External risk intelligence

Firefox and Thunderbird Disability Access API Sandbox Escape

CVE advisorySeverity: CRITICAL (CVSS 9.6)

CVE-2026-100800

The vulnerability exists within the Disability Access APIs component of a web browser (Firefox/Thunderbird). This is a client-side component typically executed within the user's local application environment, not a network-facing service, appliance, or infrastructure component exposed to the public internet.

Use After Free

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 critical vulnerability has been identified in a component related to browser accessibility features, specifically within Mozilla's Firefox and Thunderbird products. This issue allows for an escape from a secure browser environment, potentially leading to broader system compromise if exploited. The primary concern at this time is to determine if our organization utilizes the affected software and is therefore exposed.

Browser escape flaw impacts accessibility features.
Critical flaw demands attention to browser security.
Confirm relevance and assess exposure to affected software.

Attack Path

How an attacker could exploit the issue

An attacker could trick a user into visiting a malicious website, which then exploits a flaw in the browser's Disability Access APIs. This could allow them to break out of the browser's security sandbox, leading to significant compromise of the user's system.

Requires user interaction via a malicious website.
Exploits Disability Access APIs in the browser.
Leads to sandbox escape and system compromise.

Live Threat

Current exploitation, exposure, and threat context

A sandbox escape in the Disability Access APIs component could allow an attacker to affect the behavior of the application, potentially leading to unauthorized access to system data or user data when supported by the advisory.

Application data and user data.
Via a specially crafted web page or email.
Application compromise and data exposure.

Operational Fix

Recommended remediation, mitigation, and detection steps

This sandbox escape vulnerability affects client-side components of web browsers, specifically Firefox and Thunderbird. Ownership likely lies with end-user computing or desktop application support teams, with potential coordination needed from platform or security teams if these applications are managed centrally. The first practical step is to identify deployed instances of affected browsers, confirm user impact and business criticality, and then prioritize remediation based on exposure and user risk, possibly involving vendor coordination for updates.

End-user computing or application owners.
Verify affected browser usage and reachability.
Coordinate updates and user communication.

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 APIs component in Firefox and Thunderbird?

This component manages features that help users with disabilities interact with web content, such as screen readers or alternative input devices. It acts as a bridge between the browser's internal engine and the operating system's accessibility services, ensuring that browser data is readable and navigable by specialized assistive technology tools.

What does a use-after-free vulnerability mean for CVE-2026-100800?

This refers to a memory management error (CWE-416) where the software continues to use a memory location after it has been deleted or freed. In this context, an attacker can manipulate this freed memory to gain unauthorized control, effectively breaking out of the security sandbox that normally keeps the browser isolated from your computer's main operating system.

How is this sandbox escape triggered?

An attacker must trick a user into interacting with malicious content, such as visiting a compromised website or opening a malicious email. The bug is not triggered by standard, safe browser usage or by simply having the application installed; it specifically requires the browser to process specially crafted data that exploits the faulty memory handling.

Is my system at risk if I use these browsers?

Halo Surface Signal notes this flaw exists in a client-side component, meaning it is not a network-facing service like a web server. While the browser itself is used to access the internet, the vulnerability relies on local execution within the user's environment. The primary risk is to individual workstations rather than core server infrastructure.

What are the first steps to address CVE-2026-100800?

The most effective response is to update your browser software to the patched versions provided by Mozilla, such as Firefox ESR 153.4 or Thunderbird 157. If you manage these applications centrally, coordinate with your IT or desktop support teams to deploy these updates across your organization to ensure all users are protected.

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.