利用过滤器防止XSS攻击

为什么80%的码农都做不了架构师？>>>   

一、首先科普点知识

（一）什么是XSS？

xss又叫CSS(Cross-SiteScripting),跨站脚本攻击。恶意攻击者往Web页面里插入恶意html代码，当用户浏览该页之时，嵌入其中Web里面的html代码会被执行，从而达到恶意用户的特殊目的。主要指的自己构造XSS跨站漏洞网页或者寻找非目标机以外的有跨站漏洞的网页。

（二）Java中拦截器与过滤器的差异：

1、拦截器是基于java反射机制的，而过滤器是基于函数回调的。

2、过滤器依赖于servlet容器，而拦截器不依赖于servlet容器。

3、拦截器只对action起作用，而过滤器几乎可以对所有请求起作用。

4、拦截器可以访问action上下文、值栈里的对象，而过滤器不能。

5、在action的生命周期里，拦截器可以多起调用，而过滤器只能在容器初始化时调用一次。

二、写过滤器实现过滤

（一）首先自己写一个过滤器

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

public class XSSFilter implements Filter {  
  
    @Override  
    public void destroy() {  
        // TODO Auto-generated method stub  
  
    }  
  
    @Override  
    public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)  
            throws IOException, ServletException {  
        // TODO Auto-generated method stub  
        arg2.doFilter(new XSSRequestWrapper((HttpServletRequest) arg0), arg1);  
    }  
  
    @Override  
    public void init(FilterConfig arg0) throws ServletException {  
        // TODO Auto-generated method stub  
  
    }  
  
}  

（二）然后写一个自己用来实现业务的HttpServletRequestWrapper

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.util.regex.Pattern;


public class XSSRequestWrapper extends HttpServletRequestWrapper {

    public XSSRequestWrapper(HttpServletRequest request) {
        super(request);
    }

    @Override
    public String[] getParameterValues(String parameter) {
        String[] values = super.getParameterValues(parameter);
        if (values == null) {
            return null;
        }
        int count = values.length;
        String[] encodedValues = new String[count];
        for (int i = 0; i < count; i++) {
            encodedValues[i] = stripXSS(values[i]);
        }
        return encodedValues;
    }

    @Override
    public String getParameter(String parameter) {
        String value = super.getParameter(parameter);
        return stripXSS(value);
    }

    @Override
    public String getHeader(String name) {
        String value = super.getHeader(name);
        //return stripXSS(value);
        return value;
    }

    public String getQueryString() {
        String value = super.getQueryString();
        if (value != null) {
            value = stripXSS(value);
        }
        return value;
    }

    private String stripXSS(String value) {
        if (value != null) {
            // Avoid anything between script tags
            Pattern scriptPattern = Pattern.compile("<script>(.*?)</script>", Pattern.CASE_INSENSITIVE);
            value = scriptPattern.matcher(value).replaceAll("");
            // Avoid anything in a
            // e­xpression
            scriptPattern = Pattern.compile("src[\r\n]*=[\r\n]*\\\'(.*?)\\\'",
                    Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL);
            value = scriptPattern.matcher(value).replaceAll("");
            scriptPattern = Pattern.compile("src[\r\n]*=[\r\n]*\\\"(.*?)\\\"",
                    Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL);
            value = scriptPattern.matcher(value).replaceAll("");
            // Remove any lonesome </script> tag
            scriptPattern = Pattern.compile("</script>", Pattern.CASE_INSENSITIVE);
            value = scriptPattern.matcher(value).replaceAll("");
            // Remove any lonesome <script ...> tag
            scriptPattern = Pattern.compile("<script(.*?)>",
                    Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL);
            value = scriptPattern.matcher(value).replaceAll("");
            // Avoid eval(...) e­xpressions
            scriptPattern = Pattern.compile("eval\\((.*?)\\)",
                    Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL);
            value = scriptPattern.matcher(value).replaceAll("");
            // Avoid e­xpression(...) e­xpressions
            scriptPattern = Pattern.compile("e­xpression\\((.*?)\\)",
                    Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL);
            value = scriptPattern.matcher(value).replaceAll("");
            // Avoid javascript:... e­xpressions
            scriptPattern = Pattern.compile("javascript:", Pattern.CASE_INSENSITIVE);
            value = scriptPattern.matcher(value).replaceAll("");
            // Avoid vbscript:... e­xpressions
            scriptPattern = Pattern.compile("vbscript:", Pattern.CASE_INSENSITIVE);
            value = scriptPattern.matcher(value).replaceAll("");
            // Avoid onload= e­xpressions
            scriptPattern = Pattern.compile("onload(.*?)=",
                    Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL);
            value = scriptPattern.matcher(value).replaceAll("");

            /*过滤html标签*/
            Pattern p_html = Pattern.compile("<[^>]+>", Pattern.CASE_INSENSITIVE);
            value = p_html.matcher(value).replaceAll("");
            Pattern p_html1 = Pattern.compile("<[^>]+", Pattern.CASE_INSENSITIVE);
            value = p_html1.matcher(value).replaceAll("");

        }
        return value;
    }
}

（三）最后在web.xml中进行配置

<filter>
		<filter-name>XSSFilter</filter-name>
		<filter-class></filter-class>
	</filter>
	<filter-mapping>
		<filter-name>XSSFilter</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>

完事！

转载于:https://my.oschina.net/ayo123/blog/1540630