Inadequate input sanitization and output escaping in the Webling plugin's 'webling_admin_save_form' and 'webling_admin_save_memberlist' functions lead to this vulnerability. The lack of proper capability checks allows lower-privileged users, such as Subscribers, to exploit this flaw. By injecting arbitrary web scripts, attackers can execute these scripts in the context of an administrator's session. Such scripts can lead to a range of attacks, including session hijacking or defacement of admin content. The vulnerability poses a significant risk as it compromises the integrity and security of the WordPress admin interface. It is crucial for site administrators to address this issue promptly to prevent any malicious activities.

Ensure that input validation, sanitation, and output escaping are correctly implemented in the plugin. Limit the privileges of user roles and adhere to the principle of least privilege by reviewing and possibly restricting Subscriber-level access. Regularly audit plugins in use for vulnerabilities and apply security updates promptly.