Sarah, a web security analyst, receives a report that a certain page on the company's website is vulnerable to an XSS attack. She decides to implement a CSP. Which of the following directives should she prioritize to mitigate this specific threat?

To mitigate the threat of XSS (Cross-Site Scripting) attacks, Sarah should prioritize the script-src directive when implementing a CSP. This directive controls which scripts are allowed to execute on a web page, and by restricting this, she can mitigate the risk of malicious script execution.