CVE-2026-100793 in Firefox
Summary
by MITRE • 09/29/2026
JIT miscompilation in the JavaScript Engine component. This vulnerability was fixed in Firefox 157.
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Analysis
by VulDB Data Team • 09/29/2026
The identified vulnerability represents a critical failure within the Just-In-Time compilation subsystem of the browser's JavaScript engine, specifically affecting versions prior to Firefox 157. The core technical flaw stems from an incorrect code generation process where the compiler fails to accurately translate high-level JavaScript operations into optimized machine code instructions. This miscompilation typically arises when the optimizer makes aggressive assumptions about variable types or memory states that do not hold true during runtime execution, leading to a divergence between the expected logical flow and the actual executed binary instructions. Such errors are particularly dangerous because they bypass standard security checks implemented at the interpreter level, allowing malicious scripts to exploit inconsistencies in how data is handled within the optimized code paths.
From an operational perspective, this vulnerability enables remote attackers to achieve arbitrary code execution on a victim's system through a crafted web page or script. By carefully constructing JavaScript payloads that trigger the specific conditions causing the JIT miscompilation, an attacker can manipulate memory layout and control flow in ways that were not intended by the language specification. This capability effectively neutralizes several built-in browser security mitigations, such as sandboxing boundaries and type safety checks, which rely on correct execution of underlying engine logic. Consequently, a successful exploit could lead to full system compromise, allowing the attacker to install malware, exfiltrate sensitive data, or establish persistent access without user interaction beyond visiting the malicious site.
The classification of this issue aligns with Common Weakness Enumeration standards for improper code generation and memory corruption vulnerabilities. It is closely related to CWE-754, which addresses incorrect check of unusual condition, as well as CWE-120, involving buffer overflows resulting from flawed compilation logic that fails to enforce proper bounds checking or type integrity. In the context of cyber offense modeling, this vulnerability maps directly to MITRE ATT&CK techniques associated with client-side exploitation and JIT spraying, where attackers leverage engine bugs to bypass modern browser defenses like Control Flow Integrity and Data Execution Prevention. The severity is heightened by the fact that JavaScript engines are ubiquitous in web browsing environments, making any such flaw a high-value target for threat actors seeking widespread impact.
Mitigation strategies primarily involve ensuring all clients update their browsers to version 157 or later, where the specific logic errors within the JIT compiler have been corrected and validated through extensive fuzzing and regression testing. For organizations managing large fleets of endpoints, automated patch management systems should be configured to prioritize this security update due to its high severity rating. Additionally, implementing strict Content Security Policy headers can help mitigate potential exploitation by restricting the sources from which scripts are loaded, thereby reducing the attack surface available to adversaries attempting to deliver malicious payloads that trigger the JIT flaw. Continuous monitoring for anomalous browser behavior and keeping exploit mitigation technologies such as ASLR enabled further reduces the likelihood of successful compromise even if a variant of this vulnerability were present in unpatched systems.