CVE-2026-21232: Windows 11 23h2 Privilege Escalation Flaw

CVE-2026-21232 Overview

CVE-2026-21232 is an untrusted pointer dereference vulnerability in Windows HTTP.sys that allows an authorized attacker to elevate privileges locally. This vulnerability affects the kernel-mode driver responsible for handling HTTP requests in Windows, making it a significant security concern for both client and server Windows deployments.

Critical Impact

Local privilege escalation via untrusted pointer dereference in HTTP.sys could allow attackers with local access to gain SYSTEM-level privileges, potentially leading to complete system compromise.

Affected Products

• Microsoft Windows 11 23H2 (x64 and ARM64)
• Microsoft Windows 11 24H2 (x64 and ARM64)
• Microsoft Windows 11 25H2 (x64 and ARM64)
• Microsoft Windows Server 2022 23H2
• Microsoft Windows Server 2025

Discovery Timeline

• February 10, 2026 - CVE-2026-21232 published to NVD
• February 11, 2026 - Last updated in NVD database

Technical Details for CVE-2026-21232

Vulnerability Analysis

The vulnerability exists within the Windows HTTP Protocol Stack (HTTP.sys), a kernel-mode driver that processes HTTP requests. An untrusted pointer dereference occurs when the driver fails to properly validate memory pointers before dereferencing them. This flaw (CWE-822: Untrusted Pointer Dereference) allows an attacker with local access to craft malicious input that causes the driver to dereference an attacker-controlled memory address.

The attack requires local access to the system and low privileges to execute, but does not require any user interaction. Upon successful exploitation, an attacker can achieve elevated privileges that could affect the confidentiality, integrity, and availability of the compromised system.

Root Cause

The root cause of this vulnerability is classified as CWE-822 (Untrusted Pointer Dereference). This weakness occurs when HTTP.sys accepts pointer values from an untrusted source and dereferences them without adequate validation. The kernel-mode driver fails to verify that the pointer refers to a valid, expected memory location before attempting to read or write data at that address. This allows attackers to manipulate program control flow or access arbitrary kernel memory.

Attack Vector

The attack vector is local, meaning an attacker must have authenticated local access to the target system. The attacker can exploit this vulnerability by sending specially crafted requests to the HTTP.sys driver that include malicious pointer values. Since HTTP.sys operates in kernel mode, successful exploitation allows the attacker to escalate from a low-privileged user context to SYSTEM-level privileges.

The exploitation mechanism involves manipulating memory addresses that the vulnerable code path uses for pointer dereference operations. When the kernel driver processes the malicious input, it inadvertently follows the attacker-controlled pointer, leading to privilege escalation.

Detection Methods for CVE-2026-21232

Indicators of Compromise

• Unusual process behavior from services or applications interacting with HTTP.sys
• Unexpected privilege escalation events in Windows Security Event logs
• Anomalous kernel memory access patterns or crash dumps related to HTTP.sys
• Suspicious local authentication followed by rapid privilege changes

Detection Strategies

• Monitor Windows Event Logs for Event ID 4688 (Process Creation) with anomalous parent-child process relationships
• Deploy endpoint detection rules for suspicious interactions with the HTTP Protocol Stack
• Utilize kernel-mode monitoring to detect abnormal memory access patterns in HTTP.sys
• Implement SentinelOne Singularity XDR to detect and correlate privilege escalation attempts

Monitoring Recommendations

• Enable Windows Defender Exploit Protection with Attack Surface Reduction (ASR) rules
• Configure Windows Event Forwarding to centralize security events for analysis
• Deploy SentinelOne agents with behavioral AI to detect exploitation attempts in real-time
• Implement file integrity monitoring on critical system drivers including HTTP.sys

How to Mitigate CVE-2026-21232

Immediate Actions Required

• Apply the latest security updates from Microsoft immediately
• Review and restrict local user access to minimize potential attack surfaces
• Enable Windows Defender Credential Guard and other security features
• Audit systems for signs of compromise before and after patching

Patch Information

Microsoft has released security updates to address this vulnerability. Detailed patch information and download links are available in the Microsoft Security Update Guide for CVE-2026-21232. Organizations should prioritize deploying these updates to all affected Windows 11 and Windows Server systems.

Workarounds

• Limit local access to systems running affected Windows versions to trusted users only
• Implement network segmentation to reduce lateral movement opportunities
• Monitor and restrict applications that interact directly with HTTP.sys
• Consider disabling HTTP.sys-dependent services if not required for business operations

# Verify HTTP.sys driver version after patching
driverquery /v | findstr /i "http.sys"

# Check Windows Update status
wmic qfe list brief | findstr /i "KB"