CVE-2026-109708 in Firefox
Summary
by MITRE • 10/13/2026
Sandbox escape due to incorrect boundary conditions 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 • 10/13/2026
The identified security flaw resides within the networking subsystem of Mozilla Firefox, specifically involving a critical failure in boundary condition validation during sandbox isolation processes. In modern web browsers, the rendering engine operates multiple content processes within isolated sandboxes to prevent malicious code from accessing sensitive system resources or other browser components. This particular vulnerability arises when the application fails to correctly enforce memory boundaries or state checks associated with network requests and responses. An attacker could exploit this logic error by crafting a specially designed webpage that triggers an incorrect boundary condition, thereby bypassing the intended sandbox restrictions.
This type of flaw is categorized under CWE-20 Improper Input Validation, as it stems from insufficient checking of data inputs against expected constraints before processing. Furthermore, it aligns with MITRE ATT&CK technique T1615, which covers Software Exploitation for Privilege Escalation or Scope Expansion. By escaping the sandbox, an attacker gains a higher level of access than intended by the browser's security model. This escalation allows potential execution of arbitrary code within the context of the parent process or other restricted environments, significantly increasing the severity of the impact beyond typical cross-site scripting or data theft scenarios.
The operational impact of this vulnerability is severe because it undermines one of the primary defense mechanisms against web-based attacks. Successful exploitation could lead to remote code execution on the victim's machine, allowing full control over the affected system depending on user privileges. It also poses a risk to session hijacking and sensitive data exfiltration if the attacker can access cookies or local storage from other tabs that should remain isolated due to sandboxing failures. The lack of proper boundary checks means that malformed network packets or manipulated HTTP headers could trigger undefined behavior, leading to memory corruption or logic bypasses that compromise browser integrity.
To mitigate this risk, users must ensure they are running the patched versions of Firefox, specifically version 158 for standard releases and version 153.5 for Extended Support Release channels. These updates contain code changes that enforce stricter boundary checks within the networking component, ensuring that all inputs are validated against expected limits before processing. Organizations should implement automated patch management systems to deploy these fixes promptly across all endpoints. Additionally, enabling automatic security update notifications ensures that administrators and end-users are alerted immediately when new patches become available, reducing the window of exposure to such critical vulnerabilities.