CVE-2026-100788 in Firefox
Summary
by MITRE • 09/29/2026
Invalid pointer 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 resides within the JavaScript engine's handling of WebAssembly components, specifically involving an invalid pointer dereference that can lead to memory corruption or unexpected application behavior. This flaw typically arises when the Just-In-Time compiler or the runtime environment fails to properly validate memory boundaries before accessing data structures associated with a WebAssembly module. In complex web applications that leverage heavy computational tasks via WebAssembly, such as image processing, video encoding, or scientific simulations, the engine must maintain strict isolation between JavaScript heap memory and linear WebAssembly memory. When this boundary checking is compromised due to an invalid pointer reference, it indicates a failure in the type safety mechanisms designed to prevent out-of-bounds access. Such errors are particularly dangerous because they can allow malicious actors to read sensitive data from adjacent memory regions or write arbitrary values into unintended locations, potentially leading to information disclosure or code execution depending on the specific context and exploitability of the corrupted state.
From a technical perspective, this issue aligns with common categories of memory safety violations found in high-performance web technologies. It is closely related to CWE-125, which describes Out-of-bounds Read vulnerabilities, as well as CWE-787, which covers Out-of-bounds Write scenarios if the invalid pointer leads to a write operation beyond allocated limits. The vulnerability likely stems from edge cases in how Firefox's SpiderMonkey engine manages garbage collection cycles or memory reallocation for WebAssembly instances. If an attacker can trigger specific sequences of JavaScript calls that manipulate WebAssembly exports or imports, they might force the runtime into a state where it attempts to access freed or unmapped memory pages. This type of flaw is often difficult to detect through standard static analysis because it requires precise timing and specific heap states to manifest, making dynamic fuzzing and rigorous testing essential for discovery.
The operational impact of this vulnerability extends beyond simple application crashes, although denial-of-service remains a primary immediate consequence. If the invalid pointer dereference results in an out-of-bounds read, attackers could potentially exfiltrate sensitive information such as session tokens, cryptographic keys, or user data stored in adjacent memory buffers. In more severe cases where the corruption affects control flow structures like function pointers or return addresses on the stack, it may lead to remote code execution with the privileges of the browser process. This poses a significant risk to users who visit maliciously crafted web pages designed to exploit this weakness through specially constructed WebAssembly binaries and JavaScript payloads. The trust model of the web relies heavily on the assumption that sandboxed environments like browsers will not allow such escapes, making these vulnerabilities critical security concerns for both end-users and enterprise deployments relying on Firefox ESR versions for stability and security compliance.
Mitigation strategies primarily involve applying the vendor-provided patches released in Firefox ESR 153.4, Firefox 157, and Firefox ESR 140.17, which contain fixes to the underlying memory management logic within the WebAssembly component handler. Organizations should prioritize updating their browser infrastructure immediately to close this attack vector. For developers utilizing WebAssembly in production environments, it is advisable to implement strict Content Security Policy directives that restrict the loading of external scripts and modules where possible, reducing the surface area for potential exploitation. Additionally, enabling advanced security features such as ASLR and DEP can provide additional layers of defense against memory corruption exploits even if a vulnerability were present. Continuous monitoring of browser update channels and automated patch management systems are recommended to ensure timely remediation of similar vulnerabilities in future releases, maintaining alignment with industry best practices for web application security and endpoint protection standards outlined by frameworks like MITRE ATT&CK under the technique categories related to execution and privilege escalation via memory corruption.