CVE-2026-2804 is a use-after-free vulnerability identified in the WebAssembly component of Mozilla Firefox browsers prior to version 148. Use-after-free vulnerabilities occur when a program continues to use memory after it has been freed, leading to undefined behavior that attackers can exploit to execute arbitrary code or cause denial of service. In this case, the flaw resides in the JavaScript engine's handling of WebAssembly, a low-level binary instruction format designed to run code at near-native speed within browsers. An attacker can craft malicious WebAssembly code embedded in a web page that, when processed by a vulnerable Firefox browser, triggers the use-after-free condition. This can allow remote attackers to execute arbitrary code in the context of the browser process, potentially leading to full system compromise or data theft. Although no public exploits are currently known, the vulnerability's presence in a widely used browser component makes it a critical concern. The vulnerability affects all Firefox versions before 148, though specific affected subversions are unspecified. No official CVSS score has been assigned yet, and no patches or mitigations have been linked at the time of publication. The vulnerability was reserved and published in February 2026, indicating recent discovery and disclosure.

If exploited, CVE-2026-2804 could allow attackers to execute arbitrary code remotely by convincing users to visit malicious or compromised websites containing crafted WebAssembly code. This can lead to complete compromise of the browser process, enabling theft of sensitive information such as cookies, credentials, or session tokens, and potentially allowing attackers to pivot to the underlying operating system. The use-after-free nature of the bug also means it can cause browser crashes, leading to denial of service. Organizations relying on Firefox for secure web access, especially those handling sensitive data or operating in high-risk environments, face significant confidentiality and integrity risks. The vulnerability's exploitation does not require authentication but does require user interaction (visiting a malicious site). Given Firefox's global market share, the scope of affected systems is broad, impacting individual users, enterprises, and government agencies worldwide. The absence of known exploits currently reduces immediate risk but also underscores the urgency for patching once fixes are available.

To mitigate CVE-2026-2804, organizations and users should promptly update Firefox to version 148 or later once the patch is released by Mozilla. Until then, consider disabling WebAssembly execution in Firefox settings or via enterprise policies to reduce attack surface, though this may impact performance and functionality of legitimate web applications relying on WebAssembly. Employ browser security features such as enhanced sandboxing, strict content security policies (CSP), and script blocking extensions to limit exposure to malicious scripts. Network-level protections like web filtering and intrusion prevention systems can help block access to known malicious domains hosting exploit code. Regularly monitor Mozilla security advisories for updates and patches. For high-security environments, consider using alternative browsers with no known WebAssembly vulnerabilities or running Firefox in isolated environments to contain potential exploits. Educate users about the risks of visiting untrusted websites and the importance of timely browser updates.