CVE-2026-117902 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the Layout: Text and Fonts component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/27/2026
The identified vulnerability represents a critical memory management error classified as an out-of-bounds write, specifically manifesting through a use-after-free condition within the Layout: Text and Fonts component of the Mozilla Gecko rendering engine. This type of flaw occurs when the application attempts to access or modify memory that has already been deallocated by the system's garbage collector or explicit free operations. In the context of browser engines, such errors are particularly dangerous because they allow an attacker who controls the content being rendered to manipulate internal data structures before those structures have been properly reallocated or zeroed out. The specific location within the text and font handling subsystem suggests that the vulnerability is triggered during complex layout calculations involving variable fonts, ligatures, or intricate typographic features where memory buffers are frequently allocated and released in rapid succession.
From a technical perspective, this use-after-free scenario likely stems from a race condition or a logic error in reference counting mechanisms governing object lifecycles within the rendering pipeline. When an element containing specific font data is removed from the Document Object Model (DOM) but retains active references due to asynchronous operations such as CSS animations, JavaScript event handlers, or pending layout updates, the underlying memory may be freed prematurely. Subsequent access to this dangling pointer allows for arbitrary read and write capabilities within the browser process space. This capability enables an attacker to overwrite adjacent heap metadata or critical function pointers, which can lead to code execution with the privileges of the user running the browser application. The complexity of modern web pages increases the likelihood of triggering these edge cases during layout recalculations where multiple threads may interact with font metrics and glyph positioning data simultaneously.
The operational impact of this vulnerability is severe, as it facilitates remote code execution through a simple visit to a maliciously crafted webpage or by loading an infected document that utilizes advanced CSS typography features. An attacker could exploit this flaw to bypass modern browser security mitigations such as sandboxing, potentially gaining full control over the victim's system. This level of access allows for data exfiltration, installation of persistent malware, and further lateral movement within a network if the compromised machine is part of an enterprise environment. The risk is amplified by the ubiquity of web-based content delivery mechanisms, meaning that users could be targeted via drive-by downloads or malicious advertisements without any direct interaction beyond visiting a compromised site.
Mitigation strategies primarily rely on timely patching to version Firefox 159 and Firefox ESR 153.6, where Mozilla has addressed the underlying memory management logic in the Gecko engine. Security teams should ensure that all endpoints running affected browser versions are updated immediately through automated deployment tools or manual intervention for critical systems. In environments where immediate patching is not feasible due to compatibility concerns with legacy applications, network-level controls such as web filtering proxies can be configured to block access to known malicious domains hosting exploit kits. Additionally, enabling strict Content Security Policy (CSP) headers on internal websites and restricting the execution of inline scripts can reduce the attack surface by limiting the types of code that can interact with the browser's rendering engine. Continuous monitoring for anomalous network traffic originating from web browsers may also help detect exploitation attempts in real-time before significant damage occurs.