Since Joomla 1.5 reached end-of-life in 2012, it is vulnerable. If possible, migrate to Joomla 4 or 5. For now, ensure your Facebook Like button does not load external scripts that could inject malicious code.
If you are still running a Joomla 1.5 site, you know the struggle: most modern plugins no longer support your version. Finding a dedicated "Facebook Like plugin" for Joomla 1.5 is nearly impossible today. facebook like plugin joomla 1.5
How to Add a Facebook Like Button to Joomla 1.5 (No Plugin Required) Since Joomla 1