osCommerce is prone to a local file-include vulnerability and an HTML-injection vulnerability because it fails to properly sanitize user-supplied input.
An attacker can exploit the local file-include vulnerability using directory-traversal strings to execute local files within the context of the webserver process.
The attacker may leverage the HTML-injection issue to execute arbitrary HTML and script code in the context of the affected browser. This may let the attacker steal cookie-based authentication credentials or control how the site is rendered to the user.
osCommerce 3.0a5 is affected; other versions may also be vulnerable.