WordPress 4.5.2 – a security release – is just released tonight. WordPress 4.5.2 fixes a vulnerability through Plupload, the third-party library WordPress uses for uploading files.
WordPress versions 4.2 through 4.5.1 are vulnerable to reflected XSS using specially crafted URIs through MediaElement.js, the third-party library used for media players. MediaElement.js and Plupload have also released updates fixing these issues.
As said, WordPress 4.5.2 is now available. This is a security release for all previous versions and we strongly encourage you to update your sites immediately.