CVE CyberSecurity Database News

CVE-2024-5696 - Firefox, ESR, and Thunderbird Input Tag Vulnerability Exploitation Explained

Poster -

In June 2024, a new high-severity security vulnerability was disclosed and tracked as CVE-2024-5696. This bug affects multiple Mozilla products, including Firefox, Firefox ESR, and Thunderbird. The issue allowed attackers to corrupt memory by manipulating the <input> tag, potentially leading to exploitable crashes and even remote code execution.

In this post, we will break down the details of CVE-2024-5696, explain how the attack works, show a code snippet, and outline what you need to do to stay protected.

What Is CVE-2024-5696?

CVE-2024-5696 relates to the way earlier versions of Firefox and Thunderbird handle text entered or modified in <input> elements. By altering the contents of this tag in a crafted way, an attacker could trigger memory corruption—a serious type of bug that may allow an attacker to crash the browser or, in some cases, run arbitrary code.

Thunderbird < 115.12

If you use any version lower than these, you are vulnerable.

How Does the Exploit Work?

The problem lies in how text is processed and stored when an <input> tag is used. By sending carefully crafted input—via JavaScript or user interaction—an attacker can cause memory to be used incorrectly. This may lead to a crash, or if exploited skillfully, allow the execution of attacker-controlled code.

Attacker creates a specially designed HTML page.

2. The page includes JavaScript that manipulates the contents of an <input> tag in a non-standard way, such as rapidly changing or injecting unexpected characters.

Proof-of-Concept Example

Below is a demonstration snippet that imitates how the exploit could be triggered (please note, this is a benign example and DOES NOT contain real exploit code):

<!-- DO NOT USE FOR MALICIOUS PURPOSES, EDUCATIONAL ONLY -->
<!DOCTYPE html>
<html>
<head>
  <title>CVE-2024-5696 Demo</title>
</head>
<body>
  <input id="dangerous-input" type="text" value="test" />
  <script>
    // Rapidly manipulates the input tag's value in a non-standard way
    let input = document.getElementById('dangerous-input');
    // Fill input with massive, crafted string to stress memory handling
    input.value = 'A'.repeat(100000) + "\uDC00"; // Add a lone surrogate, an invalid char sequence
    // Try to trigger native event handling (previously a source of problems)
    input.dispatchEvent(new Event('input', { bubbles: true }))
  </script>
</body>
</html>

How it works:
This code uses JavaScript to inject an extremely long string (including a Unicode surrogate) into the <input> value, simulating one method attackers could use to confuse how Firefox internally manages the string’s memory.

Real Exploit Details

While the full technical proof-of-concept has not been published by Mozilla for safety, their official advisory describes the risk as follows:

> An attacker could manipulate the text in an <input> tag, causing memory corruption that could result in a crash. With enough skill, this bug could potentially be exploited to run arbitrary code on the target machine.

Exploitation Scenarios

- Malicious website: Visiting a website abusing this bug could crash your browser or (in theory) let an attacker run code on your computer.
- Email attack: Since Thunderbird is vulnerable too, a crafted email with HTML content could potentially be used to exploit users who view it.

- Mozilla Security Advisory 2024-25
- NIST NVD Entry for CVE-2024-5696
- Firefox Release Notes 127

Update immediately: Upgrade Firefox, Firefox ESR, and Thunderbird to the latest versions.

- Do not use outdated software: If you must use an older version for some reason, strictly avoid visiting untrusted sites or opening HTML emails.

Conclusion

CVE-2024-5696 is a strong reminder that browsers are complex pieces of software, and even basic elements like <input> fields can become attack surfaces for advanced hackers. Always keep your applications updated to minimize your risk.

If you're a developer, review how your sites and users interact with input fields. If you’re an everyday user, the number one thing you can do is update your browser now!

Stay safe, and keep your software fresh.

*If this post helped you understand CVE-2024-5696, consider sharing it with friends and coworkers who use Firefox or Thunderbird.*

Timeline

Published on: 06/11/2024 13:15:51 UTC
Last modified on: 08/01/2024 13:59:57 UTC