CVE-2026-100792 in Firefox
Summary
by MITRE • 09/29/2026
JIT miscompilation in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, and Firefox ESR 140.17.
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Analysis
by VulDB Data Team • 09/29/2026
The identified vulnerability represents a critical failure within the Just-In-Time compilation subsystem of Mozilla's JavaScript engine when processing WebAssembly components. This miscompilation indicates that the compiler generated incorrect machine code for valid Wasm instructions, leading to undefined behavior during execution. Such errors typically arise from complex interactions between the optimizer and the backend code generator, where assumptions about register allocation, memory layout, or control flow are incorrectly applied. The flaw allows a maliciously crafted WebAssembly module to exploit these discrepancies, potentially causing the browser process to execute arbitrary logic that deviates significantly from the intended specification of the Wasm bytecode. This type of issue is particularly dangerous because it bypasses many traditional security checks that rely on predictable execution paths, as the CPU executes instructions that were never semantically equivalent to the source code provided by the developer or attacker.
From a technical perspective, this flaw aligns with CWE-471, which describes modification of assumed immutable data, and more broadly with memory safety violations often categorized under CWE-120 Buffer Overflow if it leads to out-of-bounds access due to incorrect pointer arithmetic generated by the JIT compiler. In the context of modern browser architecture, such vulnerabilities are frequently mapped to MITRE ATT&CK techniques related to Execution through Interpreted Languages or potentially Code Injection via WebAssembly modules. The impact is severe because a successful exploit could lead to arbitrary code execution within the sandboxed environment of the browser process. While browsers employ multiple layers of defense including sandboxing and memory protection, a JIT miscompilation can often circumvent these by manipulating internal state in ways that bypass bounds checks or heap metadata validation, effectively granting an attacker control over the program counter or data pointers.
The operational impact of this vulnerability extends beyond simple crashes to potential remote code execution scenarios if combined with other primitives such as type confusion or use-after-free conditions. Attackers could leverage this miscompilation to escape the WebAssembly sandbox and interact directly with host functions, potentially accessing sensitive user data stored in memory or executing commands on the underlying operating system. The risk is amplified by the increasing prevalence of WebAssembly in web applications for performance-critical tasks like video processing, gaming, and cryptographic operations. Users visiting compromised websites that serve malicious Wasm modules are at immediate risk until they update their browser software. This vulnerability underscores the complexity of maintaining correctness in highly optimized compilers where edge cases in instruction scheduling or register spilling can lead to catastrophic security failures.
Mitigation for this issue relies entirely on updating to patched versions of Firefox, specifically ESR 153.4, version 157, and ESR 140.17 as indicated by the vendor. These releases contain fixes that likely involve rigorous testing of JIT-generated code against known Wasm specifications, improved validation logic within the compiler pipeline, or potentially disabling specific optimization passes that were prone to error until they can be proven safe. For organizations managing large fleets of endpoints, it is imperative to prioritize patching these browser versions immediately to close this attack vector. Additionally, developers should ensure their WebAssembly modules are compiled with strict safety checks enabled and avoid using experimental features in production environments where JIT bugs may not yet have been fully vetted by the community and vendor security teams. Continuous monitoring for unusual network activity or process behavior can also help detect exploitation attempts that might bypass static defenses.