CVE-2026-109766 in Firefox
Summary
by MITRE • 10/13/2026
Mitigation bypass in the Enterprise Policies component. This vulnerability was fixed in Firefox 158 and Firefox ESR 153.5.
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Analysis
by VulDB Data Team • 10/13/2026
The identified vulnerability represents a critical failure within the enterprise policy enforcement mechanisms of Mozilla Firefox, specifically affecting versions prior to 158 for standard releases and prior to 153.5 for Extended Support Release channels. This flaw allows attackers or malicious actors with local access to bypass security configurations that are intended to be immutable by end-users. In corporate environments, administrators rely on these enterprise policies to enforce strict security postures, such as disabling specific browser features, restricting add-on installations, or mandating secure connection protocols. The ability to circumvent these controls undermines the fundamental premise of centralized device management and exposes organizational assets to unnecessary risk.
From a technical perspective, this issue likely stems from an improper validation check within the policy engine that fails to correctly distinguish between user-initiated actions and system-level enforcement rules. When such a bypass exists, it typically allows for the modification or removal of restricted settings through standard browser interfaces or configuration files that should have been locked down by administrative policies. This type of flaw is characteristic of logic errors where the application does not consistently apply security constraints across all code paths involved in policy evaluation and execution. The vulnerability effectively neutralizes the protective measures put in place to prevent unauthorized changes, allowing for potential privilege escalation at the browser level or facilitating further attacks that rely on a compromised browsing environment.
The operational impact of this vulnerability is significant for organizations utilizing Firefox as their primary web browser under managed device policies. Attackers who exploit this flaw can disable security features such as phishing and malware protection, remove content blockers, or enable insecure protocols like HTTP instead of HTTPS. This creates an attack surface where users are no longer protected by the organization's defined security baseline. Furthermore, it may allow for the installation of malicious extensions that were previously prohibited, leading to data exfiltration, session hijacking, or credential theft. The breach of trust in enterprise configurations can also lead to compliance violations if specific regulatory standards require strict adherence to browser hardening guidelines.
This vulnerability aligns with CWE-250, which describes execution with unnecessary privileges, and more specifically relates to CWE-693, Protection Mechanism Failure, where the system fails to protect resources from unauthorized access or modification. In terms of offensive security frameworks, this flaw facilitates techniques associated with MITRE ATT&CK T1548.002, Abuse Configuration: Disable or Modify System Process, as it allows for the alteration of security settings that are meant to be persistent and enforced by administrators. It also touches upon aspects of lateral movement if the compromised browser is used to access internal resources without proper authentication controls being active due to policy bypass.
To mitigate this risk, organizations must immediately update all Firefox installations to version 158 or later for standard releases, or version 153.5 and later for ESR channels. It is imperative that patch management processes are accelerated to ensure these updates are deployed across all endpoints within the enterprise environment. Additionally, administrators should verify the integrity of their policy configurations after updating, as previous attempts to exploit this vulnerability may have left residual changes in local configuration files. Regular auditing of browser settings against the intended security baseline can help detect any unauthorized modifications that occurred prior to remediation. Monitoring for unusual browser behavior or unexpected changes in extension lists serves as an effective detection mechanism while patching efforts are underway.