CVE-2026-25184: AppLocker Privilege Escalation Vulnerability

CVE-2026-25184 Overview

CVE-2026-25184 is a race condition vulnerability in the Windows AppLocker Filter Driver (applockerfltr.sys) that allows an authorized local attacker to escalate privileges. This vulnerability stems from concurrent execution using a shared resource with improper synchronization (CWE-362), enabling authenticated users to gain elevated system privileges through careful timing manipulation of driver operations.

Critical Impact

Successful exploitation allows local attackers with low-level access to escalate privileges to SYSTEM level, potentially compromising the entire Windows system and bypassing AppLocker security controls.

Affected Products

• Microsoft Windows with AppLocker enabled
• Windows AppLocker Filter Driver (applockerfltr.sys)

Discovery Timeline

• April 14, 2026 - CVE-2026-25184 published to NVD
• April 14, 2026 - Last updated in NVD database

Technical Details for CVE-2026-25184

Vulnerability Analysis

This vulnerability exists within the AppLocker Filter Driver, a kernel-mode component responsible for enforcing application control policies in Windows environments. The race condition occurs when the driver processes concurrent requests involving shared resources without proper synchronization primitives.

The vulnerability requires local access and low privileges to exploit, though the attack complexity is high due to the precise timing requirements inherent in race condition exploitation. A successful attack can result in complete compromise of confidentiality, integrity, and availability of the affected system, as the attacker gains elevated kernel-level privileges.

AppLocker is designed as a security feature to control which applications users are allowed to run, making this privilege escalation particularly concerning as it undermines the security boundary AppLocker is intended to enforce.

Root Cause

The root cause of CVE-2026-25184 is a Time-of-Check Time-of-Use (TOCTOU) race condition within the applockerfltr.sys driver. The driver fails to properly serialize access to shared resources during policy evaluation or request handling, creating a window where an attacker can manipulate the state between when a security check is performed and when the corresponding action is executed.

This improper synchronization allows a malicious local user to exploit the timing gap to bypass security checks or manipulate data structures in a way that grants elevated privileges.

Attack Vector

The attack vector for this vulnerability is local, requiring the attacker to have authenticated access to the target system with at least low-level user privileges. Exploitation involves:

1. Identifying the vulnerable code path within the AppLocker Filter Driver that processes requests without proper locking
2. Creating multiple concurrent threads or processes that interact with the driver simultaneously
3. Precisely timing operations to win the race condition, manipulating the driver state between security validation and privileged operations
4. Leveraging the resulting inconsistent state to execute code with SYSTEM privileges

The attack does not require user interaction and, if successful, provides the attacker with complete control over the affected system. However, the high attack complexity means reliable exploitation requires sophisticated timing and may not succeed on every attempt.

Detection Methods for CVE-2026-25184

Indicators of Compromise

• Unusual process spawning with SYSTEM privileges from low-privileged user sessions
• Abnormal thread activity involving the applockerfltr.sys driver
• Unexpected AppLocker policy bypass events in Windows Event Logs
• Signs of exploitation tools targeting Windows kernel drivers

Detection Strategies

• Monitor for suspicious kernel driver interactions through Windows ETW (Event Tracing for Windows) providers
• Enable detailed AppLocker auditing to detect policy enforcement anomalies
• Deploy endpoint detection rules for privilege escalation patterns involving driver race conditions
• Utilize SentinelOne's behavioral AI to detect anomalous privilege transitions from user-mode to kernel-mode

Monitoring Recommendations

• Enable Windows Security Event Log auditing for privilege use events (Event ID 4672, 4673)
• Monitor AppLocker-specific events in the Microsoft-Windows-AppLocker/EXE and DLL operational log
• Implement real-time monitoring of driver loading and kernel object manipulation
• Use SentinelOne Singularity platform for continuous monitoring of kernel-level threats

How to Mitigate CVE-2026-25184

Immediate Actions Required

• Apply the latest Windows security updates from Microsoft as soon as they are available
• Review systems for signs of exploitation attempts
• Ensure all systems with AppLocker enabled are prioritized for patching
• Restrict local access to sensitive systems to minimize the attack surface

Patch Information

Microsoft has released security guidance for this vulnerability. System administrators should consult the Microsoft Vulnerability Advisory for official patch information and apply relevant security updates through Windows Update or WSUS.

Patches should be tested in non-production environments before wide deployment, and organizations should prioritize systems where AppLocker is actively used for application control.

Workarounds

• Limit local user access on systems where AppLocker is deployed for security-critical functions
• Consider temporarily disabling AppLocker on non-essential systems until patches are applied (understanding this removes application control protections)
• Implement additional monitoring and access controls to detect and prevent privilege escalation attempts
• Use SentinelOne's Singularity platform to provide runtime protection against exploitation attempts

Organizations unable to immediately patch should implement compensating controls such as enhanced monitoring and strict access controls while working toward full remediation.