CVE-2026-109705 in Firefox
Summary
by MITRE • 10/13/2026
Sandbox escape, site isolation issue due to incorrect boundary conditions, use-after-free in the Networking component. This vulnerability was fixed in Firefox 158 and Firefox ESR 153.5.
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Analysis
by VulDB Data Team • 10/14/2026
The reported vulnerabilities represent a critical convergence of memory safety errors and architectural security failures within Mozilla's Gecko rendering engine, specifically targeting the networking subsystem and browser sandboxing mechanisms. These issues were addressed in Firefox version 158 and Firefox Extended Support Release (ESR) version 153.5, marking significant improvements to the browser's resilience against exploitation attempts that leverage complex state management errors during network operations.
The site isolation issue stems from incorrect boundary conditions within the sandboxing architecture designed to enforce strict separation between different web origins. Site isolation is a fundamental defense-in-depth strategy employed by modern browsers to prevent cross-site scripting and data theft attacks, such as Spectre or side-channel information leaks, by ensuring that sensitive processes are isolated in separate operating system-level containers. When boundary conditions are miscalculated during the initialization or termination of these sandboxed contexts, it can lead to a failure in enforcing these isolation boundaries. This flaw allows maliciously crafted web content to potentially escape its designated security zone and interact with resources belonging to other origins that should remain inaccessible. Such an escape undermines the core trust model of the browser, enabling attackers to read sensitive data from protected tabs or execute code within higher-privilege contexts than intended by the sandbox policy.
Concurrently, a use-after-free vulnerability was identified in the Networking component, which handles HTTP requests, WebSocket connections, and other network-related tasks. This type of memory corruption error occurs when an application continues to use a pointer after it has been freed or deallocated from memory. In the context of browser networking, this often happens during asynchronous operations where objects are destroyed while pending callbacks or event handlers still hold references to them. If an attacker can trigger specific network conditions that cause premature object destruction followed by immediate access through stale pointers, they may achieve arbitrary code execution with the privileges of the compromised process. This is particularly dangerous because it bypasses many modern memory protection mechanisms like Address Space Layout Randomization (ASLR) and Data Execution Prevention (DEP), allowing for direct control over program flow.
The operational impact of these combined vulnerabilities is severe, as they provide multiple vectors for remote code execution on a victim's machine without requiring physical access or user interaction beyond visiting a malicious website. An attacker could craft a specially designed webpage that exploits the site isolation boundary failure to gain broader context awareness and then leverages the use-after-free flaw in the networking stack to execute arbitrary commands. This effectively compromises the integrity, confidentiality, and availability of the user's system, potentially leading to full device takeover depending on the execution environment and additional local vulnerabilities present.
From a classification perspective, these issues align with CWE-125 Out-of-bounds Read or Write for the boundary condition errors that facilitate sandbox escapes, and CWE-416 Use After Free for the memory corruption issue in the networking component. In terms of offensive security frameworks like MITRE ATT&CK, these vulnerabilities map to techniques involving Initial Access through browser exploitation (T1189) and Defense Evasion via Sandbox Escape (T1052), allowing attackers to bypass containment mechanisms designed to limit the blast radius of an initial compromise.
Mitigation strategies primarily involve immediate patching by updating Firefox or Firefox ESR to versions 158 and 153.5 respectively, which contain the necessary code fixes for both the boundary condition logic in site isolation and the memory management routines in the networking layer. For organizations managing large fleets of browsers, automated deployment tools should be utilized to ensure rapid rollout of these updates across all endpoints. Additionally, users are advised to keep their operating systems updated as a secondary defense line, since modern OS-level protections can sometimes mitigate the impact of successful exploitation attempts by restricting what an attacker can do even after gaining code execution privileges within the browser process.