CVE-2026-118026 in Firefox
Summary
by MITRE • 10/27/2026
Invalid pointer in the JavaScript: GC component. This vulnerability was fixed in Firefox 159.
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Analysis
by VulDB Data Team • 10/27/2026
The identified vulnerability resides within the garbage collection subsystem of Mozilla's SpiderMonkey JavaScript engine, specifically involving an invalid memory pointer dereference that can lead to a use-after-free condition or similar memory corruption error. In complex web applications and modern browser environments, the JavaScript runtime is responsible for managing dynamic memory allocation and deallocation through automated garbage collection mechanisms designed to reclaim unused objects from heap memory. When this process encounters malformed state transitions or race conditions during object finalization, it may retain references to memory regions that have already been freed or reallocated by other parts of the system. This invalid pointer situation allows an attacker who can trigger specific JavaScript execution paths within a compromised webpage to manipulate how the browser handles these dangling references, potentially leading to arbitrary code execution with the privileges of the victim user if exploited successfully in conjunction with additional exploitation techniques such as heap spraying or type confusion attacks.
From a technical perspective, this flaw highlights critical challenges in maintaining memory safety within high-performance scripting engines that operate without built-in bounds checking or automatic reference counting guarantees found in safer languages like Rust or Go. The garbage collector must accurately track object lifecycles and ensure that no active references exist before reclaiming memory; failure to do so results in the program attempting to access deallocated memory, which violates fundamental principles of secure software design often categorized under CWE-416 Use After Free or CWE-825 Expired Pointer Dereference. Such vulnerabilities are particularly dangerous because they can bypass many traditional security mitigations including stack canaries and non-executable stacks if the attacker gains sufficient control over register values or memory layout through precise manipulation of JavaScript object structures during the garbage collection phase.
The operational impact of this vulnerability is severe, as it potentially allows remote attackers to execute arbitrary code on a victim's machine simply by convincing them to visit a maliciously crafted website containing specially designed JavaScript payloads. This aligns with common attack vectors documented in MITRE ATT&CK framework under techniques such as T1059 Command and Scripting Interpreter or more specifically browser-based exploitation paths that leverage memory corruption for privilege escalation within the sandboxed environment of the web renderer process. Successful exploitation could lead to full system compromise, data exfiltration, installation of persistent malware, or further lateral movement depending on the surrounding security posture and available exploit chains against other components in the Firefox architecture including the content processes and their isolation boundaries.
Mitigation strategies primarily involve applying the vendor-provided patch included in Mozilla Firefox version 159 which addresses the underlying logic errors within the garbage collection routines responsible for tracking object references and managing heap memory states correctly during runtime execution cycles. Organizations should ensure that all endpoints running affected versions of Firefox are updated promptly to eliminate exposure to this class of memory corruption vulnerabilities while also enforcing strict content security policies and sandboxing configurations where possible to limit the blast radius in case future zero-day exploits emerge. Additionally, developers building web applications or extensions interacting with browser APIs should remain vigilant about input validation and avoid relying on undefined behaviors within JavaScript engines since even minor inconsistencies can be leveraged by sophisticated threat actors aiming to bypass modern defense-in-depth mechanisms deployed across enterprise environments.