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springboot2.x使用Jsoup防XSS攻击的实现

后端应用经常接收各种信息参数，例如评论，回复等文本内容。除了一些场景下面，可以特定接受的富文本标签和属性之外(如:b,ul,li,h1, h2, h3...),需要过滤掉危险的字符和标签，防止xss攻击。

一、什么是XSS?

看完这个，应该有一个大致的概念。

XSS攻击常识及常见的XSS攻击脚本汇总
XSS过滤速查表

二、准则

  • 永远不要相信用户的输入和请求的参数(包括文字、上传等一切内容)
  • 参考第1条

三、实现做法

结合具体业务场景，对相应内容进行过滤，这里使用Jsoup。

jsoup是一款Java的HTML解析器。Jsoup提供的Whitelist(白名单)对文本内容进行过滤，过滤掉字符、属性，但是又保留必要的富文本格式。
如，白名单中允许b标签存在（并且不允许b标签带有其他属性）那么在一段Html内容，在过滤之后，会变成：

过滤前：

<b style="xxx" onclick="<script>alert(0);</script>">abc</>

过滤后： 

<b>abc</b>

Whitelist主要方法说明

方法 说明
addAttributes(String tag, String... attributes) 给标签添加属性。Tag是属性名，keys对应的是一个个属性值。例如：addAttributes("a", "href", "class")表示：给标签a添加href和class属性，即允许标签a包含href和class属性。如果想给每一个标签添加一组属性，使用:all。例如：addAttributes(":all", "class").即给每个标签添加class属性。
addEnforcedAttribute(String tag, String attribute, String value) 给标签添加强制性属性，如果标签已经存在了要添加的属性，则覆盖原有值。tag:标签；key：标签的键；value：标签的键对应的值。例如：addEnforcedAttribute("a", "rel", "nofollow")表示
addProtocols(String tag, String key, String...protocols) 给URL属性添加协议。例如：addProtocols("a", "href", "ftp", "http", "https")标签a的href键可以指向的协议有ftp、http、https
addTags(String... tags) 向Whitelist添加标签
basic() 允许的标签包括： a, b, blockquote, br, cite, code, dd, dl, dt, em, i, li, ol, p, pre, q, small, strike, strong, sub, sup, u, ul,以及合适的属性。标签a指向的连接可以是 http, https, ftp, mailto，转换完后会强制添加 rel=nofollow这个属性。不允许包含图片。
basicWithImages() 在basic的基础上增加了图片的标签：img以及使用src指向http或https类型的图片链接。
none() 只保留文本，其他所有的html内容均被删除
preserveRelativeLinks(booleanpreserve) false（默认）：不保留相对地址的url；true：保留相对地址的url
relaxed() 允许的标签:a, b, blockquote, br, caption, cite, code, col, colgroup, dd, dl, dt, em, h1, h2, h3, h4, h5, h6, i, img, li, ol, p, pre, q, small, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, u, ul。结果不包含标签rel=nofollow，如果需要可以手动添加。
simpleText() 只允许:b, em, i, strong, u。

四、例子

基于springboot

pom.xml依赖

<dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
    </dependency>

    <!-- jsoup -->
    <dependency>
      <groupId>org.jsoup</groupId>
      <artifactId>jsoup</artifactId>
      <version>1.13.1</version>
    </dependency>

    <dependency>
      <groupId>org.apache.commons</groupId>
      <artifactId>commons-lang3</artifactId>
    </dependency>

    <dependency>
      <groupId>commons-io</groupId>
      <artifactId>commons-io</artifactId>
      <version>2.6</version>
    </dependency>

  </dependencies>

HtmlFilter过滤类

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.safety.Whitelist;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.List;

/**
 * HtmlFilter
 *
 * @author 撸小鱼
 * Created by lofish@foxmail.com on 2020-04-12
 */
public class HtmlFilter {

  /**
   * 默认使用relaxed()
   * 允许的标签: a, b, blockquote, br, caption, cite, code, col, colgroup, dd, dl, dt, em, h1, h2, h3, h4, h5, h6, i, img, li, ol, p, pre, q, small, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, u, ul。结果不包含标签rel=nofollow ，如果需要可以手动添加。
   */
  private Whitelist whiteList;


  /**
   * 配置过滤化参数,不对代码进行格式化
   */
  private Document.OutputSettings outputSettings;


  private HtmlFilter() {
  }

  /**
   * 静态创建HtmlFilter方法
   * @param whiteList 白名单标签
   * @param pretty 是否格式化
   * @return HtmlFilter
   */
  public static HtmlFilter create(Whitelist whiteList, boolean pretty) {
    HtmlFilter filter = new HtmlFilter();
    if (whiteList == null) {
      filter.whiteList = Whitelist.relaxed();
    }
    filter.outputSettings = new Document.OutputSettings().prettyPrint(pretty);
    return filter;
  }

  /**
   * 静态创建HtmlFilter方法
   * @return HtmlFilter
   */
  public static HtmlFilter create() {
    return create(null, false);
  }

  /**
   * 静态创建HtmlFilter方法
   * @param whiteList 白名单标签
   * @return HtmlFilter
   */
  public static HtmlFilter create(Whitelist whiteList) {
    return create(whiteList, false);
  }

  /**
   * 静态创建HtmlFilter方法
   * @param excludeTags 例外的特定标签
   * @param includeTags 需要过滤的特定标签
   * @param pretty   是否格式化
   * @return HtmlFilter
   */
  public static HtmlFilter create( List<String> excludeTags,List<String> includeTags, boolean pretty) {
    HtmlFilter filter = create(null, pretty);
    //要过滤的标签
    if (includeTags != null && !includeTags.isEmpty()) {
      String[] tags = (String[]) includeTags.toArray(new String[0]);
      filter.whiteList.removeTags(tags);
    }
    //例外标签
    if (excludeTags != null && !excludeTags.isEmpty()) {
      String[] tags = (String[]) excludeTags.toArray(new String[0]);
      filter.whiteList.addTags(tags);
    }
    return filter;
  }


  /**
   * 静态创建HtmlFilter方法
   * @param excludeTags 例外的特定标签
   * @param includeTags 需要过滤的特定标签
   * @return HtmlFilter
   */
  public static HtmlFilter create(List<String> excludeTags,List<String> includeTags) {
    return create( includeTags, excludeTags, false );
  }

  /**
   * @param content 需要过滤内容
   * @return 过滤后的String
   */
  public String clean(String content) {
    return Jsoup.clean(content, "", this.whiteList, this.outputSettings);

  }

  public static void main(String[] args) throws FileNotFoundException, IOException {
    String text = "<a href=\"http://www.baidu.com/a\" onclick=\"alert(1);\"></a><script>alert(0);</script><b style=\"xxx\" onclick=\"<script>alert(0);</script>\">abc</>";
    System.out.println(HtmlFilter.create().clean(text));
  }
}

XssFilter过滤器

import org.apache.commons.lang3.StringUtils;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * XssFilter
 *
 * @author 撸小鱼
 * Created by lofish@foxmail.com on 2020-04-12
 */
public class XssFilter implements Filter {

  /**
   * 例外urls
   */
  private List<String> excludeUrls = new ArrayList<>();

  /**
   * 例外标签
   */
  private List<String> excludeTags = new ArrayList<>();

  /**
   * 需要过滤标签
   */
  private List<String> includeTags = new ArrayList<>();

  /**
   * 开关
   */
  public boolean enabled = false;

  /**
   * 编码
   */
  private String encoding = "UTF-8";

  @Override
  public void init(FilterConfig filterConfig) throws ServletException {
    String enabledStr = filterConfig.getInitParameter("enabled");
    String excludeUrlStr = filterConfig.getInitParameter("urlPatterns");
    String excludeTagStr = filterConfig.getInitParameter("excludes");
    String includeTagStr = filterConfig.getInitParameter("includes");
    String encodingStr = filterConfig.getInitParameter("encoding");

    if (StringUtils.isNotEmpty(excludeUrlStr)) {
      String[] url = excludeUrlStr.split(",");
      Collections.addAll(this.excludeUrls, url);
    }

    if (StringUtils.isNotEmpty(excludeTagStr)) {
      String[] url = excludeTagStr.split(",");
      Collections.addAll(this.excludeTags, url);
    }

    if (StringUtils.isNotEmpty(includeTagStr)) {
      String[] url = includeTagStr.split(",");
      Collections.addAll(this.includeTags, url);
    }

    if (StringUtils.isNotEmpty(enabledStr)) {
      this.enabled = Boolean.parseBoolean(enabledStr);
    }

    if (StringUtils.isNotEmpty(encodingStr)) {
      this.encoding = encodingStr;
    }

  }

  @Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    HttpServletRequest req = (HttpServletRequest) request;
    HttpServletResponse resp = (HttpServletResponse) response;
    if (handleExcludeUrls(req, resp)) {
      chain.doFilter(request, response);
      return;
    }

    XssHttpServletRequestWrapper xssRequest = new XssHttpServletRequestWrapper((HttpServletRequest) request, encoding, excludeTags, includeTags );
    chain.doFilter(xssRequest, response);

  }

  private boolean handleExcludeUrls(HttpServletRequest request, HttpServletResponse response) {
    if (!enabled) {
      return true;
    }
    if (excludeUrls == null || excludeUrls.isEmpty()) {
      return false;
    }
    String url = request.getServletPath();
    for (String pattern : excludeUrls) {
      Pattern p = Pattern.compile("^" + pattern);
      Matcher m = p.matcher(url);
      if (m.find()) {
        return true;
      }
    }
    return false;
  }
}

一般情况下，我们都是通过request的parameter来传递参数。
但是，如果在某些场景下面，通过requestBody体(json等)，来传递相应参数应该怎么办？
这就要需要我们对request的inputStream来进行来过滤处理了

有个地方需要注意一下的:
servlet中inputStream只能一次读取，后续不能再次读取inputStream。Xss过滤器中读取了stream之后，后续如果其他逻辑涉及到inputStream读取，会抛出异常。那我们就需要想办法把已经读取的stream，重新放回到请求中。

import org.apache.commons.io.IOUtils;
import org.apache.commons.lang3.StringUtils;

import javax.servlet.ReadListener;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;


/**
 * XSS过滤处理
 * @author 撸小鱼
 * Created by lofish@foxmail.com
 */
public class XssHttpServletRequestWrapper extends HttpServletRequestWrapper{

  HttpServletRequest orgRequest;

  String encoding;

  HtmlFilter htmlFilter;

  private final static String JSON_CONTENT_TYPE = "application/json";

  private final static String CONTENT_TYPE = "Content-Type";


  /**
   * @param request HttpServletRequest
   * @param encoding 编码
   * @param excludeTags 例外的特定标签
   * @param includeTags 需要过滤的标签
   */
  public XssHttpServletRequestWrapper( HttpServletRequest request, String encoding, List<String> excludeTags, List<String> includeTags ){
    super( request );
    orgRequest = request;
    this.encoding = encoding;
    this.htmlFilter = HtmlFilter.create( excludeTags, includeTags );
  }

  /**
   *
   * @param request HttpServletRequest
   * @param encoding 编码
   */
  public XssHttpServletRequestWrapper( HttpServletRequest request, String encoding ){
    this( request, encoding, null, null );
  }

  private String xssFilter( String input ){
    return htmlFilter.clean( input );
  }

  @Override
  public ServletInputStream getInputStream() throws IOException{
    // 非json处理
    if( !JSON_CONTENT_TYPE.equalsIgnoreCase( super.getHeader( CONTENT_TYPE ) ) ){
      return super.getInputStream();
    }
    InputStream in = super.getInputStream();
    String body = IOUtils.toString( in, encoding );
    IOUtils.closeQuietly( in );

    //空串处理直接返回
    if( StringUtils.isBlank( body ) ){
      return super.getInputStream();
    }

    // xss过滤
    body = xssFilter( body );
    return new RequestCachingInputStream( body.getBytes( encoding ) );

  }

  @Override
  public String getParameter( String name ){
    String value = super.getParameter( xssFilter( name ) );
    if( StringUtils.isNotBlank( value ) ){
      value = xssFilter( value );
    }
    return value;
  }

  @Override
  public String[] getParameterValues( String name ){
    String[] parameters = super.getParameterValues( name );
    if( parameters == null || parameters.length == 0 ){
      return null;
    }

    for( int i = 0; i < parameters.length; i++ ){
      parameters[i] = xssFilter( parameters[i] );
    }
    return parameters;
  }

  @Override
  public Map<String, String[]> getParameterMap(){
    Map<String, String[]> map = new LinkedHashMap<>();
    Map<String, String[]> parameters = super.getParameterMap();
    for( String key : parameters.keySet() ){
      String[] values = parameters.get( key );
      for( int i = 0; i < values.length; i++ ){
        values[i] = xssFilter( values[i] );
      }
      map.put( key, values );
    }
    return map;
  }

  @Override
  public String getHeader( String name ){
    String value = super.getHeader( xssFilter( name ) );
    if( StringUtils.isNotBlank( value ) ){
      value = xssFilter( value );
    }
    return value;
  }

  /**
   * <b>
   * #获取最原始的request
   * </b>
   */
  public HttpServletRequest getOrgRequest(){
    return orgRequest;
  }

  /**
   * <b>
   * #获取最原始的request
   * </b>
   * @param request HttpServletRequest
   */
  public static HttpServletRequest getOrgRequest( HttpServletRequest request ){
    if( request instanceof XssHttpServletRequestWrapper ){
      return ((XssHttpServletRequestWrapper) request).getOrgRequest();
    }
    return request;
  }

  /**
   * <pre>
   * servlet中inputStream只能一次读取，后续不能再次读取inputStream
   * xss过滤body后，重新把流放入ServletInputStream中
   * </pre>
   */
  private static class RequestCachingInputStream extends ServletInputStream {
    private final ByteArrayInputStream inputStream;
    public RequestCachingInputStream(byte[] bytes) {
      inputStream = new ByteArrayInputStream(bytes);
    }

    @Override
    public int read() throws IOException {
      return inputStream.read();
    }

    @Override
    public boolean isFinished() {
      return inputStream.available() == 0;
    }

    @Override
    public boolean isReady() {
      return true;
    }

    @Override
    public void setReadListener( ReadListener readListener ){
    }
  }
}

springboot2.2.4.RELEASE中注册Filter

@Configuration
public class XssFilterConfig {

  @Value("${xss.enabled:true}")
  private String enabled;

  @Value("${xss.excludes:}")
  private String excludes;

  @Value("${xss.includes$:}")
  private String includes;

  @Value("${xss.urlPatterns:/*}")
  private String urlPatterns;

  @Bean
  public FilterRegistrationBean<XssFilter> xssFilterRegistrationBean() {
    FilterRegistrationBean<XssFilter> registration = new FilterRegistrationBean<>();
    registration.setDispatcherTypes(DispatcherType.REQUEST);
    registration.setFilter(new XssFilter());
    registration.addUrlPatterns(urlPatterns.split(","));
    registration.setName("XssFilter");
    registration.setOrder(Integer.MAX_VALUE);
    Map<String, String> initParameters = new HashMap<String, String>();
    initParameters.put("excludes", excludes);
    initParameters.put("includes", excludes);
    initParameters.put("enabled", enabled);
    registration.setInitParameters(initParameters);
    return registration;
  }
}

测试

http://localhost:8080/demo/th/xss?abc=%3Ca%20href=%22http://www.baidu.com/a%22%20onclick=%22alert(1);%22%3Eabc%3C/a%3E%3Cscript%3Ealert(0);%3C/script%3E&abc=%3Cb%20style=%22xxx%22%20onclick=%22%3Cscript%3Ealert(0);%3C/script%3E%22%3Eabc%3C/%3E

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