External risk intelligence

Firefox Enterprise Policies Mitigation Bypass Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.1)

CVE-2026-16390

This vulnerability affects enterprise policy enforcement mechanisms within a web browser. These components are client-side configurations managed internally by organizations and are not designed to be exposed to or reachable from the public internet.

Mozilla Firefox

before 140.13.0before 153.0.0141.0 to before 153.0

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A critical vulnerability has been identified in the Enterprise Policies component of Mozilla products, potentially allowing for the bypass of security mitigations. While specific products and versions are noted, the primary concern at this stage is to confirm the relevance and potential exposure of this issue within our environment.

Mitigation bypass in enterprise policies.
Leadership should remember if policies are affected.
Confirm relevance and potential exposure.

Attack Path

How an attacker could exploit the issue

An attacker could exploit a weakness in the Enterprise Policies component of the browser. This vulnerability, which doesn't require any special access or interaction from the user, could allow an attacker to bypass security measures related to enterprise policies. This could lead to unauthorized actions with significant consequences.

No privileges needed to start.
Triggered by policy manipulation.
Risks policy bypass and data compromise.

Live Threat

Current exploitation, exposure, and threat context

When supported by the advisory, this vulnerability could allow an attacker to bypass enterprise policy controls within the affected application. This could potentially lead to unauthorized modifications or the execution of actions that are otherwise restricted by organizational policies.

User-configured policies could be bypassed.
Bypass may occur via specially crafted web content.
Loss of policy enforcement.

Operational Fix

Recommended remediation, mitigation, and detection steps

Real-world ownership of this vulnerability likely falls to teams managing end-user computing, application deployment, or security policy enforcement. The initial step is to identify all deployed instances of the affected browser, confirm their network exposure, and assess business criticality. Once these factors are understood, the accountable owner can be identified to plan a risk-based remediation strategy, potentially involving coordination with the vendor.

Own by end-user computing or application teams.
Verify browser deployment and network exposure.
Plan remediation based on risk and vendor coordination.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is the Firefox Enterprise Policies component?

It is a framework within Mozilla Firefox that allows IT administrators to centrally manage browser settings and security configurations across an organization. These policies enforce rules for how the browser functions, such as restricting access to certain sites or managing add-ons, to ensure a standardized and secure computing environment for employees.

What does CVE-2026-16390 mean for security?

This CVE refers to a mitigation bypass, classified as CWE-693 (Protection Mechanism Failure). In plain terms, it means the security controls enforced by enterprise policies can be circumvented. Instead of the browser reliably following the rules set by your organization, an attacker could potentially override those restrictions to perform unauthorized actions.

How is this bypass triggered?

The vulnerability is triggered by manipulating the browser's policy enforcement mechanisms. It does not require a user to have special privileges or perform a specific action to initiate. Notably, it is not triggered by standard browser usage that complies with correctly applied policies; the vulnerability specifically exists within the engine's ability to resist interference with those configured rules.

Is this vulnerability a risk for my network?

According to Halo Surface Signal, this vulnerability is very unlikely to be reachable from the public internet. Because the affected enterprise policy components are client-side configurations managed internally, they are not designed to be exposed externally. The primary risk is limited to the specific end-user devices where these policies are enforced.

Do I need to take immediate action?

Your first step is to identify all instances of Firefox deployed in your environment. Confirm which devices are running versions prior to the fixed releases. Once identified, coordinate with the teams responsible for end-user computing or application deployment to plan an update cycle, as upgrading the browser is the standard method to resolve the policy enforcement defect.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.