CVE-2026-16375 in Firefox
Summary
by MITRE • 07/21/2026
Site isolation issue in the Networking: HTTP component. This vulnerability was fixed in Firefox 153 and Firefox ESR 140.13.
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Analysis
by VulDB Data Team • 07/21/2026
The vulnerability under discussion represents a site isolation issue within the networking http component of firefox browser architecture. This type of flaw fundamentally compromises the security boundaries that separate different websites and their respective data when multiple tabs or windows are open simultaneously. The issue stems from insufficient isolation mechanisms that allow malicious websites to potentially access or manipulate data from other sites running in separate browser contexts, creating a serious cross-site scripting scenario that undermines the fundamental security model of modern web browsers.
The technical implementation flaw occurs within the http networking stack where requests and responses from different origins are not properly segregated during processing. This allows for potential information leakage between sites, particularly when dealing with shared resources, cookies, or cached data that should remain isolated. The vulnerability specifically affects how firefox handles network communications between different domains, creating pathways through which malicious actors could exploit the lack of proper boundary enforcement in the http component. Such issues typically arise from inadequate validation of origin headers, insufficient sandboxing of network operations, or flawed memory management when handling cross-origin requests.
The operational impact of this site isolation weakness extends beyond simple data exposure to encompass potential full system compromise scenarios. An attacker could leverage this vulnerability to execute cross-site scripting attacks, steal session cookies, access sensitive user information from other tabs, or even perform more sophisticated attacks like credential theft across different domains. The severity increases significantly when users maintain multiple browser sessions or have active connections to multiple sites simultaneously, as the attack surface expands exponentially. This type of vulnerability directly impacts user privacy and data integrity, potentially allowing unauthorized access to personal information, financial data, or corporate secrets depending on the nature of the websites being accessed.
Mitigation strategies for this vulnerability involve immediate deployment of the security patches released in firefox version 153 and firefox esr 140.13, which implement proper isolation mechanisms within the http networking component. Organizations should ensure all users upgrade to these versions promptly and conduct thorough testing to verify that network operations function correctly after patching. Additional protective measures include implementing strict content security policies, enabling browser security features like strict site isolation, and monitoring for unusual network activity patterns that might indicate exploitation attempts. This vulnerability aligns with cwe-1203 which addresses improper isolation of security-relevant resources, and relates to attack techniques in the attacker framework that target browser sandboxing mechanisms. Regular security audits of browser configurations and network stack implementations should be conducted to identify similar isolation weaknesses before they can be exploited by malicious actors.