CVE-2026-2767 is a use-after-free vulnerability identified in the WebAssembly component of Mozilla Firefox and Thunderbird. Use-after-free (CWE-416) occurs when a program continues to use memory after it has been freed, leading to undefined behavior including potential arbitrary code execution. This vulnerability affects Firefox versions earlier than 148 and Firefox ESR versions earlier than 140.8, as well as Thunderbird versions earlier than 148 and ESR versions earlier than 140.8. The flaw resides in the JavaScript engine's handling of WebAssembly, a low-level bytecode format designed for high-performance web applications. An attacker can craft malicious WebAssembly code that triggers the use-after-free condition, allowing execution of arbitrary code in the context of the user running the browser or email client. The CVSS v3.1 base score of 8.8 reflects the vulnerability's high impact on confidentiality, integrity, and availability, with an attack vector of network (remote), low attack complexity, no privileges required, but requiring user interaction (e.g., visiting a malicious website or opening a malicious email). Although no exploits are currently known in the wild, the vulnerability poses a significant risk due to the widespread use of Firefox and Thunderbird. The vulnerability was reserved on February 19, 2026, and published on February 24, 2026. No patch links are provided yet, indicating that fixes may be pending or recently released. This vulnerability demands urgent attention from organizations relying on affected Mozilla products to prevent potential exploitation.

The vulnerability allows remote attackers to execute arbitrary code with the privileges of the user running Firefox or Thunderbird, potentially leading to full system compromise. This threatens confidentiality by enabling data theft, integrity by allowing unauthorized code execution or modification, and availability by causing crashes or denial of service. Since the attack requires only user interaction (such as visiting a malicious website or opening a malicious email), the attack surface is broad. Organizations using affected versions are at risk of targeted attacks, drive-by downloads, or phishing campaigns leveraging this flaw. The impact is especially critical for environments where Firefox or Thunderbird is used to access sensitive information or critical infrastructure. The lack of known exploits in the wild currently reduces immediate risk but does not eliminate the threat, as weaponization could occur rapidly after public disclosure. Failure to patch promptly could lead to widespread exploitation, data breaches, and operational disruption.

1. Immediately update Firefox and Thunderbird to versions 148 or later, or ESR versions 140.8 or later, once official patches are released by Mozilla. 2. Until patches are available, consider disabling WebAssembly execution in Firefox by setting 'javascript.options.wasm' to false in about:config to reduce attack surface. 3. Employ network-level protections such as web filtering and intrusion prevention systems to block access to known malicious sites or suspicious WebAssembly content. 4. Educate users to avoid clicking on untrusted links or opening suspicious emails, as exploitation requires user interaction. 5. Monitor security advisories from Mozilla and threat intelligence feeds for updates on exploit availability and mitigation guidance. 6. For high-security environments, consider using application sandboxing or endpoint protection solutions capable of detecting anomalous behavior related to memory corruption exploits. 7. Conduct regular vulnerability assessments and penetration tests focusing on browser and email client security to identify residual risks.