CVE-2026-100800 in Firefox
Summary
by MITRE • 09/29/2026
Sandbox escape due to use-after-free in the Disability Access APIs component. This vulnerability was fixed in Firefox ESR 153.4 and Firefox 157.
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Analysis
by VulDB Data Team • 09/29/2026
The identified security flaw resides within the Disability Access APIs subsystem of Mozilla Firefox, specifically manifesting as a use-after-free condition that facilitates sandbox escape. In modern web browsers, the rendering engine operates under strict privilege separation models where untrusted content from websites runs in restricted sandboxes to prevent malicious actors from accessing sensitive system resources or user data. The disability access features are designed to assist users with impairments by exposing internal browser structures and UI elements to external accessibility tools such as screen readers. This necessary exposure creates a complex attack surface because the accessibility API must maintain references to various DOM nodes, widgets, and interface components while they are being manipulated, created, or destroyed during normal browsing activities.
The technical root cause of this vulnerability is a classic use-after-free error within the memory management logic governing these access interfaces. When an object representing an accessible element is removed from the document tree or otherwise invalidated by the browser engine, its underlying memory should be immediately released and any dangling pointers to that memory must be nullified. However, due to a flaw in the reference counting mechanism or lifecycle management of the Disability Access APIs component, certain references persisted after the original object had been deallocated. This creates a window where an attacker can trigger specific sequences of DOM manipulation events to cause the browser to free critical data structures while retaining active pointers that still point to those freed memory regions.
By exploiting this use-after-free condition, a malicious actor executing JavaScript within a compromised webpage or extension can manipulate the state of these dangling pointers. Through careful heap grooming and precise timing attacks, it is possible to reallocate the freed memory with attacker-controlled data structures. When the browser subsequently attempts to access the accessibility information through the stale pointer, it inadvertently reads from or writes to this controlled memory region. This arbitrary read-write primitive allows the adversary to corrupt internal browser state variables, such as function pointers or security flags, effectively breaking out of the restrictive sandbox environment and gaining code execution with the privileges of the parent process.
The operational impact of successfully exploiting this vulnerability is severe, as it leads to a complete compromise of the user's browsing session and potentially the underlying operating system. Once inside the browser process without sandbox restrictions, an attacker can access local files, steal cookies and authentication tokens stored in memory, inject malicious code into other tabs or windows, and perform keylogging activities undetected by standard security controls. This level of privilege escalation undermines the fundamental trust model of web browsers, allowing remote attackers to turn a simple visit to a malicious website into a full system compromise without any user interaction beyond loading the page.
This vulnerability aligns with CWE-416, which describes use-after-free conditions where memory is accessed after it has been freed, leading to undefined behavior and potential exploitation. From an offensive security perspective, this attack vector maps directly to MITRE ATT&CK technique T1055.012, Process Injection via Memory Allocation, as well as techniques related to privilege escalation within the context of client-side software abuse. The ability to escape the sandbox is a critical failure in defense-in-depth strategies that rely on process isolation to contain threats originating from untrusted web content.
Mitigation for this vulnerability requires immediate application of the patches released in Firefox ESR 153.4 and Firefox 157, which address the memory management flaws within the accessibility API subsystem. Organizations relying on extended support releases should prioritize updating their fleets to ensure compliance with security baselines that mandate protection against sandbox escape vulnerabilities. For users unable to update immediately due to compatibility constraints, deploying network-level controls such as web filtering proxies can help block access to known malicious domains attempting to exploit this flaw. Additionally, enabling strict content security policies and disabling unnecessary browser extensions reduces the attack surface available for triggering the specific DOM manipulation sequences required to trigger the use-after-free condition.