Overview
The vulnerability identified as CVE-2025-4083 is a severe process isolation flaw that affects popular web browser Firefox and email client Thunderbird. This vulnerability is due to the improper handling of javascript: URIs, which could potentially allow malicious content to execute in the top-level document’s process instead of the intended frame. This could enable a sandbox escape, leading to potential system compromise or data leakage. Given the widespread use of Firefox and Thunderbird, this vulnerability is of high importance and requires immediate attention and mitigation.
Vulnerability Summary
CVE ID: CVE-2025-4083
Severity: Critical (CVSS: 9.1)
Attack Vector: Network
Privileges Required: None
User Interaction: Required
Impact: System compromise or data leakage due to potential sandbox escape
Affected Products
No phone number, email, or personal info required.
Product | Affected Versions
Firefox | Versions less than 138
Firefox ESR | Versions less than 128.10 and 115.23
Thunderbird | Versions less than 138 and 128.10
How the Exploit Works
This vulnerability originates from the incorrect handling of javascript: URIs by the affected browsers and email clients. An attacker can exploit this flaw to potentially run malicious content in the top-level document’s process instead of the intended frame. This could lead to a sandbox escape, which would essentially bypass the security measures in place and potentially compromise the system or lead to data leakage.
Conceptual Example Code
Given the nature of this vulnerability, an attacker might craft a malicious web page with a script that exploits the flaw in handling javascript: URIs. While the below example is simplified and conceptual, it illustrates the type of attack that could be performed:
GET /malicious_page.html HTTP/1.1
Host: attacker.example.com
<html>
<body>
<iframe src="javascript:alert('This could be a malicious script executing in top-level document context')">
</iframe>
</body>
</html>In this example, the attacker would attempt to get a user to load the malicious web page in their vulnerable browser. If successful, the malicious script within the iframe would execute in the top-level document’s context, potentially leading to a sandbox escape and further exploitation.
Mitigation
To mitigate this vulnerability, users are strongly advised to apply patches provided by the vendor. For Firefox and Thunderbird, this means upgrading to versions 138 and 128.10 respectively. In the absence of the ability to upgrade, the use of a Web Application Firewall (WAF) or Intrusion Detection System (IDS) could serve as a temporary mitigation measure. However, patching the affected software is the recommended and most effective way to resolve the vulnerability.