CVE-2026-100804 in Firefox
Summary
by MITRE • 09/29/2026
Sandbox escape due to use-after-free in the Preferences: Backend component. This vulnerability was fixed in Firefox 157.
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Analysis
by VulDB Data Team • 09/29/2026
The identified security flaw resides within the Preferences backend subsystem of Mozilla Firefox, specifically manifesting as a use-after-free condition that facilitates sandbox escape. A use-after-free vulnerability occurs when software continues to reference a memory block after it has been deallocated and potentially reallocated for other purposes. In this specific context, the defect allows an attacker who successfully exploits this flaw within the browser's rendering or preference handling engine to execute arbitrary code with elevated privileges outside of the restricted sandbox environment that normally isolates web content from the host operating system. This represents a critical escalation of privilege where the boundary between untrusted web content and trusted local resources is breached, allowing malicious scripts or remote attackers to interact directly with underlying system components without restriction.
From a technical perspective, this vulnerability highlights a failure in memory management protocols within the backend logic that processes user preferences. When an object representing preference data is freed from memory but retains active pointers held by other parts of the application, subsequent access to those dangling pointers can lead to unpredictable behavior. In modern browser architectures, such as Firefox's multi-process model, strict sandboxing is employed to limit the damage caused by web-based attacks. By exploiting a use-after-free in the backend component, an attacker bypasses these isolation mechanisms. The exploit likely involves crafting specific inputs that trigger the premature deallocation of critical objects while maintaining references to them, thereby gaining control over memory layout and executing arbitrary instructions within the context of the browser process or potentially higher-privileged processes depending on the exact implementation details of the sandbox escape vector.
The operational impact of this vulnerability is severe due to its potential for remote code execution and privilege escalation. An attacker could host a malicious webpage designed to trigger this flaw when visited by an unsuspecting user. Upon successful exploitation, the attacker gains the ability to execute arbitrary commands on the victim's machine with the same privileges as the browser process. This can lead to full system compromise, including data theft, installation of persistent malware, or use of the compromised device for further attacks in a networked environment. The severity is compounded by the fact that sandbox escapes are among the most dangerous classes of vulnerabilities because they negate the primary defense mechanism browsers employ against web-based threats.
This vulnerability aligns with Common Weakness Enumeration (CWE) identifier CWE-416, which describes use-after-free conditions where a pointer references memory that has been freed or is no longer valid. Furthermore, in terms of offensive security tactics, this exploit path corresponds to MITRE ATT&CK technique T1059, specifically command and script interpretation within the context of execution after initial access. The bypass of sandbox controls also relates to techniques involving privilege escalation and defense evasion, as it allows malicious code to operate outside monitored or restricted environments.
To mitigate the risks associated with this vulnerability, immediate action is required to update the browser software. Mozilla has addressed this issue in Firefox version 157 by correcting the memory management logic within the Preferences backend component. Users should ensure their browsers are updated to this latest stable release as soon as possible. Additionally, organizations relying on Firefox for enterprise environments should verify that deployment pipelines include automatic updates or manual patching procedures to maintain compliance with security baselines. While waiting for updates, users can employ additional layers of defense such as disabling JavaScript in untrusted sites using browser extensions or configuring strict content security policies if feasible within their specific use cases, although these are not substitutes for the underlying code fix provided by the vendor.