CVE-2026-18431: Avada WordPress Theme RCE Vulnerability

CVE-2026-18431 Overview

The Avada theme for WordPress contains an unauthenticated arbitrary file write vulnerability when paired with the Fusion Builder plugin. The flaw affects Avada versions up to and including 7.16 and Fusion Builder versions up to and including 3.16. A chain of authorization and input validation weaknesses across both components allows attackers to write attacker-controlled files to the server. Successful exploitation lets an attacker create and execute arbitrary PHP files, leading to remote code execution and full site compromise. Exploitation requires both plugins to be installed and active, along with specific administrator-authored content on the site.

Critical Impact
Unauthenticated attackers can write arbitrary PHP files to vulnerable WordPress sites and achieve remote code execution, resulting in complete site takeover.

Affected Products

Avada theme for WordPress (versions up to and including 7.16)
Fusion Builder plugin for WordPress (versions up to and including 3.16)
WordPress installations running both components with qualifying administrator-authored content

Discovery Timeline

2026-08-26 - CVE-2026-18431 published to NVD
2026-08-26 - Last updated in NVD database

Technical Details for CVE-2026-18431

Vulnerability Analysis

The vulnerability is classified as Missing Authorization [CWE-862] combined with input validation weaknesses. It spans two tightly coupled WordPress components: the Avada theme and the Fusion Builder plugin. Neither component individually enforces sufficient authorization checks on file-handling operations exposed through the shared builder workflow.

An unauthenticated attacker can chain the weaknesses to submit a request that instructs the server to write a file whose path and contents the attacker controls. Because WordPress executes PHP files placed under the web root, the attacker can drop a PHP payload and request it directly to gain code execution under the web server user.

Exploitation depends on the presence of certain administrator-authored content, such as builder elements or templates that expose the vulnerable code path. Once those preconditions are met, the attack requires no authentication and no user interaction.

Root Cause

The root cause is a missing authorization check on file-writing functionality shared between the Avada theme and Fusion Builder plugin. Input validation on file paths and content is also insufficient, allowing attacker-controlled data to reach filesystem write operations.

Attack Vector

The attack is network-based over HTTP or HTTPS against the WordPress front end. An attacker sends a crafted request that triggers the vulnerable builder code path, writes a PHP file into a web-accessible directory, and then requests that file to execute the payload.

No verified public exploit code is available at the time of publication. Refer to the Wordfence Vulnerability Report for technical details.

Detection Methods for CVE-2026-18431

Indicators of Compromise

Unexpected .php files appearing in wp-content/uploads/, Fusion Builder cache directories, or theme directories
Web server access logs showing POST requests to Fusion Builder AJAX endpoints from unauthenticated sessions followed by GET requests to newly created PHP files
Modified or newly created files in the Avada theme directory with recent timestamps that do not match update activity
Outbound connections from the web server to unfamiliar hosts shortly after suspicious POST requests

Detection Strategies

Monitor file integrity across wp-content/themes/Avada/, wp-content/plugins/fusion-builder/, and upload directories for new or modified PHP files
Alert on HTTP requests to admin-ajax.php or Fusion Builder endpoints with parameters referencing file paths or file extensions
Correlate unauthenticated POST requests targeting builder endpoints with subsequent execution of new PHP files

Monitoring Recommendations

Enable WordPress audit logging for file changes, plugin activity, and administrator content edits
Forward web server, PHP-FPM, and WordPress logs to a centralized analytics platform for correlation
Review Wordfence or equivalent web application firewall (WAF) telemetry for rules matching this vulnerability signature

How to Mitigate CVE-2026-18431

Immediate Actions Required

Update the Avada theme to a version later than 7.16 and Fusion Builder to a version later than 3.16 as soon as fixed releases are available from the vendor
Restrict access to WordPress administrative and builder endpoints using IP allowlists or a WAF until patches are applied
Audit the WordPress filesystem for unauthorized PHP files and remove any confirmed web shells
Rotate WordPress administrator credentials, API keys, and database passwords if compromise is suspected

Patch Information

Refer to the Avada Changelog Documentation for the fixed release notes and confirm both the Avada theme and the Fusion Builder plugin are upgraded together. Additional advisory details are available in the Wordfence Vulnerability Report.

Workarounds

Deactivate the Fusion Builder plugin until updated versions of both components can be installed
Remove or restrict administrator-authored builder content known to expose the vulnerable code path
Deploy WAF rules that block unauthenticated requests to Fusion Builder AJAX handlers and requests containing file path parameters
Enforce filesystem permissions that prevent the web server user from writing PHP files into web-accessible directories where feasible

bash

# Configuration example: harden write permissions on WordPress content directories
find /var/www/html/wp-content/uploads -type f -name "*.php" -print
chown -R root:www-data /var/www/html/wp-content/themes/Avada
find /var/www/html/wp-content/themes/Avada -type d -exec chmod 755 {} \;
find /var/www/html/wp-content/themes/Avada -type f -exec chmod 644 {} \;