CVE-2026-16654: CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in themefusion Avada (Fusion) Builder

CVE-2026-16654 is a stored cross-site scripting vulnerability in the Avada (Fusion) Builder WordPress plugin. It occurs due to insufficient input sanitization and output escaping of the 'size' shortcode attribute in all versions up to 3.15.6. Authenticated attackers with contributor-level privileges or higher can inject arbitrary scripts that execute in the context of users viewing the compromised pages. The WordPress wp_kses_post filter fails to neutralize this payload because the malicious content is embedded entirely within a shortcode attribute string lacking HTML angle brackets, allowing it to bypass filtering at save time.

An attacker with contributor-level or higher access can inject persistent malicious scripts into pages, which execute in the browsers of users who view those pages. This can lead to theft of user credentials, session hijacking, or other actions permitted by the victim's browser context. The vulnerability does not affect availability but impacts confidentiality and integrity.

No official fix or patch is currently available for this vulnerability. Users should monitor the vendor's advisory for updates. Until a patch is released, restrict contributor-level access to trusted users only and consider removing or disabling the affected shortcode if possible.