CVE-2025-9186: Mozilla Firefox Address Bar Spoofing Flaw

CVE-2025-9186 Overview

CVE-2025-9186 is an address bar spoofing vulnerability affecting the Firefox Focus browser for Android. The flaw resides in the Address Bar component and allows a malicious web page to manipulate the displayed URL. Attackers can leverage this behavior to present a trusted-looking origin while serving attacker-controlled content, enabling credible phishing scenarios on mobile devices. Mozilla addressed the issue in Firefox 142 and documented it in advisory MFSA-2025-64. The weakness is categorized as [CWE-451] (User Interface Misrepresentation of Critical Information).

Critical Impact
A remote attacker can spoof the address bar in Firefox Focus for Android, tricking users into trusting attacker-controlled content displayed under a legitimate URL.

Affected Products

Mozilla Firefox Focus for Android (prior to Firefox 142)
Mozilla Firefox for Android (Address Bar component)
Mozilla Firefox versions prior to 142

Discovery Timeline

2025-08-19 - CVE-2025-9186 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-9186

Vulnerability Analysis

CVE-2025-9186 is a user interface spoofing issue in the Address Bar component of Firefox Focus for Android. The browser renders a URL in the address bar that does not correspond to the actual origin of the loaded content. This mismatch between displayed identity and executing origin defeats the primary trust signal users rely on when evaluating web pages. The vulnerability requires user interaction, such as clicking a crafted link or visiting a malicious site, but does not require authentication.

Spoofing flaws of this class ([CWE-451]) are particularly impactful on mobile browsers because limited screen real estate already truncates URLs and hides security indicators. An attacker can pair the spoof with a phishing page that mimics banking, corporate SSO, or webmail portals. Mozilla resolved the issue in Firefox 142.

Root Cause

The root cause is improper handling of navigation or URL rendering logic within the Address Bar component. The browser updates or fails to update the displayed URL under specific navigation sequences, allowing an attacker-controlled page to appear as if it were served from a different origin. Full technical detail is tracked in Mozilla Bug Report #1445758.

Attack Vector

Exploitation occurs over the network. A user opens a malicious URL or is redirected to attacker infrastructure that triggers the spoofing sequence. The address bar then displays a URL of the attacker's choosing while the underlying page content is fully controlled by the adversary. The impact is scoped to integrity of information presented to the user; confidentiality and availability of the device are not directly affected.

No verified public proof-of-concept is available. Refer to the Mozilla Security Advisory MFSA-2025-64 for vendor-confirmed details.

Detection Methods for CVE-2025-9186

Indicators of Compromise

Mobile users reporting unexpected login prompts or credential requests on pages that appear to be trusted domains.
Outbound HTTP/HTTPS traffic from Android devices to newly registered domains immediately after clicking links from email, SMS, or messaging apps.
Firefox Focus for Android versions prior to 142 present on managed mobile endpoints.

Detection Strategies

Inventory installed browser versions across managed Android devices and flag any Firefox or Firefox Focus builds earlier than 142.
Correlate mobile web proxy or DNS logs with known phishing infrastructure and campaigns targeting mobile browsers.
Monitor identity provider logs for anomalous authentication attempts originating from Android user-agents shortly after link clicks.

Monitoring Recommendations

Enforce mobile device management (MDM) reporting for browser application versions and block outdated installs.
Integrate mobile browsing telemetry into the SIEM or data lake to surface repeated visits to look-alike domains.
Enable phishing-resistant multi-factor authentication so a successful spoof does not translate into account compromise.

How to Mitigate CVE-2025-9186

Immediate Actions Required

Update Firefox and Firefox Focus for Android to version 142 or later through the Google Play Store.
Push the updated browser through MDM to all managed Android devices and confirm installation through compliance reporting.
Notify users of the risk and instruct them to avoid entering credentials on pages reached through unsolicited links.

Patch Information

Mozilla fixed CVE-2025-9186 in Firefox 142. Details are published in Mozilla Security Advisory MFSA-2025-64 and tracked in Mozilla Bug Report #1445758. Users should install the latest release from the official Google Play Store listing to ensure the fix is applied.

Workarounds

Use an alternative up-to-date mobile browser until the Firefox Focus update can be deployed across the fleet.
Restrict click-through from untrusted sources by deploying mobile threat defense and URL filtering on managed devices.
Require phishing-resistant authentication (FIDO2, passkeys) so spoofed pages cannot harvest reusable credentials.

bash

# Verify installed Firefox package version on an Android device via ADB
adb shell dumpsys package org.mozilla.focus | grep versionName
adb shell dumpsys package org.mozilla.firefox | grep versionName

# Expected: versionName=142.0 or higher