Windows Common Log File System (CLFS) driver (clfs.sys). The flaw enables a local authenticated attacker to execute code with SYSTEM privileges on affected Windows desktop and server versions. CISA added this vulnerability to its Known Exploited Vulnerabilities catalog, confirming active exploitation in the wild. Ransomware operators leveraged the bug shortly after disclosure to escalate privileges during intrusion chains. The vulnerability is classified under [CWE-122] Heap-based Buffer Overflow and [CWE-787] Out-of-bounds Write.

Critical Impact

Local attackers with low-privileged access can gain SYSTEM-level privileges on unpatched Windows systems, enabling full host compromise.

Affected Products

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

Discovery Timeline

• 2023-04-11 - CVE-2023-28252 published to NVD and addressed in Microsoft's April 2023 Patch Tuesday release
• 2025-10-28 - Last updated in NVD database

Technical Details for CVE-2023-28252

Vulnerability Analysis

The vulnerability resides in the Common Log File System driver, a kernel-mode component (clfs.sys) responsible for managing transactional log files used by applications and Windows services. The flaw is a heap-based buffer overflow combined with an out-of-bounds write condition triggered when the driver parses attacker-controlled Base Log File (BLF) structures. Exploitation allows a local attacker to corrupt kernel memory and achieve arbitrary code execution at the SYSTEM privilege level. The bug has been weaponized by the Nokoyawa ransomware operators and other threat actors as part of post-compromise tooling.

Root Cause

The CLFS driver fails to properly validate fields within the BLF metadata when processing log file operations. Specifically, attacker-controlled offsets and size fields in the log block structures are trusted without bounds checking, leading to out-of-bounds writes into adjacent kernel heap allocations. The condition is reachable from a low-privileged user context because CLFS exposes its functionality through standard system calls available to unprivileged processes.

Attack Vector

Exploitation requires local access and the ability to execute code on the target system, typically following initial access through phishing, malware delivery, or another foothold. The attacker crafts a malicious BLF file and invokes CLFS APIs to trigger the corrupted parsing path. Successful exploitation pivots a standard user token to a SYSTEM token, enabling installation of drivers, credential theft, and disabling of security tooling.

No verified proof-of-concept code is reproduced here. Technical write-ups describing the exploitation primitive are available through the Packet Storm Exploit Report.

Detection Methods for CVE-2023-28252

Indicators of Compromise

• Creation of unexpected .blf files in user-writable directories outside standard application paths
• Unsigned or unusual processes invoking CLFS APIs followed by token elevation events
• Child processes of low-privileged applications spawning under the SYSTEM account
• Presence of Nokoyawa ransomware artifacts or known exploit binaries flagged by threat intelligence feeds

Detection Strategies

• Monitor for kernel pool corruption indicators and unexpected bug checks involving clfs.sys
• Flag process token changes where a non-elevated parent suddenly executes as SYSTEM without a legitimate elevation prompt
• Hunt for sequential CLFS log file operations originating from unexpected processes such as Office, browsers, or scripting engines
• Correlate suspicious .blf file writes with subsequent privilege escalation behaviors using behavioral analytics

Monitoring Recommendations

• Enable Windows kernel-mode driver auditing and forward Sysmon process creation and image load events to a centralized SIEM
• Track exploitation attempts using Microsoft Defender or third-party EDR signatures referencing CVE-2023-28252
• Review CISA KEV catalog entries and cross-reference internal patch compliance reporting

How to Mitigate CVE-2023-28252

Immediate Actions Required

• Apply the April 2023 Microsoft security updates to all affected Windows desktop and server systems
• Prioritize patching internet-facing servers and endpoints used by privileged users
• Audit endpoints for signs of prior exploitation, including unauthorized SYSTEM-level processes and persistence artifacts
• Restrict local logon rights on critical systems to reduce the pool of accounts able to trigger the flaw

Patch Information

Microsoft released cumulative security updates addressing CVE-2023-28252 on April 11, 2023, as part of Patch Tuesday. Refer to the Microsoft Security Update Guide for CVE-2023-28252 for the specific KB articles applicable to each Windows version. Apply the corresponding cumulative update for your Windows build to remediate the vulnerability.

Workarounds

• No vendor-supplied workarounds exist; patching is the only supported remediation
• Limit code execution on endpoints through application allowlisting (Windows Defender Application Control or AppLocker) to reduce exploit delivery opportunities
• Enforce least-privilege policies so that initial-access compromises do not immediately translate into local code execution

# Verify the April 2023 cumulative update is installed (PowerShell)
Get-HotFix | Where-Object { $_.InstalledOn -ge (Get-Date '2023-04-11') } | Sort-Object InstalledOn -Descending