CVE-2026-74962 in Firefox
Summary
by MITRE • 08/18/2026
Site isolation issue in the Networking: Cookies component. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, and Firefox ESR 153.1.
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Analysis
by VulDB Data Team • 08/19/2026
The identified security flaw resides within the networking subsystem of Mozilla Firefox, specifically affecting the cookies management component responsible for handling site isolation policies. Site isolation is a critical browser security mechanism designed to prevent cross-site data leakage by ensuring that resources from different origins are processed in separate processes or contexts. When this isolation fails, it creates an environment where malicious websites may potentially access sensitive state information belonging to other sites with which the user has interacted. This vulnerability represents a breakdown in the enforcement of same-origin policies at the cookie storage layer, allowing for potential cross-site request forgery scenarios or unauthorized data exfiltration if combined with other attack vectors such as cross-site scripting.
The technical nature of this flaw involves an improper separation of cookie scopes during network requests and session management operations. In a properly isolated environment, cookies set by one origin should remain inaccessible to scripts running in another origin unless explicitly permitted through specific attributes like SameSite or Secure flags combined with proper domain matching logic. The defect likely stems from a race condition or logical error in how the browser associates incoming HTTP responses with their respective browsing contexts and process boundaries. This oversight allows data intended for strict isolation to be exposed across site boundaries, undermining the fundamental trust model of web applications that rely on cookies for session authentication and state persistence.
The operational impact of this vulnerability is significant as it compromises user privacy and account security. Attackers could potentially exploit this flaw to steal session tokens or tracking identifiers from high-value targets such as banking portals, email services, or enterprise dashboards. By bypassing site isolation restrictions, a malicious page loaded in one tab could read cookies set by another trusted domain if the victim navigates between them under specific conditions facilitated by the bug. This capability facilitates account takeover attacks and persistent surveillance of user activity across different web properties without requiring direct injection vulnerabilities like XSS within those target domains.
Mitigation strategies primarily involve updating to patched versions where these isolation checks have been rigorously enforced. Users must upgrade to Firefox version 154, Firefox Extended Support Release (ESR) version 140.14, or ESR version 153.1 immediately upon availability. These releases contain the necessary code corrections that restore strict boundaries between different site contexts during cookie processing operations. For organizations deploying Firefox at scale, it is imperative to automate patch management processes to ensure all endpoints receive these updates promptly. Additionally, administrators should enforce security headers such as Strict-Transport-Security and Content-Security-Policy across their own web applications to provide defense-in-depth measures that complement the browser's native protections against cross-site data leakage.
This issue aligns with Common Weakness Enumeration (CWE) category CWE-200, which covers Exposure of Sensitive Information to an Unauthorized Actor, as well as CWE-359 regarding Exposed Private Personal Information in Web Cookies. From a tactical perspective related to the MITRE ATT&CK framework for enterprise security, this vulnerability relates to techniques involving Collection via Browser Capture or Screen Capture and potentially Credential Access through Stealing Browser Credentials if session cookies are successfully exfiltrated. Understanding these mappings helps security teams prioritize remediation efforts based on the potential impact on confidentiality and integrity of user data within their specific threat landscape.