The Optimole – Optimize Images | Convert WebP & AVIF | CDN & Lazy Load | Image Optimization plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 's (missing_srcsets[][].s)' parameter in all versions up to, and including, 4.2.18 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The HMAC signature required to pass the REST endpoint's authorization check is published in plaintext to unauthenticated visitors inside the inline optimoleDataOptimizer JavaScript object on any page with an incomplete profile, making the effective authentication barrier nonexistent.