CVE-2026-16363 in Firefox
Summary
by MITRE • 07/21/2026
JIT miscompilation in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox 153 and Firefox ESR 140.13.
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Analysis
by VulDB Data Team • 07/21/2026
This vulnerability represents a critical just-in-time compilation flaw within the JavaScript engine's interaction with WebAssembly components, specifically affecting the Firefox browser ecosystem. The issue manifests as a miscompilation error that occurs during the dynamic optimization phase of code execution, where the JIT compiler generates incorrect machine code from high-level JavaScript or WebAssembly instructions. Such miscompilations can lead to unpredictable program behavior and potentially exploitable conditions that compromise system security.
The technical flaw stems from insufficient validation mechanisms within the JIT compilation pipeline that processes WebAssembly modules executed through Firefox's JavaScript engine. When the compiler attempts to optimize WebAssembly code for performance, it may produce incorrect machine instructions due to improper handling of certain edge cases or optimization assumptions. This miscompilation can result in memory corruption, control flow hijacking, or other undefined behaviors that adversaries could potentially leverage for exploitation.
The operational impact of this vulnerability extends beyond simple performance degradation, as it creates potential attack vectors for remote code execution and privilege escalation scenarios. Attackers could craft malicious WebAssembly modules designed to trigger the specific JIT miscompilation path, leading to arbitrary code execution within the browser context. The vulnerability affects both regular Firefox releases and the extended support release channel, indicating a widespread impact across different deployment scenarios.
Organizations should immediately deploy the patched versions of Firefox including version 153 for regular releases and 140.13 for ESR deployments to mitigate this risk. Security teams should also implement monitoring for suspicious WebAssembly module execution patterns and consider network-level controls to restrict potentially malicious content. This vulnerability aligns with CWE-697, which addresses incorrect comparison issues in software systems, and may map to ATT&CK techniques related to code injection and privilege escalation through browser-based exploits.
The fix implemented by Mozilla addresses the underlying JIT compilation logic that was failing to properly validate WebAssembly instruction sequences during optimization phases. This correction ensures that the compiler maintains proper state management and validation checks throughout the entire compilation pipeline, preventing the generation of malformed machine code that could be exploited. Organizations should conduct thorough testing of their WebAssembly-dependent applications to ensure compatibility with the patched browser versions while maintaining security posture against this specific class of JIT-related vulnerabilities.