WP Photo Album Plus: authenticated command injection gives server code execution

The WP Photo Album Plus plugin for WordPress is vulnerable to authenticated Command Injection in all versions up to, and including, 9.3.02.002 via the value parameter of the update-photo AJAX action. This is due to insufficient shell escaping within the wppa_image_magick_a() function, where the attacker-controlled value parameter is concatenated raw — without escapeshellarg() — into an ImageMagick command string before being passed to exec(); further, wppa_decode() actively restores percent-encoded shell metacharacters (e.g., %26→&, %23→#) rather than stripping them, allowing crafted payloads to survive sanitization and break out of the ImageMagick argument context. This makes it possible for authenticated attackers holding the plugin-defined wppa_upload capability to execute arbitrary operating-system commands as the web-server user, achieving full remote code execution on the underlying server. Exploitation requires ImageMagick to be enabled on the server; the wppa_upload capability is a plugin-level privilege that site administrators may grant to lower-privileged WordPress roles via the plugin's Users settings, broadening the pool of potential attackers beyond administrators.