CVE-2026-109748 in Firefox
Summary
by MITRE • 10/13/2026
Use-after-free in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox 158.
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Analysis
by VulDB Data Team • 10/13/2026
The identified vulnerability represents a critical memory management error within Mozilla Firefox, specifically affecting the execution environment of WebAssembly components via its JavaScript interface. As a use-after-free flaw, this defect occurs when the application attempts to access memory that has already been deallocated or freed by the system's garbage collector or explicit cleanup routines. In the context of WebAssembly, which operates as a sandboxed binary format designed for high-performance execution in web browsers, such errors are particularly dangerous because they can bypass standard security boundaries if exploited correctly. The vulnerability resides deep within the engine responsible for interpreting and executing Wasm bytecode, where pointers to memory regions may remain valid in code logic even after the underlying data structures have been destroyed or reallocated for other purposes.
From a technical perspective, this flaw allows an attacker who controls the input to trigger a state where a dangling pointer is dereferenced. When the browser processes maliciously crafted WebAssembly modules embedded within a webpage, it may allocate memory buffers to handle runtime operations such as linear memory access or function calls. If these buffers are freed prematurely while references to them persist in active execution contexts, subsequent reads or writes will target invalid memory addresses. This can lead to arbitrary code execution if the attacker can control the data written into the reused memory space, effectively achieving a remote code execution scenario within the browser process sandbox. The complexity of WebAssembly's type system and just-in-time compilation mechanisms often makes it difficult for static analysis tools to detect these timing-dependent race conditions or logic errors without extensive dynamic testing.
The operational impact of this vulnerability is severe, as it compromises the integrity and confidentiality of user data processed by web applications utilizing advanced computational features. An attacker could craft a malicious website that loads a specially designed WebAssembly module, triggering the use-after-free condition upon interaction. Successful exploitation would allow the execution of arbitrary code with the privileges of the browser process, potentially leading to full system compromise depending on sandbox escape techniques employed alongside this initial foothold. This affects users across all platforms where Firefox is deployed, including Windows, macOS, and Linux distributions that utilize version 157 or earlier builds. The risk is amplified by the increasing adoption of WebAssembly for performance-critical web applications, making it a more attractive target for drive-by download attacks and supply chain compromises targeting popular libraries.
Mitigation strategies primarily involve immediate software updates to address the root cause within the engine's memory management logic. Users must upgrade Mozilla Firefox to version 158 or later, where the patch ensures that pointers are properly nullified after deallocation and that access checks are enforced before any memory operation occurs on WebAssembly components. For organizations managing large fleets of endpoints, automated deployment tools should be configured to prioritize this update due to its high severity rating. Additionally, developers integrating WebAssembly into their applications should adhere strictly to secure coding practices, validating all inputs passed to Wasm modules and avoiding the use of deprecated or unsafe APIs that might expose low-level memory operations. Security teams should also monitor for indicators of compromise related to unusual browser behavior or unexpected network connections originating from web processes, as these may signal active exploitation attempts in environments where patching is delayed.
This vulnerability aligns with Common Weakness Enumeration identifier CWE-416, which describes use-after-free conditions resulting from improper memory management. In the context of cyber attack frameworks such as MITRE ATT&CK, this flaw facilitates techniques associated with initial access and execution, specifically leveraging web-based technologies to bypass traditional perimeter defenses. The exploitation path typically involves social engineering or malicious ad networks delivering the crafted Wasm module, followed by local privilege escalation if sandbox escapes are combined with other vulnerabilities. Continuous monitoring of browser telemetry and enforcing strict content security policies can further reduce the attack surface by limiting which scripts and modules are permitted to execute within the browsing context.