CVE-2026-109750 in Firefox
Summary
by MITRE • 10/13/2026
Site isolation issue in the DOM: Web Authentication component. This vulnerability was fixed in Firefox 158.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 10/13/2026
The disclosed vulnerability represents a critical failure in the site isolation mechanisms within Mozilla Firefox, specifically affecting the implementation of the Web Authentication API. Site isolation is a fundamental security architecture designed to prevent cross-site data leakage by ensuring that resources from different origins are processed in separate processes or contexts. When this boundary is compromised, it creates an environment where malicious scripts hosted on one origin may potentially access sensitive state information belonging to another origin. In this specific instance, the flaw resides within the DOM bindings for Web Authentication, a standard used to provide strong authentication without passwords using public key cryptography. The vulnerability suggests that under certain conditions, the browser failed to properly segregate the context of authenticator requests or responses between different websites, thereby violating the principle of least privilege and origin isolation.
From a technical perspective, this issue likely stems from an improper handling of cross-origin frames or worker contexts when interacting with hardware-backed security keys or platform authenticators. The Web Authentication API allows web applications to register and authenticate users using public key cryptography instead of passwords. During these operations, the browser acts as an intermediary between the website and the user's device authentication mechanism. If site isolation is breached in this layer, a malicious webpage could potentially infer information about active sessions or authentication states on other sites that are open within the same browser profile. This could facilitate sophisticated cross-site request forgery attacks or allow for session hijacking scenarios where an attacker can determine if a specific user has authenticated to a target service without their direct interaction with that service's login page.
The operational impact of this vulnerability is significant, particularly in environments where users frequently access multiple sensitive web applications simultaneously. Attackers could exploit this flaw to perform timing attacks or side-channel analysis to deduce the presence of active sessions on high-value targets such as banking portals, email services, or enterprise identity providers. By correlating authentication events across different origins, an adversary might build a profile of user activity or identify specific accounts that are currently logged in. This undermines the trust model of the web and compromises the confidentiality of session tokens and authentication states. Although direct remote code execution is not implied by this site isolation breach, the ability to fingerprint active sessions poses a severe privacy risk and can serve as an initial vector for more targeted attacks against high-value targets.
Mitigation strategies primarily involve updating the browser software to version 158 or later, where these specific flaws in the Web Authentication component have been addressed. Users should ensure that automatic updates are enabled to receive security patches promptly. For organizations deploying Firefox across their workforce, it is advisable to enforce update policies through centralized management tools to guarantee compliance with the latest security standards. Additionally, users can mitigate residual risks by employing strict cookie and site data clearing practices after sessions end and utilizing browser extensions or settings that enhance isolation features where available. It is also recommended to monitor for any unusual behavior in authentication flows and report suspicious activity to security teams immediately.
This vulnerability aligns with CWE-200, which classifies information exposure vulnerabilities, as it allows an attacker to gain insights into system state through indirect means rather than direct data theft. Furthermore, the exploitation technique relates to ATT&CK tactic TA0043, specifically techniques involving reconnaissance and discovery within a browser environment. The breach of site isolation highlights the ongoing challenges in maintaining robust boundaries between web origins as browsers become increasingly complex application platforms. Addressing such issues requires continuous refinement of sandboxing architectures and rigorous testing of cross-origin interactions across all API implementations to ensure that security guarantees are not inadvertently weakened by implementation details.