Input validation vulnerability in SendPress Newsletters 1.22.3.31

The SendPress Newsletters plugin for WordPress has a security vulnerability that allows attackers with contributor-level permissions and higher to inject malicious code into pages. If someone visits one of these pages, the malicious code will get executed. This vulnerability affects all versions of the plugin up until version 1.22.3.31, since it does not adequately sanitize user input or properly escape output.