CVE-2026-117875 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the Layout: Scrolling and Overflow component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/28/2026
The identified vulnerability represents a critical memory management error within the Mozilla Gecko rendering engine, specifically located in the subsystem responsible for handling layout calculations related to scrolling regions and overflow properties. As a use-after-free defect, this flaw occurs when the application attempts to access memory that has already been deallocated by the system. In the context of web browser engines, such errors are particularly dangerous because they can be triggered through standard HTML and CSS constructs embedded in maliciously crafted websites or documents. The vulnerability arises from an inconsistency in how references to layout objects are maintained during dynamic updates to page structure, where a pointer remains valid logically but points to freed memory physically.
From a technical perspective, the flaw likely involves a race condition or improper lifecycle management of DOM elements that affect scrollable containers. When a user interacts with a webpage containing complex overflow scenarios, such as nested scrolling divs or dynamically resized content areas, the browser may release internal data structures associated with those elements before all references to them are cleared. If subsequent operations attempt to read from or write to these dangling pointers, it results in undefined behavior. This can lead to memory corruption, which attackers leverage to execute arbitrary code within the context of the victim's browser process. The severity is heightened by the fact that modern browsers employ various sandboxing techniques, but a successful exploitation could potentially allow an attacker to bypass certain security boundaries if combined with other vulnerabilities or specific exploit chains targeting the rendering engine’s isolation mechanisms.
The operational impact of this vulnerability is severe for end-users who browse untrusted content without adequate protection layers. An attacker can craft a malicious webpage that automatically triggers the scrolling and overflow conditions upon loading, requiring no user interaction beyond visiting the site. Successful exploitation could lead to remote code execution, allowing the compromise of the underlying operating system or access to sensitive data stored locally by the browser, such as cookies, session tokens, and saved passwords. Furthermore, memory corruption issues often serve as a stepping stone for more advanced attacks, including privilege escalation if the browser process runs with elevated permissions in certain enterprise environments. The lack of user interaction required makes this vulnerability highly attractive for drive-by download campaigns and automated exploitation kits distributed across the dark web or compromised advertising networks.
Mitigation strategies primarily rely on timely software updates to apply the patches released by Mozilla. Users should ensure that their Firefox installations, including both standard releases like version 159 and extended support release versions such as 153.6, are updated immediately upon availability. For organizations managing large fleets of browsers, automated patch management systems should be configured to prioritize these updates due to the high severity associated with memory corruption flaws in rendering engines. Additionally, deploying browser hardening techniques can provide defense-in-depth measures. These include enabling site isolation features which restrict how much data different websites can access from each other, thereby limiting the potential impact of a successful exploit. Security awareness training for employees regarding suspicious links and untrusted web content also serves as a vital human layer of protection against social engineering tactics that might lead users to vulnerable pages before patches are applied.
This vulnerability aligns with Common Weakness Enumeration category CWE-416, which defines use-after-free errors where memory is reused after it has been freed, leading to unpredictable behavior and potential security breaches. In terms of the MITRE ATT&CK framework, this flaw facilitates techniques associated with initial access via drive-by compromise or execution through browser exploitation. Attackers typically leverage such vulnerabilities in conjunction with exploit kits that automate the delivery of shellcode once memory corruption is achieved. The specific component involved highlights the complexity of modern web standards implementation and underscores the importance of rigorous code review processes for critical infrastructure components like layout engines, which are frequently targeted due to their central role in rendering user-facing content. Continuous monitoring for anomalous browser behavior and keeping security software updated further reduces the attack surface presented by such high-severity memory safety issues.