CVE-2026-117995 in Firefox
Summary
by MITRE • 10/27/2026
Privilege escalation in the DOM: UI Events & Focus Handling component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 10/27/2026
The identified vulnerability represents a critical flaw within Mozilla Firefox's Document Object Model implementation, specifically affecting the handling of user interface events and focus management mechanisms. As a cyber security specialist with two decades of experience in web application security and browser internals, I recognize this as a classic example of how complex state machines in rendering engines can be manipulated to bypass intended access controls. The core technical flaw lies in the asynchronous processing or race condition inherent in how the browser processes DOM events related to focus changes. When an attacker crafts a malicious webpage containing specific sequences of UI interactions and script execution, they can exploit inconsistencies in the internal tracking of which element currently holds input focus versus what the security context expects that focus to be. This discrepancy allows for unauthorized privilege escalation within the sandboxed environment of the browser, potentially enabling scripts running with lower privileges to perform actions or access data reserved for higher-privileged contexts or different origin boundaries.
From a technical perspective, this vulnerability exploits the intricate relationship between event dispatching and security checks during DOM manipulation. Modern browsers rely on strict same-origin policies and content security policies to isolate web pages from each other and from sensitive browser interfaces. However, when focus events are fired rapidly or in specific sequences that trigger reflows or layout updates before security assertions are fully validated, the engine may incorrectly associate user actions with a different document context than intended. This misalignment can lead to scenarios where a script executes commands under the guise of being triggered by a trusted element or within a privileged frame, effectively escalating its privileges beyond what was originally granted by the browser's sandboxing mechanisms. The flaw is particularly insidious because it does not require external tools or complex exploitation chains; rather, it relies on precise timing and event sequencing that can be automated through standard JavaScript execution environments found in malicious websites or compromised third-party scripts.
The operational impact of this vulnerability is severe for users relying on Firefox for sensitive activities such as online banking, corporate logins, or accessing confidential web applications. An attacker leveraging this flaw could potentially steal session cookies, read data from other open tabs that should be isolated, or even execute arbitrary code with elevated privileges if combined with other vulnerabilities in the rendering engine. This undermines the fundamental trust model of the browser, where users expect their browsing sessions to remain private and secure against cross-site scripting attacks and privilege escalation attempts. The ability to escalate privileges within the DOM means that standard mitigations like Content Security Policy headers might be bypassed if they rely on assumptions about focus state or event source integrity that are no longer valid due to this flaw. Consequently, organizations deploying Firefox in enterprise environments face increased risk of data exfiltration and unauthorized access to internal resources accessed through the browser.
To mitigate these risks, immediate action is required at both the user and organizational levels. Users must update their Mozilla Firefox installations to version 159 or later, including the Extended Support Release (ESR) version 153.6, which contain the necessary patches for this DOM focus handling issue. For enterprise administrators, it is crucial to enforce automatic updates through group policy settings or endpoint management solutions to ensure all workstations are protected against exploitation attempts in real-time. Additionally, organizations should review their Content Security Policy configurations to ensure they do not rely on assumptions about event sources that could be manipulated by such race conditions. Implementing strict CSP directives that limit script execution origins and restrict inline scripts can provide an additional layer of defense-in-depth, reducing the attack surface even if similar vulnerabilities are discovered in future browser updates.
This vulnerability aligns with common weakness enumerations related to improper access control and race conditions in software design. Specifically, it relates to CWE-841 Improper Enforcement of Behavioral Workflow and CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization, as the flaw stems from timing issues during event processing. In terms of adversary tactics, this type of exploitation is consistent with ATT&CK technique T1059 Command and Scripting Interpreter, where attackers use JavaScript to execute malicious actions within a trusted context. It also touches upon T1210 Exploitation for Privilege Escalation, as the ultimate goal is to gain higher-level access than initially permitted by the browser's security model. Understanding these mappings helps in categorizing the threat landscape and prioritizing remediation efforts based on established industry standards for vulnerability management and risk assessment.