CVE-2026-109755 in Firefox
Summary
by MITRE • 10/13/2026
Sandbox escape in the DOM: Content Processes component. This vulnerability was fixed in Firefox 158.
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Analysis
by VulDB Data Team • 10/13/2026
The disclosed security issue represents a critical sandbox escape vulnerability located within the Document Object Model implementation of Mozilla Firefox, specifically affecting the content processes architecture. In modern web browsers, including Firefox, a multi-process architecture is employed to isolate different components of the browsing experience from one another. The main browser process manages user interface elements and privileged operations, while separate content processes handle the rendering and execution of web pages loaded by the user. This separation ensures that malicious code running within a webpage cannot directly access sensitive data or system resources controlled by the parent process. However, this specific vulnerability allows an attacker to bypass these isolation boundaries through carefully crafted interactions with the DOM API, effectively breaking out of the restricted sandbox environment where untrusted content is supposed to be confined.
The technical flaw likely stems from improper validation or handling of object references and permissions when manipulating DOM elements across process boundaries. When a webpage attempts to interact with frames, iframes, or other cross-origin resources via JavaScript, the browser must enforce strict security checks to prevent unauthorized access between contexts. In this instance, the logic governing these interactions failed to correctly restrict certain operations, allowing an attacker who controls malicious content on a web page to execute code in a higher-privilege context. This type of flaw is often categorized under CWE-250, which denotes execution with unnecessary privileges, or potentially CWE-787, if it involves out-of-bounds access leading to arbitrary memory write capabilities that facilitate the escape. The vulnerability exploits the trust relationship between the browser engine and its own internal APIs, turning a feature designed for web compatibility into a vector for privilege escalation within the application itself.
The operational impact of this sandbox escape is severe because it undermines one of the most fundamental security mechanisms in modern browsers: process isolation. Once an attacker successfully escapes the content process sandbox, they gain the ability to execute arbitrary code with the same privileges as the browser's main process. This level of access can lead to remote code execution on the victim's machine without any further user interaction beyond visiting a malicious website or clicking a crafted link. The consequences include full compromise of the system, including theft of stored credentials, session cookies, and sensitive personal data residing in local storage or indexed databases. Furthermore, an attacker could install persistent malware, monitor keystrokes, or use the compromised browser as a pivot point to attack other systems on the network. This vulnerability directly maps to MITRE ATT&CK technique T1059, specifically Command and Scripting Interpreter sub-techniques, as it enables the execution of arbitrary commands within the user's context through the browser application.
To mitigate this risk, users must ensure that their Mozilla Firefox installation is updated to version 158 or later, where the underlying logic governing DOM interactions across process boundaries has been corrected and hardened. Organizations should enforce automated patch management policies to guarantee timely deployment of security updates for all endpoints running affected browsers. Additionally, implementing strict Content Security Policy headers can help limit the impact if a similar vulnerability is exploited in future versions by restricting the sources from which scripts are allowed to load and execute. While no workaround exists that does not involve updating the software itself, maintaining up-to-date browser versions remains the primary defense against such high-severity vulnerabilities that target core rendering engines and process isolation mechanisms.