CVE-2026-100817 in Firefox
Summary
by MITRE • 09/29/2026
Other issue in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox 157.
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Analysis
by VulDB Data Team • 09/29/2026
The identified security flaw resides within the JavaScript engine's handling of WebAssembly components, specifically affecting Mozilla Firefox prior to version 157. This vulnerability represents a critical failure in the boundary checks or memory management logic that governs how JavaScript code interacts with compiled WebAssembly modules. In modern web architectures, WebAssembly serves as a binary instruction format for executable programs, allowing high-performance applications like games and video editors to run efficiently within browser sandboxes. However, when the bridge between the dynamic nature of JavaScript and the static compilation model of WebAssembly is compromised, it can lead to severe memory corruption issues. The specific defect likely involves improper validation of data types or buffer boundaries during the execution of WebAssembly instructions invoked from JavaScript contexts.
From a technical perspective, this type of vulnerability typically falls under categories such as out-of-bounds write or use-after-free conditions, which are classified under CWE-120 and CWE-416 respectively in the Common Weakness Enumeration framework. These flaws occur when the browser fails to correctly enforce memory safety constraints, allowing maliciously crafted WebAssembly modules to read from or write to arbitrary memory locations outside their allocated bounds. Such behavior can lead to data corruption, application crashes, or potentially remote code execution if an attacker can control the contents of the overwritten memory regions. The complexity arises because WebAssembly operates with its own linear memory space, and errors in how JavaScript accesses this space via imported functions or global variables can bypass standard security checks designed for pure JavaScript environments.
The operational impact of this vulnerability is significant due to the widespread adoption of WebAssembly across critical web applications. An attacker could potentially exploit this flaw by hosting a malicious webpage containing a specially crafted WebAssembly component that triggers the memory corruption when executed in an affected version of Firefox. Successful exploitation might allow the attacker to bypass browser security mechanisms such as Same-Origin Policy or sandbox restrictions, leading to unauthorized access to sensitive user data stored locally on the victim's machine. Furthermore, depending on the specific nature of the memory error, it could facilitate privilege escalation within the context of the web process, potentially impacting other tabs or extensions running in the same browser instance if isolation boundaries are not strictly enforced by the underlying engine architecture.
Mitigation for this issue was addressed through a comprehensive patch included in Firefox version 157 and subsequent releases. Users should immediately update their browsers to ensure they benefit from these security fixes which likely involve stricter type checking, enhanced bounds verification during WebAssembly instantiation or execution, and improved isolation between JavaScript heap memory and Wasm linear memory. Additionally, developers integrating WebAssembly into their applications are advised to adhere strictly to secure coding practices, ensuring that all inputs passed to WebAssembly modules are validated before processing. Security teams should monitor for any indicators of compromise related to unusual network activity from web processes or unexpected crashes in browsers running complex WebAssembly workloads until the update is fully deployed across all client systems.