CVE-2025-49710: Critical Integer Overflow Vulnerability in Firefox’s JavaScript Engine

Overview

In the world of cybersecurity, vulnerabilities are not taken lightly, and the recently discovered CVE-2025-49710 is no exception. This vulnerability, an integer overflow in the `OrderedHashTable` utilized by Firefox’s JavaScript engine, has severe implications for the integrity, confidentiality, and availability of systems running Firefox versions earlier than 139.0.4. With a CVSS Severity Score of 9.8, this vulnerability is classified as critical, indicating the potential for substantial damage if exploited. In this article, we will delve into the details of this vulnerability, exploring its nature, how it works, and the mitigation strategies available.

Vulnerability Summary

CVE ID: CVE-2025-49710
Severity: Critical (9.8 CVSS score)
Attack Vector: Network
Privileges Required: None
User Interaction: Required
Impact: Potential system compromise or data leakage

Affected Products

Product | Affected Versions

Firefox | < 139.0.4 How the Exploit Works

The vulnerability lies within the `OrderedHashTable` used by Firefox’s JavaScript engine. When an integer overflow occurs within this table, it could potentially lead to a memory corruption. This corruption could then be exploited by an attacker to execute arbitrary code in the context of the user running the affected application.
The exploit can be triggered via a malicious JavaScript that causes the overflow, leading to the corruption. This essentially opens a doorway for the attacker to manipulate the application and impact the system’s integrity, confidentiality, and availability.

Conceptual Example Code

Here is a conceptual example of how the vulnerability might be exploited using a malicious JavaScript code:

let table = new OrderedHashTable(MAX_INT);
for(let i = 0; i <= MAX_INT; i++) {
table.add(i, {value: 'Exploit'});
}
table.add(MAX_INT+1, {value: 'Overflow triggered'});

In this example, a new `OrderedHashTable` is created with the maximum integer value. It then iterates through and adds values up to the maximum integer. When it attempts to add another value beyond the maximum integer, an overflow is triggered, leading to potential memory corruption.

Mitigation

The best way to mitigate this vulnerability is to apply the vendor-supplied patch. In this case, Mozilla, the developer of Firefox, has released version 139.0.4 to address this issue. Users should ensure they are using this version or later to protect their systems.
If immediate patching is not possible, implementing a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can offer temporary mitigation. These systems can help detect and block malicious traffic that attempts to exploit this vulnerability. However, this is not a permanent solution and should be used in conjunction with patching as soon as possible.