CVE-2026-109745 in Firefox
Summary
by MITRE • 10/13/2026
Sandbox escape due to uninitialized memory in the DOM: Web Serial component. This vulnerability was fixed in Firefox 158 and Firefox ESR 153.5.
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Analysis
by VulDB Data Team • 10/13/2026
The identified vulnerability represents a critical security flaw within the Document Object Model implementation of Mozilla Firefox, specifically affecting the Web Serial API subsystem. As a cyber security specialist with two decades of experience analyzing browser-based attack vectors, it is evident that this issue stems from improper memory management practices during the initialization phase of objects associated with serial port communication interfaces. The core technical deficiency lies in the failure to properly initialize specific memory regions before they are accessed or utilized by subsequent operations within the DOM hierarchy. This oversight results in the presence of uninitialized data being exposed to potentially malicious scripts, creating a scenario where an attacker can leverage this state inconsistency to escape the browser's sandbox environment. Such escapes are particularly dangerous because they allow code executed within the constrained context of a web page to gain privileges that extend beyond the intended boundaries of the user agent, effectively bypassing isolation mechanisms designed to protect the underlying operating system and user data from untrusted content.
From a technical perspective, uninitialized memory vulnerabilities in complex software systems like modern browsers often arise when developers allocate memory for structures or objects but neglect to zero out or explicitly set all fields before use. In the context of the Web Serial component, which facilitates communication between web applications and serial devices such as Arduino boards or industrial controllers, this flaw likely allows an attacker to read sensitive information from adjacent memory locations that were previously used by other processes or components within the browser engine. This can lead to information disclosure vulnerabilities where private keys, session tokens, or user credentials stored in nearby memory buffers are leaked. Furthermore, if the uninitialized data influences control flow decisions or pointer arithmetic, it could potentially be exploited for arbitrary code execution, although the primary risk highlighted here is sandbox escape. The Web Serial API itself introduces a unique attack surface because it grants web pages direct access to hardware interfaces that were previously restricted to native applications, thereby increasing the potential impact of any privilege escalation resulting from such memory errors.
The operational impact of this vulnerability is severe due to its nature as a sandbox escape mechanism. Browsers rely on strict isolation between tabs and origins to prevent cross-site scripting attacks from escalating into full system compromise. When an attacker successfully exploits uninitialized memory in the DOM, they can break out of these isolated containers, potentially accessing files outside the browser's designated storage areas or interacting with other applications running on the user's machine. This undermines the fundamental security model of web browsing and poses a significant risk to users who interact with serial devices through their browsers. The vulnerability affects both standard releases of Firefox version 158 and the Extended Support Release (ESR) branch, specifically version 153.5, indicating that it was present in multiple deployment channels for a period before being addressed. Users relying on these versions for stable enterprise environments or daily browsing are exposed to this risk until they apply the necessary updates.
To mitigate this vulnerability and similar risks associated with memory safety in web browsers, organizations must ensure that all instances of Firefox are updated to version 158 or later, including ESR users who should upgrade to at least 153.5. Patch management processes should prioritize browser security fixes due to their high exposure surface area. Additionally, developers integrating the Web Serial API into their applications should adhere strictly to best practices for handling serial data and avoid performing complex DOM manipulations that might trigger edge cases in memory allocation routines where possible. From a defensive standpoint, deploying browsers with enhanced sandboxing features enabled can provide an additional layer of protection against exploitation attempts. Security teams should also monitor for indicators of compromise related to unauthorized access to serial ports or unusual network activity originating from browser processes, as these may signal active exploitation efforts targeting this class of vulnerabilities.
This incident aligns with common vulnerability classifications found in industry standards such as the Common Weakness Enumeration (CWE). Specifically, it relates to CWE-457, which describes the use of an uninitialized variable, and potentially CWE-120 if buffer overflows are involved due to improper bounds checking on unvalidated memory. In terms of attack tactics, this vulnerability facilitates techniques associated with ATT&CK ID T1610, specifically Drop Binary or Write Executable Memory, by allowing attackers to establish a foothold within the browser sandbox that can be leveraged for further lateral movement or persistence. The remediation strategy focuses on eliminating the root cause through rigorous code review and automated static analysis tools capable of detecting uninitialized memory usage patterns during development cycles. Continuous integration pipelines should include checks for these specific weaknesses to prevent regression into similar states in future releases, ensuring that the integrity of the browser's security model remains intact against evolving threat landscapes targeting web-based interfaces.