CVE-2026-2800: Mozilla Firefox Auth Bypass Vulnerability

CVE-2026-2800 Overview

CVE-2026-2800 is a spoofing vulnerability affecting the WebAuthn component in Firefox for Android. This security flaw allows attackers to potentially bypass authentication mechanisms by exploiting weaknesses in the WebAuthn implementation, which is responsible for handling passwordless authentication and multi-factor authentication using security keys and biometrics on Android devices.

Critical Impact

This vulnerability could allow attackers to spoof WebAuthn authentication requests, potentially enabling unauthorized access to accounts protected by FIDO2/WebAuthn credentials on affected Mozilla products.

Affected Products

• Mozilla Firefox versions prior to 148
• Mozilla Thunderbird versions prior to 148
• Firefox for Android with WebAuthn functionality enabled

Discovery Timeline

• 2026-02-24 - CVE-2026-2800 published to NVD
• 2026-02-26 - Last updated in NVD database

Technical Details for CVE-2026-2800

Vulnerability Analysis

This vulnerability is classified under CWE-290 (Authentication Bypass by Spoofing), indicating a fundamental weakness in how the WebAuthn component validates authentication requests. The WebAuthn API is designed to provide strong, phishing-resistant authentication by binding credentials to specific origins and verifying the authenticity of authentication requests through cryptographic challenges.

The spoofing issue in Firefox for Android allows attackers to circumvent these protections. When a malicious actor crafts specially designed authentication requests, the WebAuthn component fails to properly validate the origin or the integrity of the request, enabling authentication bypass scenarios. This is particularly dangerous because WebAuthn is often used as a security-enhancing measure for sensitive accounts.

Root Cause

The root cause stems from insufficient validation in the WebAuthn component's request handling logic on Android. The implementation fails to properly verify the authenticity of authentication ceremonies, allowing spoofed requests to be processed as legitimate. This weakness in the authentication flow enables attackers to bypass the security guarantees that WebAuthn is designed to provide.

Attack Vector

The attack can be conducted over the network without requiring any privileges or user interaction. An attacker could exploit this vulnerability through several vectors:

1. Malicious Web Pages: A compromised or malicious website could initiate spoofed WebAuthn requests that appear to originate from a legitimate service
2. Man-in-the-Middle Scenarios: Attackers positioned between the user and the legitimate service could intercept and modify WebAuthn flows
3. Phishing Attacks: While WebAuthn is designed to prevent phishing, this spoofing vulnerability could be leveraged to defeat those protections

The vulnerability can be exploited remotely, making it accessible to a wide range of threat actors. The mechanism involves manipulating the WebAuthn authentication flow to bypass credential verification, potentially allowing attackers to authenticate as legitimate users without possessing the required security keys or biometric credentials.

Detection Methods for CVE-2026-2800

Indicators of Compromise

• Unusual WebAuthn authentication requests from unexpected origins in browser logs
• Authentication events for accounts that correlate with suspicious network activity
• Browser crash reports or errors related to WebAuthn component failures
• Anomalous credential usage patterns that don't match legitimate user behavior

Detection Strategies

• Monitor browser version deployments across the organization to identify unpatched Firefox and Thunderbird installations below version 148
• Implement network-level monitoring for suspicious WebAuthn-related traffic patterns
• Review authentication logs for failed or anomalous WebAuthn ceremonies
• Deploy endpoint detection solutions capable of identifying exploitation attempts targeting browser vulnerabilities

Monitoring Recommendations

• Enable enhanced logging for WebAuthn authentication events on critical applications
• Correlate browser activity with authentication server logs to identify spoofing attempts
• Monitor for indicators of credential compromise on accounts using WebAuthn
• Track Mozilla security advisories and apply patches promptly as they become available

How to Mitigate CVE-2026-2800

Immediate Actions Required

• Update Firefox to version 148 or later immediately on all Android devices
• Update Thunderbird to version 148 or later on affected systems
• Consider temporarily disabling WebAuthn functionality for high-risk applications until patches can be deployed
• Implement additional authentication factors as a compensating control where feasible

Patch Information

Mozilla has released security patches addressing this vulnerability. Detailed information is available in the official security advisories:

• Mozilla Security Advisory MFSA-2026-13
• Mozilla Security Advisory MFSA-2026-16

Technical details about the bug can be found in Mozilla Bug Report #1988145.

Organizations should prioritize updating to Firefox 148 and Thunderbird 148 to remediate this vulnerability.

Workarounds

• Disable WebAuthn functionality in Firefox for Android until the patch can be applied by navigating to about:config and setting security.webauth.webauthn to false
• Use alternative browsers on Android devices for sensitive authentication workflows until Firefox is updated
• Implement server-side rate limiting and anomaly detection for WebAuthn authentication requests
• Consider using hardware security keys with additional PIN protection as an extra layer of defense

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

# Check Thunderbird version
thunderbird --version

# Ensure automatic updates are enabled in Firefox
# Navigate to: Settings > About Firefox > Check for updates