CVE-2026-92018 in Firefox
Summary
by MITRE • 09/15/2026
Sandbox escape in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 156, Firefox ESR 115.41, Firefox ESR 140.16, and Firefox ESR 153.3.
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Analysis
by VulDB Data Team • 09/15/2026
The identified security issue represents a critical failure in the browser's sandboxing mechanisms within the Document Object Model core and HTML components of Mozilla Firefox. This vulnerability allows content running with restricted privileges to escape its intended execution context and gain access to higher-privilege areas or resources that should remain inaccessible. In modern web browsers, the principle of least privilege is enforced through a multi-layered security architecture designed to isolate untrusted web content from the host operating system and other browser processes. When this isolation breaks down due to flaws in how DOM elements are processed or validated, it creates an avenue for attackers to bypass these protective boundaries. The specific nature of this flaw suggests that certain operations involving HTML parsing or DOM manipulation were not adequately sanitized or checked against expected constraints, allowing maliciously crafted input to trigger unintended side effects within the privileged browser environment.
From a technical perspective, such sandbox escapes often stem from race conditions, type confusion errors, or improper handling of object references during the rendering and scripting phases. An attacker could potentially exploit this by constructing a specially designed webpage that triggers the vulnerable code path when rendered in Firefox. By leveraging specific combinations of HTML tags, JavaScript APIs, and CSS properties, it may be possible to manipulate internal browser structures in ways that were not anticipated by the developers. This manipulation can lead to arbitrary memory reads or writes, which are foundational techniques for achieving full system compromise if combined with other exploits. The impact is severe because a successful sandbox escape effectively neutralizes one of the most important defenses against web-based attacks, allowing malicious scripts to interact directly with browser internals and potentially access sensitive user data such as cookies, stored passwords, or session tokens without explicit permission from the user.
The operational impact of this vulnerability extends beyond simple privilege escalation within the browser context. If an attacker successfully exploits this flaw, they can execute arbitrary code on the victim's machine under the security context of the Firefox process. This means that any data accessible to the browser becomes exposed, including information stored in local storage, IndexedDB, and other web technologies. Furthermore, depending on how the sandbox escape is implemented, it might allow for further exploitation vectors such as kernel-level attacks if additional vulnerabilities are present in underlying system libraries accessed by the browser. The risk is particularly acute given that Firefox remains one of the most widely used browsers globally, making any widespread exploit highly impactful from a threat actor's perspective. Users who visit compromised or maliciously hosted websites could find their systems fully compromised without any further interaction required beyond loading the page.
To mitigate this risk, it is imperative to update Mozilla Firefox and its Extended Support Release (ESR) variants immediately. The vulnerability has been addressed in Firefox version 156 as well as specific maintenance releases for ESR branches including versions 115.41, 140.16, and 153.3. These updates contain the necessary patches that correct the logic errors within the DOM core and HTML components responsible for the sandbox escape. Organizations relying on Firefox should ensure their deployment pipelines are configured to automatically apply these security updates as soon as they become available in their respective update channels. For users who cannot immediately patch, employing additional layers of defense such as strict content security policies, disabling JavaScript execution on untrusted sites via browser extensions, and maintaining up-to-date antivirus software can provide some degree of protection against exploitation attempts until the underlying vulnerability is remediated.
This incident aligns with common attack patterns documented in industry standards for web application vulnerabilities. Specifically, it relates to CWE-250 which describes Execution with Unnecessary Privileges, as well as CWE-94 where improper control of generation of code or commands leads to security flaws. In the context of the MITRE ATT&CK framework, this type of vulnerability facilitates techniques associated with Initial Access and Defense Evasion, particularly those involving browser exploitation for privilege escalation. Understanding these classifications helps in categorizing similar future incidents and refining detection rules within enterprise security monitoring tools. By recognizing that sandbox escapes are a primary vector for advanced persistent threats targeting web browsers, security teams can prioritize patch management and behavioral analysis to detect anomalous activities resulting from such exploits before they lead to significant data breaches or system compromises.