CVE-2025-13024: Mozilla Firefox JIT RCE Vulnerability

CVE-2025-13024 Overview

CVE-2025-13024 is a JIT (Just-In-Time) miscompilation vulnerability in the JavaScript Engine's JIT component affecting Mozilla Firefox and Thunderbird. This vulnerability allows attackers to potentially execute arbitrary code through maliciously crafted JavaScript that exploits flaws in the JIT compilation process. The vulnerability affects Firefox versions prior to 145 and Thunderbird versions prior to 145.

Critical Impact

This JIT miscompilation vulnerability could allow remote attackers to achieve code execution by crafting malicious JavaScript that triggers incorrect code generation during JIT compilation, potentially compromising user systems through malicious web pages.

Affected Products

• Mozilla Firefox < 145
• Mozilla Thunderbird < 145

Discovery Timeline

• 2025-11-11 - CVE-2025-13024 published to NVD
• 2025-11-19 - Last updated in NVD database

Technical Details for CVE-2025-13024

Vulnerability Analysis

This vulnerability stems from a JIT miscompilation issue within Firefox's JavaScript engine. JIT compilers translate JavaScript code into optimized machine code at runtime to improve performance. When the JIT compiler incorrectly optimizes or generates machine code, it can introduce security vulnerabilities that bypass normal JavaScript security constraints.

JIT miscompilation vulnerabilities are particularly dangerous because they can lead to type confusion, incorrect bounds checking elimination, or other memory safety violations. These flaws allow attackers to craft JavaScript that appears benign but, when JIT-compiled, produces machine code with exploitable behavior.

The vulnerability is classified under CWE-733 (Compiler Optimization Removal or Modification of Security-critical Code), indicating that security-critical operations may be incorrectly optimized away or modified during the JIT compilation process.

Root Cause

The root cause is a flaw in the JIT compiler's optimization pipeline within Mozilla's SpiderMonkey JavaScript engine. During the compilation phase, the JIT compiler makes assumptions about code behavior that may not hold true in all cases. When these assumptions are violated through carefully crafted JavaScript, the resulting machine code can exhibit undefined behavior, potentially allowing memory corruption or type confusion attacks.

Attack Vector

The attack vector is network-based, requiring no user interaction beyond visiting a malicious webpage. An attacker can host JavaScript code on a website or inject it through advertising networks, cross-site scripting, or compromised third-party scripts. When a vulnerable Firefox or Thunderbird client executes the malicious JavaScript, the JIT compiler generates flawed machine code that can be exploited.

The attacker does not require any privileges to exploit this vulnerability. The attack can be delivered through:

• Malicious websites directly visited by the user
• Compromised legitimate websites
• Malicious advertisements served through ad networks
• Embedded content in emails viewed with Thunderbird

The vulnerability mechanism involves crafting JavaScript that triggers specific optimization paths in the JIT compiler. When these optimizations are applied incorrectly, the resulting machine code may contain memory safety violations. For detailed technical information, refer to Mozilla Bug Report #1992902 and the Mozilla Security Advisory MFSA-2025-87.

Detection Methods for CVE-2025-13024

Indicators of Compromise

• Unusual JavaScript execution patterns in browser process memory that exhibit type confusion characteristics
• Crash reports related to SpiderMonkey JIT compilation errors or memory access violations
• Anomalous network connections originating from browser processes following JavaScript execution
• Unexpected child processes spawned by Firefox or Thunderbird processes

Detection Strategies

• Monitor browser crash reports for JIT-related exceptions and memory corruption indicators
• Implement network-level detection for known malicious JavaScript patterns targeting JIT vulnerabilities
• Deploy endpoint detection solutions capable of monitoring browser process behavior for exploitation attempts
• Analyze JavaScript content in web traffic for obfuscated code patterns commonly used in JIT exploitation

Monitoring Recommendations

• Enable enhanced crash reporting in Firefox to capture detailed JIT compilation failures
• Monitor browser process memory usage for abnormal patterns that may indicate heap spray or memory corruption attempts
• Implement Content Security Policy (CSP) headers on internal web applications to restrict JavaScript execution sources
• Utilize browser telemetry and enterprise logging to track unusual JavaScript execution across managed endpoints

How to Mitigate CVE-2025-13024

Immediate Actions Required

• Update Mozilla Firefox to version 145 or later immediately
• Update Mozilla Thunderbird to version 145 or later immediately
• Enable automatic updates to ensure timely deployment of future security patches
• Consider temporarily disabling JIT compilation as a workaround until patches can be applied (note: this may impact performance)

Patch Information

Mozilla has released Firefox 145 and Thunderbird 145 to address this vulnerability. Organizations should prioritize deployment of these updates across all managed systems. Security advisories are available at:

• Mozilla Security Advisory MFSA-2025-87
• Mozilla Security Advisory MFSA-2025-90

Enterprise environments using Firefox ESR should consult Mozilla's security advisories for ESR-specific guidance.

Workarounds

• Disable JIT compilation by setting javascript.options.ion to false in about:config (impacts browser performance)
• Use browser isolation or sandboxing solutions to contain potential exploitation attempts
• Implement network-level filtering to block access to known malicious domains
• Consider using alternative browsers temporarily for high-risk activities until patching is complete

# Firefox Configuration Workaround (via user.js or policies)
# Add to user.js in Firefox profile directory to disable JIT:
user_pref("javascript.options.ion", false);
user_pref("javascript.options.baselinejit", false);
user_pref("javascript.options.native_regexp", false);