The Brizy Page Builder plugin <= 2.3.11 for WordPress allowed authenticated users to upload executable files to a location of their choice using the brizy_create_block_screenshot AJAX action. The file would be named using the id parameter, which could be prepended with "../" to perform directory traversal, and the file contents were populated via the ibsf parameter, which would be base64-decoded and written to the file. While the plugin added a .jpg extension to all uploaded filenames, a double extension attack was still possible, e.g. a file named shell.php would be saved as shell.php.jpg, and would be executable on a number of common configurations.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-38346
• https://www.wordfence.com/blog/2021/10/multiple-vulnerabilities-in-brizy-page-builder-plugin-allow-site-takeover/