HTTP headers play a significant role in modern web security by providing browsers with specific instructions to adhere to certain security rules, instructing them to respond to various attacks and prevent sensitive data from being accessed. Headers such as HTTP Strict Transport Security (HSTS), X-Frame-Options, Content-Security-Policy (CSP), referrer-policy, Cache-Control, Feature Policy, and X-Content-Type-Options can be used to defend against man-in-the-middle attacks, clickjacking, cross-site scripting (XSS) attacks, information leakage, and content sniffing. By adding these custom headers to server responses, developers can improve the security of their websites and protect sensitive data from being accessed by attackers.