CVE-2026-16399 in Firefox
Summary
by MITRE • 07/21/2026
Site isolation issue in the DOM: Navigation component. This vulnerability was fixed in Firefox 153.
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Analysis
by VulDB Data Team • 07/21/2026
This vulnerability represents a critical site isolation breach within the Document Object Model navigation component of web browsers, specifically affecting Firefox versions prior to 153. The flaw stems from insufficient separation mechanisms between different websites or origins within the browser's rendering architecture, allowing malicious actors to potentially exploit cross-site scripting scenarios through manipulated navigation sequences. The issue fundamentally compromises the security boundaries that should exist between distinct web origins, creating pathways for unauthorized data access or execution across isolated sites.
The technical implementation of this vulnerability occurs at the DOM navigation layer where the browser's site isolation mechanisms fail to properly enforce origin-based security policies during navigation operations. When users navigate between different websites, the browser should maintain strict separation between memory spaces and security contexts, but this flaw allows for potential information leakage or code execution across these boundaries. The vulnerability manifests when the navigation component does not adequately validate or sanitize cross-origin navigation requests, potentially permitting malicious sites to access resources or data from other origins that they should not be permitted to reach.
The operational impact of this vulnerability extends beyond simple privacy concerns to encompass full system compromise potential within the browser environment. Attackers could leverage this flaw to perform cross-site scripting attacks, extract sensitive data from other websites, or execute arbitrary code in contexts where such access should be strictly prohibited. The severity increases when considering that modern web applications often handle sensitive user information, financial data, or personal identifiers that could be exposed through such isolation breaches. This vulnerability undermines the fundamental security model that browsers implement to protect users from malicious websites and cross-site attacks.
Mitigation strategies for this vulnerability require immediate patch application to Firefox versions prior to 153, as the fix addresses the core site isolation implementation within the DOM navigation component. Browser vendors should ensure that all navigation operations properly enforce origin-based security boundaries, implementing robust validation mechanisms that prevent unauthorized access across site isolation barriers. Organizations should conduct thorough security assessments of their browser deployment environments and verify that all instances have been updated to versions containing the necessary patches. The remediation process should also include monitoring for potential exploitation attempts and ensuring that user privileges are appropriately restricted to minimize the impact of any successful attacks.
This vulnerability aligns with common weakness enumerations such as CWE-284, which addresses improper access control mechanisms, and specifically relates to the broader category of site isolation failures in web browser security models. From an attack framework perspective, this issue maps to techniques described in the attack tactics and techniques framework where adversaries attempt to escalate privileges or bypass security controls through manipulation of core browser components. The fix implemented in Firefox 153 demonstrates proper remediation through enhanced navigation validation and strengthened origin enforcement mechanisms that prevent unauthorized cross-site access during navigation operations.