CVE-2025-14324: Mozilla Firefox JIT RCE Vulnerability

CVE-2025-14324 Overview

CVE-2025-14324 is a critical JIT miscompilation vulnerability in the JavaScript Engine's Just-In-Time (JIT) compilation component affecting Mozilla Firefox and Thunderbird. The vulnerability arises from improper code generation during JIT compilation, which can lead to code injection attacks. This flaw enables remote attackers to potentially execute arbitrary code by crafting malicious JavaScript that triggers the miscompilation behavior.

Critical Impact

This JIT miscompilation vulnerability can be exploited remotely via malicious web content, potentially allowing attackers to execute arbitrary code with the privileges of the browser user. No authentication or user interaction is required for exploitation.

Affected Products

• Mozilla Firefox < 146
• Mozilla Firefox ESR < 115.31
• Mozilla Firefox ESR < 140.6
• Mozilla Thunderbird < 146
• Mozilla Thunderbird ESR < 140.6

Discovery Timeline

• December 9, 2025 - CVE-2025-14324 published to NVD
• December 11, 2025 - Last updated in NVD database

Technical Details for CVE-2025-14324

Vulnerability Analysis

This vulnerability stems from a miscompilation error in the SpiderMonkey JavaScript engine's JIT compiler. JIT compilation optimizes frequently executed JavaScript code by translating it into native machine code at runtime. When the JIT compiler incorrectly handles certain code patterns, it can generate machine code that deviates from the expected behavior of the original JavaScript, leading to type confusion or memory corruption scenarios.

The CWE-94 (Improper Control of Generation of Code) classification indicates that the vulnerability allows an attacker to influence the code generation process in ways that can lead to arbitrary code execution. In the context of browser JIT engines, this type of flaw is particularly dangerous as it can be triggered simply by visiting a malicious webpage.

Root Cause

The root cause of CVE-2025-14324 lies in the JIT compilation pipeline's handling of specific JavaScript constructs. During optimization passes, the compiler makes assumptions about variable types or code paths that may not hold true in all cases. When these assumptions are violated at runtime, the generated native code operates on incorrect data types or memory regions, creating an exploitable condition.

JIT miscompilation vulnerabilities typically occur in edge cases involving:

• Type speculation failures during optimization
• Incorrect bounds check elimination
• Improper handling of prototype chain modifications
• Race conditions in multi-threaded compilation scenarios

Attack Vector

The attack vector for this vulnerability is network-based and requires no user interaction or authentication. An attacker can exploit this vulnerability by:

1. Crafting malicious JavaScript code designed to trigger the specific miscompilation pattern
2. Hosting the malicious code on a web server or injecting it into a compromised website
3. Waiting for victims to visit the malicious or compromised site using a vulnerable version of Firefox or Thunderbird
4. The browser's JIT compiler processes the malicious JavaScript, generating incorrect machine code
5. Execution of the miscompiled code leads to memory corruption or code injection

For Thunderbird, the attack surface extends to HTML emails with embedded JavaScript, though Thunderbird's default security settings typically restrict JavaScript execution in email content.

Technical details regarding the specific exploitation mechanism can be found in the Mozilla Bug Report #1996840.

Detection Methods for CVE-2025-14324

Indicators of Compromise

• Unexpected browser crashes or hangs, particularly when visiting untrusted websites
• Abnormal memory consumption patterns in Firefox or Thunderbird processes
• Suspicious child process spawning from browser processes
• Unusual network connections originating from browser processes to unknown external hosts

Detection Strategies

• Monitor for crash reports in Firefox/Thunderbird that reference SpiderMonkey JIT components
• Implement network-level detection for known malicious JavaScript patterns associated with JIT exploitation
• Deploy endpoint detection and response (EDR) solutions capable of identifying anomalous browser behavior
• Review browser telemetry data for unusual JIT compilation events or optimization bailouts

Monitoring Recommendations

• Enable enhanced crash reporting in Firefox and Thunderbird to capture detailed stack traces
• Configure SentinelOne agents to monitor browser process behavior for signs of exploitation
• Implement web proxy logging to identify potential exploit delivery attempts
• Set up alerts for high-frequency JIT compilation failures that may indicate exploitation attempts

How to Mitigate CVE-2025-14324

Immediate Actions Required

• Update Mozilla Firefox to version 146 or later immediately
• Update Mozilla Firefox ESR to version 115.31 or 140.6 or later
• Update Mozilla Thunderbird to version 146 or later
• Update Mozilla Thunderbird ESR to version 140.6 or later
• Prioritize patching systems that access untrusted web content or handle external emails

Patch Information

Mozilla has released security updates addressing this vulnerability across multiple product lines. Detailed patch information is available in the following security advisories:

• Mozilla Security Advisory MFSA-2025-92
• Mozilla Security Advisory MFSA-2025-93
• Mozilla Security Advisory MFSA-2025-94
• Mozilla Security Advisory MFSA-2025-95
• Mozilla Security Advisory MFSA-2025-96

Organizations should deploy these updates through their standard patch management processes, prioritizing internet-facing systems.

Workarounds

• Disable JIT compilation in Firefox by navigating to about:config and setting javascript.options.ion to false (note: this significantly impacts performance)
• Enable enhanced security settings in Thunderbird to prevent JavaScript execution in email content
• Implement network-level content filtering to block known malicious JavaScript patterns
• Consider using browser isolation technologies for high-risk users until patches can be deployed
• Restrict browsing to trusted sites only on systems where patching cannot be immediately performed

# Firefox JIT Disabling Configuration (Temporary Workaround)
# Navigate to about:config in Firefox and set:
# javascript.options.ion = false
# javascript.options.baselinejit = false
# javascript.options.native_regexp = false

# Note: Disabling JIT significantly degrades JavaScript performance
# This is a temporary workaround - apply the official patch as soon as possible