CVE-2026-117861 in Firefox
Summary
by MITRE • 10/27/2026
Sandbox escape in the DOM: Navigation component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 10/28/2026
The identified vulnerability represents a critical security flaw within the Document Object Model navigation components of Mozilla Firefox, specifically classified as a sandbox escape mechanism. In modern web browsers, the rendering engine operates with multiple process isolation levels to contain potential exploits from affecting the host operating system or other browser processes. The DOM navigation subsystem is responsible for handling URL changes and frame transitions, which are high-privilege operations that require strict validation of input sources and destination contexts. When this component fails to properly enforce these boundaries, it allows malicious web content to bypass expected security constraints, effectively breaking out of the restricted sandbox environment where untrusted scripts typically execute.
This type of vulnerability is fundamentally rooted in improper access control mechanisms within the browser's internal architecture. Attackers can craft specific HTML or JavaScript payloads that exploit race conditions or logic errors during navigation events to trick the engine into granting elevated privileges to content that should remain confined. By leveraging this flaw, a remote attacker could potentially execute arbitrary code with higher system-level permissions than intended by the sandbox policy. This undermines the core security model of the browser, which relies on process isolation and privilege separation to mitigate the impact of zero-day exploits found in other components such as JavaScript engines or rendering parsers.
The operational impact of this vulnerability is severe for end-users who visit maliciously crafted websites. Successful exploitation could allow an attacker to read sensitive data from other tabs or windows that are normally isolated, modify browser settings without user consent, or install persistent malware on the victim's machine by leveraging the elevated privileges gained through the sandbox escape. This transforms a typical cross-site scripting scenario into a full system compromise vector, significantly increasing the risk profile for users browsing untrusted content. The vulnerability affects both standard releases and extended support versions prior to their respective patches, indicating that legacy systems or those with delayed update cycles are particularly at risk.
To mitigate this threat, organizations must ensure that all instances of Firefox are updated to version 159 for standard distributions or version 153.6 for Extended Support Release channels immediately upon availability. This patch includes the necessary code corrections to enforce stricter validation checks within the navigation component and reinforce sandbox boundaries. In environments where immediate patching is not feasible, network-level controls such as web filtering proxies can be configured to block access to known malicious domains or restrict certain types of dynamic content execution that might trigger this specific flaw. Additionally, enabling strict Content Security Policy headers on internal applications reduces the attack surface by limiting which scripts are allowed to interact with navigation APIs.
From a classification perspective, this issue aligns closely with CWE-284 Improper Access Control and CWE-755: Improper Handling of Exceptional Conditions within web application frameworks or browser engines. It also maps to MITRE ATT&CK techniques related to Defense Evasion and Privilege Escalation, specifically the use of client-side sandbox escapes to bypass security software restrictions. Understanding these mappings helps security teams prioritize remediation efforts based on industry-standard risk assessments rather than relying solely on vendor severity ratings. Continuous monitoring for anomalous browser behavior and keeping endpoint detection systems updated with signatures targeting known exploitation patterns can provide an additional layer of defense against this specific class of vulnerabilities.