CVE-2024-5699: Mozilla Firefox Cookie Prefix Vulnerability

CVE-2024-5699 Overview

A critical vulnerability has been identified in Mozilla Firefox where cookie prefixes such as __Secure and __Host were being checked using case-sensitive comparison instead of case-insensitive comparison as required by the specification. This implementation flaw allows attackers to bypass cookie security attributes by using incorrectly capitalized prefixes, potentially undermining the browser's cookie security model.

Critical Impact

This vulnerability allows attackers to bypass cookie prefix security controls, potentially enabling session hijacking, credential theft, and other attacks that the __Secure and __Host prefixes are specifically designed to prevent.

Affected Products

• Mozilla Firefox versions prior to 127

Discovery Timeline

• 2024-06-11 - CVE-2024-5699 published to NVD
• 2025-04-04 - Last updated in NVD database

Technical Details for CVE-2024-5699

Vulnerability Analysis

This vulnerability is categorized under CWE-178 (Improper Handling of Case Sensitivity), representing a fundamental implementation error in Firefox's cookie parsing logic. The browser specification mandates that cookie prefixes like __Secure- and __Host- must be evaluated using case-insensitive string comparison to ensure consistent security enforcement regardless of capitalization variations.

When Firefox performs case-sensitive checks instead, an attacker can craft cookies with alternative capitalizations (e.g., __SECURE-, __secure-, or __SeCuRe-) that would bypass the security restrictions normally enforced by these prefixes. This breaks the security contract that web applications rely upon when using these prefixes to protect sensitive cookies.

Root Cause

The root cause lies in Firefox's cookie parsing implementation where string comparison operations for cookie prefixes were performed using case-sensitive matching. According to RFC 6265bis and the browser specification, cookie prefix checks should be case-insensitive to ensure robust security enforcement. The implementation in affected versions of Firefox failed to adhere to this requirement, creating a security gap that could be exploited to circumvent cookie security attributes.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker operating in a network position (such as through a man-in-the-middle attack, malicious website, or compromised HTTP connection) could set cookies with incorrectly capitalized prefixes. Since Firefox would not recognize these as secure cookies requiring special handling, the browser would accept them without enforcing the security constraints that the prefixes are meant to provide.

For example, a __SECURE-session cookie might be set without requiring a secure (HTTPS) connection, or a __HOST-csrf cookie might be set without the proper domain and path restrictions, effectively bypassing the protections these prefixes are designed to enforce.

Detection Methods for CVE-2024-5699

Indicators of Compromise

• Presence of cookies with non-standard capitalization of security prefixes (e.g., __SECURE-, __secure-, __HOST-)
• Session cookies being set over non-HTTPS connections that should be protected
• Unexpected cookie behavior in web applications relying on prefix-based security
• Anomalous authentication or session management activity

Detection Strategies

• Monitor web server logs for cookies with unusual prefix capitalizations that deviate from standard __Secure- or __Host- patterns
• Implement browser version detection to identify vulnerable Firefox installations within the organization
• Review web application firewall (WAF) logs for cookie manipulation attempts
• Deploy endpoint detection solutions that can identify outdated browser versions

Monitoring Recommendations

• Establish browser version inventory and monitor for vulnerable Firefox installations
• Configure network monitoring to detect cookie-based attack patterns
• Enable detailed logging on web applications that rely on cookie prefix security
• Set up alerts for detection of cookies with non-standard capitalization patterns

How to Mitigate CVE-2024-5699

Immediate Actions Required

• Update Mozilla Firefox to version 127 or later immediately
• Enable automatic updates for Firefox to receive future security patches
• Verify web applications are using HTTPS and implementing additional server-side cookie validation
• Consider implementing HTTP Strict Transport Security (HSTS) to reduce attack surface

Patch Information

Mozilla has addressed this vulnerability in Firefox version 127. Users and organizations should update to this version or later to remediate the issue. Detailed patch information is available in the Mozilla Security Advisory MFSA-2024-25. Additional technical details can be found in Mozilla Bug Report #1891349.

Workarounds

• Deploy enterprise browser management policies to enforce Firefox updates
• Implement server-side validation of cookie security attributes independent of browser prefix handling
• Use Content Security Policy (CSP) headers to provide additional security layers
• Consider using alternative browsers while awaiting Firefox updates in critical environments

# Verify Firefox version on Linux/macOS
firefox --version

# Update Firefox on Debian/Ubuntu systems
sudo apt update && sudo apt upgrade firefox

# Update Firefox on Fedora/RHEL systems
sudo dnf update firefox