External risk intelligence

Firefox Disability Access API Sandbox Escape

CVE advisorySeverity: CRITICAL (CVSS 10.0)

CVE-2026-4688

The vulnerability exists within the Disability Access APIs component of a web browser. As a client-side component, it is not an internet-facing service or listener, and exploitation requires the user to interact with malicious content, making it fundamentally different from public-facing infrastructure like web servers or gateways.

Use After Free

Mozilla Firefox

before 140.9.0before 149.0

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

A vulnerability in the Disability Access APIs component of certain Mozilla products could allow an attacker to escape the browser's sandbox. This flaw, which is critical in severity, has been addressed in recent updates. The main concern is to confirm if any affected systems are in use.

Sandbox escape in browser accessibility features.
Confirms exposure of critical browser functionality.
Verify if affected browsers are in use.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by tricking a user into visiting a malicious website or opening a specially crafted file. This would trigger a use-after-free condition within the browser's Disability Access APIs. Successful exploitation could allow an attacker to escape the browser's sandbox, potentially leading to a complete compromise of the user's system.

Requires network access and no privileges.
Triggers use-after-free in Disability Access APIs.
Allows sandbox escape and system compromise.

Live Threat

Current exploitation, exposure, and threat context

A use-after-free vulnerability in the Disability Access APIs component could allow an attacker to escape the browser's sandbox when supported by the advisory. This could potentially affect the system data and service behavior of the affected application.

System data and service behavior could be affected.
Attackers could exploit a sandbox escape.
Malicious code could execute within the system.

Operational Fix

Recommended remediation, mitigation, and detection steps

The Disability Access APIs component in Firefox and Thunderbird is affected by a sandbox escape vulnerability. In a real-world scenario, application owners and infrastructure teams are typically responsible for managing browser deployments. The first practical step is to identify all instances of the affected software, determine their exposure and criticality, and then coordinate with vendor management for the necessary updates.

Browser and application owners should manage this issue.
Verify all affected Firefox and Thunderbird instances.
Plan for vendor-provided updates and deployments.

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 the Disability Access API component in Firefox?

These APIs are built-in features that help the browser communicate with assistive technologies, such as screen readers, to make web content accessible to users with disabilities. By integrating with the operating system, they ensure that UI elements and web data are readable by those tools. While essential for inclusivity, this deep integration between the browser's internal logic and system-level functions creates the complex interface where this security flaw resides.

What does a use-after-free vulnerability mean for CVE-2026-4688?

This is a memory management error classified as CWE-416. It occurs when the software continues to use a memory location after it has been cleared or released. Because the Disability Access APIs mistakenly reference this 'stale' memory, an attacker can manipulate it to override normal program behavior. In the context of this CVE, this defect allows an attacker to break out of the browser's sandbox, which is the security boundary designed to prevent web code from affecting your main system.

How is this vulnerability triggered?

The flaw is triggered when a user interacts with malicious content, such as navigating to a compromised website or opening a specially crafted file that forces the browser to mishandle memory within the accessibility component. Simply having the browser installed is not enough to trigger the bug. It requires an active process where the browser renders untrusted content, which then activates the vulnerable code path in the Disability Access APIs.

Is my system at risk if it isn't internet-facing?

Halo Surface Signal notes this as very unlikely for infrastructure because browsers are client-side applications, not internet-facing services or listeners. However, risk remains if a user on that system browses the web. Since the vulnerability requires user interaction with external content to exploit, internal systems are not immune if they are used to access the web or open untrusted documents, even if they do not host public-facing services.

What are the first steps to address this issue?

Prioritize identifying all installations of Firefox and Thunderbird within your environment to see if they fall below the fixed versions: 149 for Firefox or 140.9 for the ESR and Thunderbird editions. Once identified, coordinate the standard update process to ensure these browsers are patched to the latest versions. Since this is a browser-level update, ensure that any deployment schedules account for testing and consistent rollout across your user base.

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.