CVE-2026-100765 in Firefox
Summary
by MITRE • 09/29/2026
Use-after-free in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox ESR 153.4 and Firefox 157.
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Analysis
by VulDB Data Team • 09/29/2026
The identified vulnerability represents a critical memory safety issue within the JavaScript engine's handling of WebAssembly components, specifically classified as an use-after-free condition. In modern web architectures, WebAssembly serves as a binary instruction format for near-native performance on the web, relying heavily on precise memory management to interact with host environments and JavaScript objects. When a program allocates memory for a specific object or data structure and subsequently frees that memory while retaining references to it, any subsequent attempt to access that freed memory constitutes an use-after-free error. In this context, the flaw likely stems from improper lifecycle management within the WebAssembly component interface, where pointers or handles to internal structures are not correctly invalidated after deallocation, allowing stale references to persist in the execution stack or global state.
From a technical perspective, this vulnerability exploits the gap between high-level JavaScript abstractions and low-level memory operations managed by the underlying engine such as SpiderMonkey. The attacker can potentially trigger the allocation of specific WebAssembly resources followed by their premature release through crafted script logic or malicious module instantiation sequences. Because the reference to the freed memory block remains valid in certain contexts, an adversary who controls the content loaded into that memory region before it is reallocated for a different purpose can manipulate the data read from those addresses. This scenario creates a classic race condition or state inconsistency where the application behaves unpredictably based on how the operating system's memory allocator repurposes the reclaimed space, often leading to arbitrary code execution if the attacker can control both the content written into the freed block and the subsequent access pattern.
The operational impact of this vulnerability is severe, as it allows for remote code execution without user interaction beyond visiting a maliciously crafted webpage or loading a compromised WebAssembly module. Attackers can leverage this flaw to bypass browser sandboxing mechanisms, escalate privileges within the browser process, and potentially compromise the underlying host system by executing arbitrary shellcode or installing persistent malware. The presence of such vulnerabilities in widely deployed browsers like Firefox poses significant risks to enterprise environments relying on web-based applications that utilize WebAssembly for performance-critical tasks. It undermines the integrity guarantees provided by modern security features including Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR), as successful exploitation often requires precise memory layout control which can sometimes be achieved through heap spraying techniques or side-channel attacks against allocator behavior.
This flaw aligns with Common Weakness Enumeration identifier CWE-416, which defines use-after-free errors resulting from improper invalidation of references after deallocation. Furthermore, in the context of the MITRE ATT&CK framework for enterprise security, this vulnerability facilitates initial access and execution techniques commonly associated with drive-by compromise scenarios where attackers deploy weaponized WebAssembly modules to exploit browser engine flaws. The exploitation path typically involves crafting a malicious HTML page that triggers the specific sequence leading to the memory corruption, making it a high-value target for threat actors seeking zero-day exploits against popular web browsers.
Mitigation strategies primarily involve applying the vendor-provided patches released in Firefox ESR 153.4 and Firefox 157, which address the underlying logic errors in the WebAssembly component handling routines. Organizations should ensure that all client endpoints are updated to these versions or later releases containing similar fixes for related memory safety issues. Additionally, implementing strict Content Security Policy directives can help restrict the loading of untrusted scripts and modules, reducing the attack surface available to potential exploiters. Developers utilizing WebAssembly in their applications should also adopt secure coding practices such as rigorous input validation and avoiding dynamic code generation where possible, while relying on static analysis tools that detect memory management anomalies during the software development lifecycle to prevent similar defects from reaching production environments.