CVE-2024-5687: Mozilla Firefox Auth Bypass Vulnerability

CVE-2024-5687 Overview

A security vulnerability exists in Firefox for Android where performing a specific sequence of actions when opening a new tab may result in an incorrect triggering principal being associated with that tab. The triggering principal is a critical security component used to calculate various security-sensitive values, including the Referer and Sec-* HTTP headers. This miscalculation creates potential for incorrect security checks within the browser and may cause incorrect or misleading information to be transmitted to remote websites.

Critical Impact

Improper access control in Firefox for Android's tab handling mechanism can lead to incorrect security header calculations, potentially bypassing browser security checks and sending misleading information to remote websites.

Affected Products

• Mozilla Firefox for Android versions prior to 127
• Firefox mobile browser on Android platforms
• Note: Desktop versions of Firefox are unaffected by this vulnerability

Discovery Timeline

• 2024-06-11 - CVE-2024-5687 published to NVD
• 2025-03-27 - Last updated in NVD database

Technical Details for CVE-2024-5687

Vulnerability Analysis

This vulnerability is classified as an Improper Access Control issue (CWE-284) affecting the triggering principal mechanism in Firefox for Android. The triggering principal is a fundamental security concept in the Firefox architecture that determines the security context and origin associated with a particular action or resource request.

When a user performs a specific sequence of actions while opening a new tab, the browser may incorrectly assign the triggering principal. This security context information is used throughout the browser to enforce same-origin policies and generate security-critical HTTP headers. The vulnerability specifically affects the calculation of:

• Referer headers: Which indicate the origin of the request
• Sec- headers*: Security headers including Sec-Fetch-Site, Sec-Fetch-Mode, Sec-Fetch-User, and Sec-Fetch-Dest that communicate request metadata to servers

The network-based attack vector allows remote exploitation without requiring user authentication or interaction beyond the initial tab-opening sequence.

Root Cause

The root cause stems from a race condition or logic error in the tab creation workflow specific to the Android implementation of Firefox. When new tabs are opened under certain conditions, the code responsible for establishing the triggering principal fails to correctly propagate the security context from the originating action to the newly created tab. This implementation flaw exists only in the Android codebase, leaving desktop versions unaffected.

The triggering principal should reflect the true origin that initiated the navigation, but due to this bug, it may reference an incorrect or unexpected principal, leading to security header miscalculations.

Attack Vector

An attacker could potentially exploit this vulnerability by crafting a malicious webpage that induces users to perform the specific sequence of actions required to trigger the bug. Once triggered, the incorrect principal association could lead to:

1. Security bypass scenarios: Where the browser's internal security checks use the wrong origin for policy decisions
2. Information leakage: Through improperly generated Referer headers that may expose browsing history or sensitive URLs to unintended third parties
3. CSRF-like attacks: Where the incorrect Sec-* headers may cause servers to misclassify the nature of requests

The vulnerability exploitation does not require authentication and can be performed over the network against any user running a vulnerable version of Firefox for Android. Technical details are available in Mozilla Bug Report #1889066.

Detection Methods for CVE-2024-5687

Indicators of Compromise

• Unusual or unexpected Referer headers in server logs that don't match expected navigation patterns
• Anomalous Sec-* header values in HTTP requests originating from Firefox for Android clients
• Reports from users experiencing unexpected cross-origin behavior in the mobile browser

Detection Strategies

• Monitor web server logs for HTTP requests with inconsistent or suspicious combinations of Referer and Sec-Fetch-* headers
• Implement server-side validation of security headers to detect potential exploitation attempts
• Use browser version fingerprinting in access logs to identify requests from vulnerable Firefox for Android versions

Monitoring Recommendations

• Enable detailed HTTP header logging on web servers to capture Referer and Sec-* header values
• Deploy web application firewall (WAF) rules to flag requests with suspicious header combinations
• Monitor for Mozilla security advisories and update browser deployments accordingly

How to Mitigate CVE-2024-5687

Immediate Actions Required

• Update Firefox for Android to version 127 or later immediately
• Verify browser version on all managed Android devices in your organization
• Implement Mobile Device Management (MDM) policies to enforce minimum browser versions
• Consider temporarily switching to alternative browsers on Android if immediate updates are not possible

Patch Information

Mozilla has addressed this vulnerability in Firefox version 127. The fix corrects the triggering principal assignment logic during tab creation on Android devices. Users should update through the Google Play Store or their preferred app distribution channel. For enterprise deployments, administrators should push the updated version through their MDM solution.

Detailed patch information is available in the Mozilla Security Advisory MFSA-2024-25.

Workarounds

• Avoid using the specific tab-opening action sequences until the browser is updated (exact sequences may vary)
• Use Firefox Focus or alternative Android browsers as temporary replacements
• Implement server-side validation of Referer and Sec-* headers to mitigate potential exploitation impact
• Enable automatic app updates on Android devices to ensure timely security patches

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

# Check for pending updates
adb shell am start -a android.intent.action.VIEW -d "market://details?id=org.mozilla.firefox"