filter通过装饰者模式防止XSS攻击

spring boot / cloud (一) 使用filter防止XSS

##一.前言

###XSS(跨站脚本攻击) >跨站脚本攻击(Cross Site Scripting)，为不和层叠样式表(Cascading Style Sheets, CSS)的缩写混淆，故将跨站脚本攻击缩写为XSS。恶意攻击者往Web页面里插入恶意Script代码，当用户浏览该页之时，嵌入其中Web里面的Script代码会被执行，从而达到恶意攻击用户的目的。

##二.思路

###基于filter拦截,将特殊字符替换为html转意字符 (如: "<" 转意为 "<") , 需要拦截的点如下:

• 请求头 requestHeader

• 请求体 requestBody

• 请求参数 requestParameter

##三.实现

###1.创建XssHttpServletRequestWrapper类

在获取请求头,请求参数的这些地方,将目标值使用HtmlUtils.htmlEscape方法转意为html字符,而避免恶意代码参与到后续的流程中

/** * XssHttpServletRequestWrapper.java * Created at 2016-09-19 * Created by wangkang * Copyright (C) 2016 egridcloud.com, All rights reserved. */package com.egridcloud.udf.core.xss;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletRequestWrapper;import org.springframework.web.util.HtmlUtils;/** * 描述 : 跨站请求防范 * * @author wangkang * */public class XssHttpServletRequestWrapper extends HttpServletRequestWrapper {  /**   * 描述 : 构造函数   *   * @param request 请求对象   */  public XssHttpServletRequestWrapper(HttpServletRequest request) {    super(request);  }  @Override  public String getHeader(String name) {    String value = super.getHeader(name);    return HtmlUtils.htmlEscape(value);  }  @Override  public String getParameter(String name) {    String value = super.getParameter(name);    return HtmlUtils.htmlEscape(value);  }  @Override  public String[] getParameterValues(String name) {    String[] values = super.getParameterValues(name);    if (values != null) {      int length = values.length;      String[] escapseValues = new String[length];      for (int i = 0; i < length; i++) {        escapseValues[i] = HtmlUtils.htmlEscape(values[i]);      }      return escapseValues;    }    return super.getParameterValues(name);  }}

###2.创建XssStringJsonSerializer类

其次是涉及到json转换的地方,也一样需要进行转意,比如,rerquestBody,responseBody

/** * XssStringJsonSerializer.java * Created at 2016-09-19 * Created by wangkang * Copyright (C) 2016 egridcloud.com, All rights reserved. */package com.egridcloud.udf.core.xss;import java.io.IOException;import org.springframework.web.util.HtmlUtils;import com.fasterxml.jackson.core.JsonGenerator;import com.fasterxml.jackson.databind.JsonSerializer;import com.fasterxml.jackson.databind.SerializerProvider;/** * 描述 : 基于xss的JsonSerializer * * @author wangkang * */public class XssStringJsonSerializer extends JsonSerializer<String> {  @Override  public Class<String> handledType() {    return String.class;  }  @Override  public void serialize(String value, JsonGenerator jsonGenerator,      SerializerProvider serializerProvider) throws IOException {    if (value != null) {      String encodedValue = HtmlUtils.htmlEscape(value);      jsonGenerator.writeString(encodedValue);    }  }}

###3.创建Bean

在启动类中,创建XssObjectMapper的bean,替换spring boot原有的实例,用于整个系统的json转换.

  /**   * 描述 : xssObjectMapper   *   * @param builder builder   * @return xssObjectMapper   */  @Bean  @Primary  public ObjectMapper xssObjectMapper(Jackson2ObjectMapperBuilder builder) {    //解析器    ObjectMapper objectMapper = builder.createXmlMapper(false).build();    //注册xss解析器    SimpleModule xssModule = new SimpleModule("XssStringJsonSerializer");    xssModule.addSerializer(new XssStringJsonSerializer());    objectMapper.registerModule(xssModule);    //返回    return objectMapper;  }

###4.创建XssFilter

首先是拦截所有的请求,然后在doFilter方法中,将HttpServletRequest强制类型转换成XssHttpServletRequestWrapper

然后传递下去.

/** * XssFilter.java * Created at 2016-09-19 * Created by wangkang * Copyright (C) 2016 egridcloud.com, All rights reserved. */package com.egridcloud.udf.core.xss;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.annotation.WebFilter;import javax.servlet.http.HttpServletRequest;import org.slf4j.Logger;import org.slf4j.LoggerFactory;/** * 描述 : 跨站请求防范 * * @author wangkang * */@WebFilter(filterName = "xssFilter", urlPatterns = "/*", asyncSupported = true)public class XssFilter implements Filter {  /**   * 描述 : 日志   */  private static final Logger LOGGER = LoggerFactory.getLogger(XssFilter.class);  @Override  public void init(FilterConfig filterConfig) throws ServletException {    LOGGER.debug("(XssFilter) initialize");  }  @Override  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)      throws IOException, ServletException {    XssHttpServletRequestWrapper xssRequest =        new XssHttpServletRequestWrapper((HttpServletRequest) request);    chain.doFilter(xssRequest, response);  }  @Override  public void destroy() {    LOGGER.debug("(XssFilter) destroy");  }}

##四.结束

本文虽基于spring boot实现主题,但是思路是一致的,不限于任何框架