CVE-2024-8381: Mozilla Firefox Type Confusion Vulnerability

CVE-2024-8381 Overview

CVE-2024-8381 is a type confusion vulnerability discovered in Mozilla Firefox and Firefox ESR that can be triggered when looking up a property name on an object being used as the with environment in JavaScript. This vulnerability exists in the browser's JavaScript engine and could potentially be exploited by attackers to achieve arbitrary code execution through specially crafted web content.

Critical Impact

This type confusion vulnerability could allow remote attackers to execute arbitrary code on affected systems simply by convincing users to visit a malicious website. No authentication or user interaction beyond browsing is required for exploitation.

Affected Products

• Mozilla Firefox versions prior to 130
• Mozilla Firefox ESR versions prior to 128.2
• Mozilla Firefox ESR versions prior to 115.15
• Mozilla Thunderbird versions prior to 128.2
• Mozilla Thunderbird versions prior to 115.15

Discovery Timeline

• September 3, 2024 - CVE-2024-8381 published to NVD
• November 4, 2025 - Last updated in NVD database

Technical Details for CVE-2024-8381

Vulnerability Analysis

This vulnerability is classified as CWE-843 (Access of Resource Using Incompatible Type, commonly known as Type Confusion). Type confusion vulnerabilities occur when a program allocates or initializes a resource such as an object using one type, but later accesses that resource using an incompatible type. In the context of this Firefox vulnerability, the issue arises specifically within the JavaScript engine when handling property lookups on objects used in with statement environments.

The with statement in JavaScript extends the scope chain for a statement, adding the given object to the head of the scope chain during evaluation. When the JavaScript engine performs property lookups within this extended scope, a type confusion can occur due to improper type handling of the environment object. This can lead to memory corruption, potentially allowing attackers to manipulate program execution flow.

Root Cause

The root cause of CVE-2024-8381 lies in the JavaScript engine's handling of property name lookups when an object is used as the with environment. During the scope chain resolution process, the engine fails to properly validate or handle type information, leading to a type confusion condition. This occurs because the code path responsible for resolving properties in the with environment context does not adequately verify that the object type matches what is expected during subsequent operations. Technical details are available in the Mozilla Bug Report #1912715.

Attack Vector

The attack vector for CVE-2024-8381 is network-based, requiring no privileges or user authentication. An attacker could exploit this vulnerability by:

1. Creating a malicious web page containing specially crafted JavaScript code that utilizes the with statement in a way that triggers the type confusion
2. Hosting this content on an attacker-controlled website or injecting it into compromised legitimate websites
3. Luring victims to visit the malicious page through phishing emails, social engineering, or malicious advertisements
4. Upon page load, the malicious JavaScript executes in the browser context, triggering the type confusion and potentially achieving code execution

The vulnerability requires no user interaction beyond visiting the malicious page, making it particularly dangerous for drive-by attack scenarios.

Detection Methods for CVE-2024-8381

Indicators of Compromise

• Unusual JavaScript execution patterns involving heavy use of with statements in browser processes
• Unexpected memory access violations or crashes in Firefox/Thunderbird processes
• Abnormal browser process behavior including unexpected child process spawning
• Memory corruption signatures in browser crash reports

Detection Strategies

• Monitor browser process memory for signs of type confusion exploitation, including unexpected object type transitions
• Deploy endpoint detection solutions capable of identifying JavaScript engine exploitation attempts
• Implement network monitoring to detect connections to known malicious domains serving exploit code
• Enable browser crash reporting and analyze crash dumps for exploitation signatures

Monitoring Recommendations

• Enable Mozilla's crash reporting feature to capture exploitation attempts
• Monitor endpoint security logs for Firefox/Thunderbird process anomalies
• Implement web proxy logging to track browsing activity and identify potential exposure to malicious sites
• Deploy SentinelOne agents with behavioral AI to detect memory corruption exploitation in real-time

How to Mitigate CVE-2024-8381

Immediate Actions Required

• Update Mozilla Firefox to version 130 or later immediately
• Update Firefox ESR to version 128.2 or 115.15 depending on your ESR track
• Update Mozilla Thunderbird to version 128.2 or 115.15 depending on your release track
• Verify updates have been applied across all organizational endpoints
• Consider temporarily blocking access to untrusted websites until patching is complete

Patch Information

Mozilla has released security patches addressing this vulnerability. Organizations should apply the following updates:

• Firefox: Update to version 130 or later - MFSA-2024-39
• Firefox ESR 128.x: Update to version 128.2 or later - MFSA-2024-40
• Firefox ESR 115.x: Update to version 115.15 or later - MFSA-2024-41
• Thunderbird 128.x: Update to version 128.2 or later - MFSA-2024-43
• Thunderbird 115.x: Update to version 115.15 or later - MFSA-2024-44

Debian users should also apply updates per Debian LTS Announcement #12 and Debian LTS Announcement #25.

Workarounds

• Disable JavaScript in Firefox via about:config by setting javascript.enabled to false (note: this will break most websites)
• Use network security controls to block access to untrusted or suspicious websites
• Implement browser isolation solutions to contain potential exploitation attempts
• Consider using alternative browsers until patches can be applied in high-risk environments

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

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

# Update Firefox on RHEL/CentOS systems
sudo yum update firefox