[Source] ASP.NET MVC requests XSS Dangerous Content Validation (ValidateInput)

Cross-site scripting (XSS) is a security vulnerability that can be found in some web applications. XSS attacks enable attackers to inject client-side scripts into web pages viewed by other users. Attackers could exploit cross-site scripting vulnerabilities to bypass access controls such as same-origin policies.

public void ValidateInput() {
            // It doesn't make sense to call this multiple times per request.
            // Additionally, if validation was suppressed, no-op now.
            if (ValidateInputWasCalled || RequestValidationSuppressed) {
                return;
            }

            _flags. Set(hasValidateInputBeenCalled);

            // This is to prevent some XSS (cross site scripting) attacks (ASURT 122278)
            _flags. Set(needToValidateQueryString);
            _flags. Set(needToValidateForm);
            _flags. Set(needToValidateCookies);
            _flags. Set(needToValidatePostedFiles);
            _flags. Set(needToValidateRawUrl);
            _flags. Set(needToValidatePath);
            _flags. Set(needToValidatePathInfo);
            _flags. Set(needToValidateHeaders);
        }

ValidateAntiForgeryToken and AutoValidateAntiforgeryToken anti-counterfeiting tags are explained in detail
https://www.itsvse.com/thread-9568-1-1.html