CVE-2026-117898 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the JavaScript Engine: JIT component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/28/2026
The identified vulnerability represents a critical memory safety issue within the Just-In-Time compilation subsystem of the Mozilla SpiderMonkey JavaScript engine, specifically classified as an use-after-free condition. In software architecture, particularly within high-performance interpreters like those used in modern web browsers, JIT compilers optimize code execution by translating dynamic bytecode into native machine instructions at runtime to accelerate performance. This process involves complex memory management where objects are allocated on heaps and stacks for temporary storage during compilation or optimization phases. A use-after-free vulnerability occurs when the program continues to use a pointer after that memory has been freed, typically because the reference tracking mechanism failed to invalidate pointers associated with deallocated resources. In this specific context, the flaw likely stems from an inconsistency in how the JIT compiler tracks object lifecycles during aggressive optimizations such as type inference or loop unrolling. When the garbage collector reclaims memory for a JavaScript object that is still referenced by a compiled native code path, subsequent execution of that optimized code attempts to access invalid memory addresses. This scenario creates a window where an attacker can manipulate the state of freed memory to control program flow or read sensitive data from adjacent heap regions.
From a technical perspective, this flaw falls under CWE-416, which defines use-after-free errors as a subset of improper resource management vulnerabilities. The severity is amplified by its location within the JIT engine rather than the core interpreter logic. Because JIT code runs at native speed and often bypasses some of the safety checks present in interpreted execution paths, exploiting this vulnerability can lead to arbitrary code execution with high reliability. Attackers typically leverage such flaws through crafted JavaScript payloads embedded in malicious web pages or extensions. By triggering specific sequences that cause premature deallocation while maintaining active references within JIT-compiled functions, an adversary can achieve heap spraying techniques to gain control over the instruction pointer. This capability allows for full system compromise if the browser process is not sufficiently sandboxed, potentially leading to remote code execution on the victim's machine without any user interaction beyond visiting a malicious site or opening a compromised document that executes JavaScript content.
The operational impact of this vulnerability extends beyond immediate exploitation risks to include broader stability and security posture concerns for organizations relying on Firefox-based infrastructure. Unpatched instances are susceptible to denial-of-service conditions if the memory corruption causes crashes, but more critically, they expose users to sophisticated phishing campaigns or drive-by download attacks that utilize advanced persistent threat techniques. The ATT&CK framework categorizes such exploits under T1203, which covers exploitation for client execution, and potentially T1059, command and scripting interpreter abuse if the vulnerability allows for further payload delivery within the browser context. Given that Firefox is widely used in enterprise environments often integrated with single sign-on solutions or internal web applications, a successful exploit could serve as an initial access vector into corporate networks. The lack of mitigation mechanisms like Control Flow Integrity (CFI) in older JIT implementations makes these vulnerabilities particularly dangerous compared to modern browsers that employ stricter memory isolation and sandboxing protocols.
Mitigation strategies must prioritize immediate patch deployment across all client endpoints and server-side proxies that render web content using the affected engine versions. Organizations should enforce strict update policies ensuring that Firefox 159 or later, as well as Firefox ESR 153.6 or later, are installed universally. Beyond version upgrades, implementing browser hardening techniques such as disabling unnecessary JavaScript features in untrusted contexts can reduce the attack surface. Security teams should also monitor for indicators of compromise related to JIT compiler anomalies, such as unusual memory spikes or crashes associated with specific web applications. Additionally, deploying Content Security Policy headers and enabling sandbox attributes on iframes can limit the potential blast radius of any successful exploitation attempt by restricting access to sensitive APIs or external resources. Regular vulnerability scanning focused on browser versions and component updates remains essential for maintaining a resilient security posture against evolving memory corruption threats in web technologies.