External risk intelligence

Firefox WebAssembly Integer Overflow

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-16369

This vulnerability exists within the WebAssembly component of the Firefox web browser. It is a client-side application issue that requires a user to navigate to malicious content, rather than an internet-facing service, gateway, or network appliance reachable by direct external probes.

Integer Overflow

Mozilla Firefox

before 140.13.0before 153.0.0141.0 to before 153.0

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This advisory addresses a critical vulnerability identified in the WebAssembly component of the Firefox browser. The issue involves an integer overflow that could allow for significant compromise of confidentiality, integrity, and availability. While the vulnerability has been addressed in updated Firefox versions, its potential impact necessitates a review to confirm relevance to our environment.

Integer overflow in browser's WebAssembly.
Could enable significant system compromise.
Confirm relevance and exposure to our environment.

Attack Path

How an attacker could exploit the issue

An attacker could reach this vulnerability by convincing a user to visit a malicious website. The vulnerability exists within the WebAssembly component of the Firefox browser, which processes code that can be used for complex applications. When a specially crafted WebAssembly module is processed, an integer overflow can occur, potentially allowing an attacker to impact the confidentiality, integrity, and availability of the affected system.

No authentication or user interaction required.
Processing malicious WebAssembly code.
Can lead to data compromise and system disruption.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability in Firefox's WebAssembly component could allow an attacker to execute arbitrary code when a user visits a specially crafted webpage. The integer overflow may lead to the corruption of memory used by the browser, potentially impacting the execution of JavaScript and other browser functions.

Browser process memory could be affected.
Through specially crafted web content.
Arbitrary code execution may occur.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in Firefox's WebAssembly component requires a user to visit a malicious website. Ownership likely falls to application or endpoint security teams responsible for user-facing browsers, as well as infrastructure teams ensuring the integrity of end-user devices. The immediate first step is to confirm which users, if any, are running affected versions and are potentially exposed, followed by coordinated remediation or mitigating controls.

Browser owners and endpoint security teams.
Verify affected Firefox versions and user exposure.
Plan targeted updates or deploy mitigating controls.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is Firefox and its WebAssembly component?

Firefox is a widely used web browser designed for navigating the internet. Its WebAssembly (Wasm) component is a specialized engine that allows the browser to run high-performance, complex applications—such as games or video editors—directly within a webpage. By enabling these applications to execute code efficiently at near-native speeds, WebAssembly bridges the gap between traditional software and browser-based experiences.

What does an integer overflow mean in CVE-2026-16369?

An integer overflow occurs when a program tries to store a number larger than its allocated memory space can hold, causing the value to 'wrap around' to an incorrect, often very small or negative, number. In CVE-2026-16369, this weakness (CWE-190) happens within the WebAssembly engine. This calculation error can mislead the browser, potentially allowing an attacker to bypass security checks and manipulate the system's memory.

How does an attacker trigger this vulnerability?

An attacker triggers this bug by enticing a user to visit a website containing a specially crafted WebAssembly module designed to exploit the overflow. The vulnerability is not triggered by standard, safe web browsing or by browsing legitimate sites that do not utilize malicious code. It specifically requires the browser's engine to process the malformed module to initiate the flaw.

Is my environment at risk from this CVE?

Halo Surface Signal notes that this is a client-side issue, meaning the risk is tied to end-user devices rather than servers or network appliances. Unlike vulnerabilities in internet-facing services that can be probed remotely, this requires a user to interact with malicious content. You should focus on endpoints where Firefox is installed, as these are the systems where a user could potentially navigate to a harmful site.

What is the recommended first step for remediation?

The primary step is to identify all systems within your environment currently running Firefox versions older than 153 or ESR 140.13. Once identified, prioritize updating these browsers to the patched versions to eliminate the vulnerability. Because this is a browser-based risk, ensure your endpoint management policies are configured to push these security updates to users promptly.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.