Input validation vulnerability in Optin Forms – Simple List Building Plugin for WordPress 1.3.3

The Optin Forms – Simple List Building Plugin for WordPress is vulnerable to a type of attack called Stored Cross-Site Scripting. This type of attack affects all versions of the plugin up to and including version 1.3.3. It can allow people with certain levels of access (administrator level or higher) to inject malicious code into webpages. When someone visits one of these pages, the code will be executed and can cause harm. This only affects WordPress installations that are on multi-site networks or that have disabled a security feature called Unfiltered HTML.