Overview
This blog post explores the critical vulnerability CVE-2025-6424, a use-after-free flaw discovered in FontFaceSet. This flaw can potentially lead to an exploitable crash, impacting users of Firefox versions up to 140, Firefox ESR up to 115.25, and Firefox ESR up to 128.12. Given the widespread use of Firefox around the world, the severity of this vulnerability is significant, with a potential for system compromise or data leakage. In an era where data security is paramount, addressing this vulnerability is of utmost importance.
Vulnerability Summary
CVE ID: CVE-2025-6424
Severity: Critical (CVSS: 9.8)
Attack Vector: Remote
Privileges Required: None
User Interaction: Required
Impact: Potential system compromise or data leakage
Affected Products
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Product | Affected Versions
Firefox | < 140 Firefox ESR | < 115.25 Firefox ESR | < 128.12 How the Exploit Works
The vulnerability originates from a use-after-free condition in FontFaceSet. This occurs when the program continues to use a pointer after it has been freed. This can lead to two potential issues, either the program will crash when it attempts to access the freed memory, or it could lead to the execution of arbitrary code if the attacker can control what is placed at the memory location, which is freed. In this case, it results in a potentially exploitable crash that could lead to system compromise or data leakage.
Conceptual Example Code
While no specific exploit code is available for this flaw, the following pseudocode provides a conceptual idea of how an attacker might exploit a use-after-free vulnerability:
// The attacker convinces the user to run a script on a web page
let evil_script = () => {
fontFaceSet = document.fonts;
fontFaceSet.clear(); // This frees the FontFaceSet object
fontFaceSet.load('font_name'); // This would attempt to use the freed FontFaceSet
};
// The malicious script is executed when the user visits a page
window.onload = () => {
evil_script();
};This code illustrates a scenario where an attacker could manipulate the user into executing a script that attempts to use a freed FontFaceSet object, triggering the use-after-free vulnerability.