The Social Share application is vulnerable to a cross-site scripting (XSS) attack due to inadequate input sanitization. An attacker can exploit this vulnerability by injecting malicious script code into the 'search' parameter of the 'search.php' page. When an unsuspecting user visits the affected page, the injected script code will be executed in their browser, potentially allowing the attacker to steal sensitive information such as authentication credentials and launch further attacks.