CVE-2025-21367 Overview
CVE-2025-21367 is an elevation of privilege vulnerability in the Windows Win32 Kernel Subsystem. Microsoft disclosed the flaw as part of its February 2025 security release. The vulnerability is a use-after-free condition [CWE-416] in kernel-mode code that a locally authenticated attacker can trigger to gain SYSTEM privileges.
The issue affects a broad range of supported Windows client and server releases, including Windows 10, Windows 11, and Windows Server 2019 through Windows Server 2025. Exploitation requires local access and low privileges, with no user interaction.
Critical Impact
Successful exploitation grants an attacker SYSTEM-level privileges on the affected host, enabling full compromise of confidentiality, integrity, and availability.
Affected Products
- Microsoft Windows 10 (1809, 21H2, 22H2)
- Microsoft Windows 11 (22H2, 23H2, 24H2)
- Microsoft Windows Server 2019, 2022, 2022 23H2, and 2025
Discovery Timeline
- 2025-02-11 - CVE-2025-21367 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-21367
Vulnerability Analysis
The vulnerability resides in the Win32 Kernel Subsystem, the component that services user-mode window management and graphics calls in the Windows kernel. It is classified as a use-after-free flaw [CWE-416], where kernel code continues to reference an object after the memory backing it has been freed.
An attacker with an authenticated local session can invoke the vulnerable code path from user mode. Successful exploitation results in arbitrary code execution in kernel context, allowing the attacker to escalate from a standard user account to SYSTEM. This class of flaw is routinely combined with initial-access techniques such as phishing payloads or browser exploits to achieve full endpoint compromise.
Root Cause
The root cause is improper object lifetime management inside the Win32k kernel subsystem. A kernel object is dereferenced or reused after it has been released, allowing an attacker who can influence the freed allocation to control kernel memory. Microsoft has not published low-level technical details beyond identifying the component and the vulnerability class.
Attack Vector
The attack vector is local. An attacker must first obtain the ability to run code on the target as an authenticated user, typically through malware execution, a foothold from another exploit, or interactive access. From there, the attacker triggers the vulnerable Win32k syscall path to corrupt kernel memory and hijack execution flow.
No public proof-of-concept exploit is listed in the enriched data, and the vulnerability is not currently tracked in the CISA Known Exploited Vulnerabilities catalog.
See the Microsoft CVE-2025-21367 Advisory for vendor guidance.
Detection Methods for CVE-2025-21367
Indicators of Compromise
- Unexpected processes spawning child processes as NT AUTHORITY\SYSTEM from a non-elevated parent session.
- Kernel crashes or bug checks (for example 0x3B SYSTEM_SERVICE_EXCEPTION or 0x50 PAGE_FAULT_IN_NONPAGED_AREA) referencing win32k.sys or win32kfull.sys.
- New services, scheduled tasks, or drivers installed shortly after a standard user process performs unusual Win32k syscalls.
Detection Strategies
- Hunt for token manipulation and privilege escalation patterns where a user-context process suddenly runs with SYSTEM integrity.
- Correlate Windows Event ID 4672 (special privileges assigned) with process ancestry originating from non-administrative users.
- Monitor for loading of unsigned or newly written drivers following anomalous user activity.
Monitoring Recommendations
- Ensure endpoint telemetry captures kernel driver load events, process creation with full command lines, and integrity-level changes.
- Baseline normal Win32k syscall usage per application and alert on outliers from low-privilege processes.
- Forward Windows kernel error reports and Sysmon Event ID 1 and 10 data to a centralized SIEM for retrospective hunting.
How to Mitigate CVE-2025-21367
Immediate Actions Required
- Apply the February 2025 Microsoft security updates to all affected Windows client and server systems.
- Prioritize patching of multi-user hosts, terminal servers, and jump boxes where local accounts are most exposed.
- Restrict local logon rights and remove unnecessary standard user accounts from sensitive systems.
- Audit endpoints for existing signs of privilege escalation before and after patch deployment.
Patch Information
Microsoft has released security updates addressing CVE-2025-21367 across all supported affected products. Refer to the Microsoft CVE-2025-21367 Advisory for the specific KB articles and cumulative updates that correspond to each Windows build.
Workarounds
- No official workaround is published by Microsoft; applying the security update is the supported remediation.
- Reduce exposure by enforcing the principle of least privilege and preventing execution of untrusted binaries on endpoints.
- Enable attack surface reduction rules and application control policies such as Windows Defender Application Control to limit adversary ability to run exploit payloads.
# Verify the latest cumulative update is installed on Windows hosts
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 10
# Trigger Windows Update scan and installation via PowerShell
UsoClient StartScan
UsoClient StartDownload
UsoClient StartInstall
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
