CVE-2024-0751: Mozilla Firefox Privilege Escalation Flaw

CVE-2024-0751 Overview

CVE-2024-0751 is a privilege escalation vulnerability affecting Mozilla Firefox, Firefox ESR, and Thunderbird. A malicious devtools extension could be leveraged to escalate privileges beyond its intended scope, potentially allowing an attacker to gain elevated access to browser functionality and user data.

Critical Impact

A malicious browser extension exploiting the developer tools interface could escalate privileges, potentially compromising browser security boundaries and enabling unauthorized access to sensitive user data and browser capabilities.

Affected Products

• Mozilla Firefox (versions prior to 122)
• Mozilla Firefox ESR (versions prior to 115.7)
• Mozilla Thunderbird (versions prior to 115.7)
• Debian Linux 10.0

Discovery Timeline

• 2024-01-23 - CVE-2024-0751 published to NVD
• 2025-06-20 - Last updated in NVD database

Technical Details for CVE-2024-0751

Vulnerability Analysis

This vulnerability is classified under CWE-269 (Improper Privilege Management). The flaw resides in the browser's handling of developer tools extensions, where insufficient privilege checks allow a malicious extension to perform actions beyond its authorized scope.

The attack requires user interaction, specifically the installation or activation of a malicious devtools extension. Once installed, the extension can exploit the privilege management weakness to access protected browser functionality, manipulate browser security settings, or access data from other browser contexts that should be isolated.

This vulnerability affects the core privilege isolation mechanisms that normally restrict extension capabilities, making it particularly dangerous for users who install third-party developer tools extensions.

Root Cause

The root cause is improper privilege management (CWE-269) in the devtools extension API. The browser fails to adequately validate and restrict the actions that developer tools extensions can perform, allowing malicious extensions to bypass intended privilege boundaries. This design flaw enables extensions designed for debugging purposes to access elevated capabilities that should be reserved for the browser's core functionality.

Attack Vector

The attack is network-based and requires user interaction. An attacker would need to distribute a malicious devtools extension, either through social engineering to convince users to install it directly, or potentially through compromised extension distribution channels.

Once the victim installs the malicious extension, the exploitation occurs automatically through the flawed privilege management system. The extension can then escalate its privileges to achieve confidentiality, integrity, and availability impacts on the user's browser session and potentially their system.

The vulnerability mechanism involves the devtools extension exploiting weak privilege boundaries in the browser's extension API. When a devtools extension attempts to access protected browser functionality, the browser fails to properly validate whether the extension should have access to those capabilities, allowing the privilege escalation to succeed. For detailed technical information, see the Mozilla Bug Report #1865689.

Detection Methods for CVE-2024-0751

Indicators of Compromise

• Unexpected devtools extensions installed in Firefox, Firefox ESR, or Thunderbird that were not intentionally added by the user
• Browser extensions with unusually broad permissions or access to developer tools APIs
• Suspicious browser behavior indicating elevated extension activity, such as unauthorized access to browser settings or cross-origin data
• Unusual network traffic originating from browser extension processes

Detection Strategies

• Monitor browser extension installations and maintain an allowlist of approved developer tools extensions
• Implement endpoint detection and response (EDR) solutions to detect anomalous browser process behavior
• Review browser extension permissions regularly and flag extensions with devtools access capabilities
• Use browser security policies to restrict extension installation sources to trusted repositories only

Monitoring Recommendations

• Enable browser telemetry and security logging to capture extension installation and activation events
• Deploy network monitoring to detect unusual outbound traffic patterns from browser processes
• Implement user behavior analytics to identify when extensions access resources outside their expected scope
• Configure SIEM rules to alert on installation of developer tools extensions outside of authorized change windows

How to Mitigate CVE-2024-0751

Immediate Actions Required

• Update Mozilla Firefox to version 122 or later
• Update Mozilla Firefox ESR to version 115.7 or later
• Update Mozilla Thunderbird to version 115.7 or later
• Review and remove any suspicious or unnecessary devtools extensions
• Restrict extension installation permissions to trusted administrators only

Patch Information

Mozilla has released security patches addressing this vulnerability in Firefox 122, Firefox ESR 115.7, and Thunderbird 115.7. Organizations should prioritize updating to these versions or later. Detailed patch information is available in the Mozilla Security Advisory MFSA-2024-01, Mozilla Security Advisory MFSA-2024-02, and Mozilla Security Advisory MFSA-2024-04. Debian users should refer to the Debian LTS Announcement #15 and Debian LTS Announcement #22 for distribution-specific updates.

Workarounds

• Disable or remove all non-essential browser extensions, particularly those with devtools capabilities, until patching is complete
• Implement browser policies that restrict extension installation to administrator-approved sources only
• Use application whitelisting to prevent unauthorized browser extensions from loading
• Consider using browser isolation solutions to contain potential extension-based attacks

# Firefox policy configuration to restrict extensions
# Create or edit /etc/firefox/policies/policies.json (Linux)
# or deploy via Group Policy (Windows)
{
  "policies": {
    "ExtensionSettings": {
      "*": {
        "installation_mode": "blocked"
      }
    },
    "DisableDeveloperTools": true
  }
}