CVE-2026-92040 in Firefox
Summary
by MITRE • 09/15/2026
Use-after-free in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox 156.
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Analysis
by VulDB Data Team • 09/15/2026
The identified vulnerability represents a critical memory safety issue within the JavaScript engine's handling of WebAssembly components, specifically manifesting as an use-after-free condition. In modern web browsers, the execution environment for WebAssembly relies heavily on complex garbage collection mechanisms and memory management subsystems to handle dynamic allocations and deallocations efficiently. When a program allocates memory for a WebAssembly component or its associated data structures, it expects that reference to remain valid until explicitly freed by the runtime. However, in this specific instance, the browser's internal logic failed to properly synchronize these operations, leading to a scenario where a pointer continues to be used after the underlying memory block has been returned to the system allocator and potentially reallocated for other purposes. This type of flaw is fundamentally rooted in improper management of object lifecycles within the JIT (Just-In-Time) compilation layer or the WebAssembly runtime interface, creating a discrepancy between logical state and physical memory layout.
From a technical perspective, this vulnerability aligns closely with CWE-416, which defines use-after-free errors as conditions where software uses memory after it has been freed. The operational impact of such a flaw is severe because an attacker can potentially craft malicious WebAssembly code or manipulate JavaScript interactions to trigger the deallocation sequence while maintaining active references to that memory region. By carefully controlling the timing and content of subsequent allocations, an adversary may overwrite the freed memory with controlled data structures. When the browser subsequently attempts to access the stale pointer, it effectively reads from or writes to attacker-controlled memory locations. This capability allows for arbitrary code execution within the context of the web page's sandbox, potentially leading to full system compromise if additional exploitation techniques are combined to escape the browser container.
The presence of this vulnerability highlights ongoing challenges in maintaining strict memory safety guarantees in high-performance scripting engines that bridge native C++ codebases with managed JavaScript environments. WebAssembly components often involve complex interactions between the host environment and the guest module, requiring precise tracking of reference counts and pointer validity across different execution threads or asynchronous callbacks. The failure to enforce these constraints consistently results in exploitable race conditions or logic errors where memory is prematurely reclaimed. Security researchers have long noted that use-after-free vulnerabilities remain among the most prevalent and dangerous classes of bugs in browser engines due to their direct impact on exploitability and stability, often serving as primary vectors for drive-by download attacks and zero-day exploits targeting end-users who visit compromised websites hosting malicious WebAssembly payloads.
Mitigation strategies primarily rely on the timely application of vendor-provided patches, such as the fix included in Firefox version 156. Users are strongly advised to update their browsers immediately to ensure that the underlying memory management routines correctly validate pointer validity before dereferencing them and prevent premature deallocation during active use phases. Beyond patching, defense-in-depth measures include enabling browser security features like ASLR (Address Space Layout Randomization) and DEP/NX (Data Execution Prevention), which make exploitation of such vulnerabilities more difficult by randomizing memory layouts and preventing code execution in data-only regions. Additionally, developers integrating WebAssembly into their applications should adhere to strict input validation practices and avoid executing untrusted Wasm modules without proper sandboxing or isolation mechanisms provided by the browser's security model. Continuous monitoring for anomalous behavior and keeping all software dependencies up to date remain essential components of a robust cybersecurity posture against memory corruption vulnerabilities.