In the world of Windows security bugs, few things draw the attention of both attackers and defenders like elevation of privilege (EoP) vulnerabilities in core Windows components. That’s why CVE-2022-41100 made a splash when Microsoft patched it in November 2022. This bug affects Windows Advanced Local Procedure Call (ALPC), a system-level IPC (Inter-Process Communication) mechanism, and can allow a local attacker to gain SYSTEM privileges.

If you’re looking to understand this vulnerability, its exploitation, and how to protect yourself, you’ve come to the right place. We’ll break down the vulnerability, walk through public research, and show you a simplified proof-of-concept—all in clear, human language.

What is Windows ALPC?

ALPC, which stands for Advanced Local Procedure Call, is a Windows kernel feature that lets processes talk to each other securely and efficiently. Think of it like a behind-the-scenes telephone line between different Windows services and apps, handling the transmission of commands, data, and status reports.

Because ALPC lives in the kernel and services all sorts of sensitive processes, any bug here means big trouble.

Severity: High

This CVE is distinct from:

CVE-2022-41093

> CVE-2022-41100 is a bug that, when exploited, lets any attacker with local access run code as SYSTEM—essentially giving them total control of the machine.

Vulnerability Details

Microsoft’s official advisory was typically short on specifics, but researchers soon dove into the patch, noting that:

Local users could craft special ALPC messages leading to a privilege elevation.

- The core problem: improper validation of a message or resource, allowing attackers to manipulate or hijack system operations.

The Patch Diff

Several reverse engineers (see references) noticed that Microsoft changed the way ALPC validates certain inputs, ensuring only privileged users could hit critical code paths.

Proof-of-Concept Exploit

Researchers from Zero Day Initiative (ZDI) and others published some details, and working exploits have appeared on GitHub.

Here’s a simplified C-like pseudocode to demonstrate the core idea—abusing an ALPC call to elevate privileges:

// WARNING: This code is for educational purposes only.
#include <windows.h>
#include <stdio.h>
#include <sddl.h>

// Step 1: Open a handle to the ALPC port
HANDLE hAlpcPort = NULL;
UNICODE_STRING portName;
RtlInitUnicodeString(&portName, L"\\RPC Control\\[VulnerablePort]");

// Step 2: Connect to the vulnerable ALPC endpoint
NTSTATUS status = NtAlpcConnectPort(&hAlpcPort, &portName, ...);

if (NT_SUCCESS(status)) {
    // Step 3: Craft a fake (malicious) ALPC message
    ALPC_MESSAGE maliciousMsg = { /* crafted message data */ };

    // Step 4: Send the message to trigger privilege escalation
    status = NtAlpcSendWaitReceivePort(hAlpcPort, , &maliciousMsg, ...);

    if (NT_SUCCESS(status)) {
        // We now have elevated privileges!
        system("cmd.exe");
    }
}

This is an illustration only—the actual exploit requires crafting specific malicious ALPC messages and understanding the affected ALPC port.

In the Wild

There’s no public evidence (as of June 2024) that CVE-2022-41100 has been used in large-scale real-world attacks. But with the knowledge released, opportunistic attackers could target unpatched Windows servers and workstations.

All supported editions of Windows 10 and Windows 11 are patched.

There is NO workaround for unpatched systems. Disabling ALPC is not possible, as it’s critical to Windows stability.

References and Further Reading

- Microsoft Security Advisory for CVE-2022-41100
- Zero Day Initiative Pwn2Own Blog
- Windows ALPC Internals (write-up)
- Example ALPC Exploit on GitHub

Summary

CVE-2022-41100 is a powerful Windows privilege escalation bug in the ALPC subsystem. It’s simple for attackers to abuse—once details are known—and patching immediately is the *only* real solution. Luckily, now you know how it works, why it’s dangerous, and how to stay secure.

*Stay safe, patch often, and keep learning!*

Disclaimer:  
This post is for educational purposes. Exploiting vulnerabilities without permission is illegal and unethical. Always test in isolated, lawful environments.

Timeline

Published on: 11/09/2022 22:15:00 UTC
Last modified on: 11/10/2022 00:33:00 UTC