Browser Certificate Theft by Malicious Code

TL;DR

Yes, malicious Javascript and browser extensions can steal certificates stored in your browser. This is a serious cyber security risk, but there are steps you can take to protect yourself. The main methods involve accessing the browser’s certificate store or intercepting network traffic during SSL/TLS handshakes.

How Certificates Can Be Stolen

1. Accessing the Browser Certificate Store: Browsers store certificates for various purposes (website identification, client authentication). Malicious code can potentially access these stores.
   • Javascript: Javascript running within a compromised website or injected via an extension can use browser APIs to list and export certificates.
   • Browser Extensions: Extensions have broader permissions than regular web pages and can directly interact with the browser’s certificate management features. A rogue extension could extract certificates and send them to a remote server.
2. Man-in-the-Middle (MitM) Attacks: Malicious extensions or code can intercept network traffic, including SSL/TLS handshakes.
   • During the handshake process, certificates are exchanged. The malicious code can capture these certificates before they’re used for encryption.
   • This is more common with poorly configured networks (e.g., using untrusted Wi-Fi) or when a compromised extension controls proxy settings.

Known Cases & Examples

While specific, widely publicised cases are often kept quiet to avoid further exploitation, several examples demonstrate the risk:

• Formjacking Extensions: Some extensions designed to steal form data have also been found with code capable of extracting certificates.
• Malicious Adware/Spyware Bundles: These bundles often include browser hijackers and extensions that can perform certificate theft as part of a wider range of malicious activities.
• Compromised Extension Developers: If an extension developer’s account is compromised, attackers can push updates containing malicious code to existing users.

Protecting Yourself – Step-by-Step Guide

1. Keep Your Browser Updated: Updates often include security patches that address vulnerabilities exploited by malicious code.
   • Chrome automatically updates, but check here to ensure you’re on the latest version.
   • Firefox updates can be managed through Settings > General > Firefox Updates.
2. Review Your Extensions: Regularly check the extensions you have installed.
   • Chrome: chrome://extensions
   • Firefox: about:addons
   • Remove any extensions you don’t recognise or no longer need. Pay attention to permissions requested – be wary of extensions asking for excessive access.
3. Use a Strong Antivirus/Anti-Malware Solution: A good security suite can detect and remove malicious code before it compromises your browser.
4. Be Careful What You Click: Avoid downloading software from untrusted sources. Phishing attacks often lead to compromised websites that inject malicious Javascript.
5. Enable HTTPS Everywhere: This extension forces secure connections whenever possible, reducing the risk of MitM attacks (although it doesn’t prevent certificate theft if the browser itself is compromised).
6. Check Certificate Validity Regularly: While not a direct prevention method, regularly checking your installed certificates can help you identify suspicious entries.
   • Windows: Open ‘Manage user certificates’ (search in Start Menu).
   • macOS: Use Keychain Access.
7. Consider a Hardware Security Key: For sensitive operations, using a hardware security key can protect your private keys from being stolen by browser-based malware.

Technical Details (For Advanced Users)

Malicious Javascript might use code similar to this (this is a simplified example and actual implementations will be more complex):

window.crypto.subtle.getKeyPair("RSA", false, ["exportKey"])
  .then(function(keyPair) {
    // Export the private key
    const exportedPrivateKey = JSON.stringify(keyPair.privateKey);
    console.log(exportedPrivateKey); // Send this to a remote server!
  })
  .catch(function(error) {
    console.error("Error exporting key: ", error);
  });

This code attempts to export the private key associated with an RSA key pair, which could then be sent to a malicious server.