The vulnerability in the Hostel plugin arises from an improper handling of user inputs, particularly within the 'shortcode_id' parameter. Reflected XSS occurs when malicious scripts are reflected off a web application to the user's browser, thus executing in the context of the application's domain. This problem stems from the fact that the plugin fails to adequately sanitize and escape inputs, allowing malicious payloads to be injected and executed. Exploitation of this vulnerability requires social engineering techniques, such as tricking a user into clicking a specially designed link. If successful, the attacker could perform actions on behalf of the victim, potentially stealing sensitive information or performing unauthorized actions. Since this vulnerability affects all versions up to and including 1.1.6, it broadly impacts sites using unpatched versions of the plugin.

Site administrators should implement strong security policies to prevent such attacks, including educating users about the risks of clicking unknown links. Additionally, utilizing a web application firewall (WAF) can help protect against XSS attacks by blocking malicious requests. It is also advisable to use security plugins that provide additional input validation and output escaping functions.