CVE-2023-38187 - Elevation of Privilege in Microsoft Edge (Chromium-based) Explained with Code Example and Exploit Breakdown

Published: June 2024

Introduction

On July 2023, Microsoft published a security vulnerability, CVE-2023-38187, affecting Microsoft Edge (Chromium-based). The bug is categorized as an *Elevation of Privilege* (EoP) vulnerability. This means that attackers could use it to gain higher access in a system than they're supposed to have, such as running code as another user or even gaining system privileges.

In this post, we’ll break down how this vulnerability works, show a simplified code snippet to help you understand it, and provide key links and references for further exploration. You'll get a unique, clear perspective on what CVE-2023-38187 is about.

What is CVE-2023-38187?

This vulnerability affects the Chromium-based Microsoft Edge browser. It was possible due to improper validation of privileges when managing browser processes or extension components. A remote attacker who successfully exploited this flaw could perform privileged actions on the victim’s system, which could lead to further compromise.

The official advisory from Microsoft can be found here

- Microsoft Security Update Guide: CVE-2023-38187
- Chromium Security Release Notes

How Does the Vulnerability Work?

At its core, the vulnerability can be exploited via malicious web content or a browser extension that tricks Edge into running code with higher privileges. Attackers exploit the way Edge manages sandboxing and process privileges—if these aren’t properly checked, code designed to have low rights can suddenly perform actions reserved for higher rights, like modifying user files or accessing restricted memory.

Example Scenario

Imagine a user visits a malicious website. That site executes JavaScript, which normally runs within the browser sandbox and has restricted access. Due to CVE-2023-38187, that script could potentially escalate its rights—possibly installing malware or accessing sensitive files.

Code Example: How Sandbox Escape Might Look

The actual exploit code for a vulnerability like this is typically advanced and complex. Here’s a simplified pseudo-code to demonstrate the principle behind elevation attacks in browsers:

// Normally, this script cannot access local files
try {
    // This fails in a normal sandboxed browser
    let data = readLocalFile("C:\\Users\\Alice\\confidential.txt");
    console.log(data); 
} catch (e) {
    console.log("Access denied as expected.");
}

// Exploit steps (simplified example)
if (vulnerableEdgeVersion()) {
    // Step 1: Use flaw to break out of sandbox
    privilegeEscalate();
    // Step 2: Access restricted data
    let secret = readLocalFile("C:\\Users\\Alice\\confidential.txt");
    sendToAttacker(secret);
}

*Note: This is pseudocode for educational purposes. In real life, attackers chain several flaws together, including memory corruption, to achieve a sandbox escape.*

Proof-of-Concept Exploit (Overview)

At the time of writing, there is no working public proof-of-concept (PoC) exploit for CVE-2023-38187, due to the risk of widespread abuse and responsible disclosure policies. However, generally, an exploit could:

Detect the vulnerable Edge version.

2. Feed crafted input (such as a specially designed extension or heaped JavaScript) to exploit the flawed privilege check.

Example Exploit Outline (in theory)

# This Python pseudo-code outlines steps an attacker might take
import requests

def check_vulnerable_edge():
    # Check browser version via User-Agent
    pass

def trigger_vulnerability():
    # Serve malicious JavaScript or extension
    pass

def execute_payload():
    # Read or modify privileged data
    pass

if check_vulnerable_edge():
    trigger_vulnerability()
    execute_payload()

Limit the use of untrusted extensions: Only install extensions from trusted sources.

- Antivirus and endpoint protection: Maintain protection measures in case an attacker breaks initial controls.

Microsoft patched this vulnerability in Edge version 115..1901.203, released in August 2023.

References

- Microsoft Security Advisory: CVE-2023-38187
- Edge for Business Release Notes
- Chromium Security Blog
- OWASP Browser Sandboxing Overview

Conclusion

CVE-2023-38187 is a significant lesson in the importance of proper privilege management, especially in applications like web browsers that handle code from untrusted sources every day.
By promptly updating your browser and being careful with extensions, you can minimize the risk. If you’re interested in more technical details, look for talks from security conferences or follow updates from Chromium and Microsoft security blogs.

*Stay safe, and keep your software up to date!*

> Written exclusively for educational use. No encouragement of malicious use. Always follow ethical and legal standards.

Timeline

Published on: 07/21/2023 18:15:00 UTC
Last modified on: 08/01/2023 15:35:00 UTC