Description

Invalid pointer in the JavaScript Engine: JIT component. This vulnerability was fixed in Firefox 157.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.8",
  "pubDate": "2026-09-29T13:17:46.440Z",
  "pubdate": "2026-09-29T13:17:46.440Z",
  "executiveSummary": "This vulnerability involves an invalid pointer management issue within the JIT (Just-In-Time) compilation component of the Firefox JavaScript engine.\nThe flaw allows a remote attacker to trigger a memory corruption state, which can potentially lead to arbitrary code execution or a crash of the rendering process.\nThe issue affects Firefox versions prior to 157.\nThe primary risk lies in the manipulation of machine code generation, where improper pointer validation or tracking during optimization passes results in a use-after-free or out-of-bounds access condition.\nSuccessful exploitation requires the victim to visit a specially crafted malicious web page containing JavaScript designed to trigger the JIT optimization edge cases.\nOnce the invalid pointer is dereferenced, the attacker may gain the ability to execute arbitrary code within the context of the content process, bypassing sandbox protections if chained with additional exploits.\nThis vulnerability underscores the risks inherent in complex JIT compilation engines, where the rapid optimization of bytecode into native machine instructions can create transient memory safety violations.",
  "technicalDetails": "The vulnerability originates in the JIT component of the Firefox JavaScript engine, where the compilation pipeline fails to maintain pointer integrity during the optimization phase of bytecode execution. Specifically, the engine's speculative optimization logic—which makes assumptions about type consistency and object memory layout—occasionally produces invalidated pointers if the underlying heap state changes during the optimization transition.\nThe root cause is a failure in the JIT's alias analysis or internal representation tracking, where a pointer managed by the engine is incorrectly cached or reused after the corresponding memory block has been deallocated or reallocated. When the JIT compiler generates machine code for a specific JavaScript hot path, it assumes the address of an object or a buffer remains valid throughout the execution of the optimized instruction block.\nThe exploitation flow typically begins by identifying a JavaScript pattern that forces the JIT compiler to trigger a specific optimization, such as an ArrayBuffer re-allocation or an object shape change. By inducing a Garbage Collection (GC) cycle or an object transition precisely while the JIT engine is performing its optimization pass, the attacker can cause the JIT-generated machine code to reference a stale memory location.\nOnce the invalid pointer is captured, the attacker can employ heap grooming techniques—such as spraying the heap with controlled JavaScript objects—to ensure that the dereferenced pointer maps to an attacker-controlled structure. This allows the attacker to achieve a read/write primitive within the memory space of the affected process.\nIn the context of modern browser security, this primitive is often used to overwrite function pointers or data structures within the JavaScript engine's internal environment (such as the object's vtable or the JSObject metadata). By redirecting execution flow, the attacker can bypass security mitigations like Control Flow Guard (CFG) or execute ROP (Return Oriented Programming) chains if the memory region is executable.\nThe vulnerability is limited to the content process, which is responsible for rendering web content. As a result, the attacker must generally chain this flaw with a sandbox escape or an escalation of privilege exploit to achieve full system compromise. The absence of strict memory tagging or hardware-level pointer authentication within this specific JIT instruction sequence facilitates the exploitation of these transient memory corruption states."
}