Java实现XSS防御

XSS概述

跨站脚本攻击(Cross Site Scripting)，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。

Servlet的方式

1、继承HttpServletRequestWrapper，实现对请求参数的过滤

/**
 * xss请求适配器
 */
public class XssHttpServletRequestWrapper extends HttpServletRequestWrapper {

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

    /**
     * 对数组参数进行特殊字符过滤
     */
    @Override
    public String[] getParameterValues(String name) {
        String[] values = super.getParameterValues(name);
        if (values == null) {
            return null;
        }
        int count = values.length;
        String[] encodedValues = new String[count];
        for (int i = 0; i < count; i++) {
            encodedValues[i] = cleanXSS(values[i]);
        }
        return encodedValues;
    }

    /**
     * 对参数中特殊字符进行过滤
     */
    @Override
    public String getParameter(String name) {
        String value = super.getParameter(name);
        if (value == null) {
            return null;
        }
        return cleanXSS(value);
    }

    /**
     * 获取attribute,特殊字符过滤
     */
    @Override
    public Object getAttribute(String name) {
        Object value = super.getAttribute(name);
        if (value != null && value instanceof String) {
            cleanXSS((String) value);
        }
        return value;
    }

    /**
     * 对请求头部进行特殊字符过滤
     */
    @Override
    public String getHeader(String name) {
        String value = super.getHeader(name);
        if (value == null) {
            return null;
        }
        return cleanXSS(value);
    }

    /**
     * 转义字符,使用该方法存在一定的弊端
     * 
     * @param value
     * @return
     */
    private String cleanXSS2(String value) {
        // 移除特殊标签
        value = value.replaceAll("<", "&lt;").replaceAll(">", "&gt;");
        value = value.replaceAll("\\(", "&#40;").replaceAll("\\)", "&#41;");
        value = value.replaceAll("'", "&#39;");
        value = value.replaceAll("eval\\((.*)\\)", "");
        value = value.replaceAll("[\\\"\\\'][\\s]*javascript:(.*)[\\\"\\\']", "\"\"");
        value = value.replaceAll("script", "");
        return value;
    }

    private String cleanXSS(String value) {
        if (value != null) {
            //推荐使用ESAPI库来避免脚本攻击,value = ESAPI.encoder().canonicalize(value);
            // 避免空字符串
            value = value.replaceAll(" ", "");
            // 避免script 标签
            Pattern scriptPattern = Pattern.compile("<script>(.*?)</script>", Pattern.CASE_INSENSITIVE);
            value = scriptPattern.matcher(value).replaceAll("");
            // 避免src形式的表达式
            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("");
            // 删除单个的 </script> 标签
            scriptPattern = Pattern.compile("</script>", Pattern.CASE_INSENSITIVE);
            value = scriptPattern.matcher(value).replaceAll("");
            // 删除单个的<script ...> 标签
            scriptPattern = Pattern.compile("<script(.*?)>",
                    Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL);
            value = scriptPattern.matcher(value).replaceAll("");
            // 避免 eval(...) 形式表达式
            scriptPattern = Pattern.compile("eval\\((.*?)\\)",
                    Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL);
            value = scriptPattern.matcher(value).replaceAll("");
            // 避免 e­xpression(...) 表达式
            scriptPattern = Pattern.compile("e­xpression\\((.*?)\\)",
                    Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL);
            value = scriptPattern.matcher(value).replaceAll("");
            // 避免 javascript: 表达式
            scriptPattern = Pattern.compile("javascript:", Pattern.CASE_INSENSITIVE);
            value = scriptPattern.matcher(value).replaceAll("");
            // 避免 vbscript:表达式
            scriptPattern = Pattern.compile("vbscript:", Pattern.CASE_INSENSITIVE);
            value = scriptPattern.matcher(value).replaceAll("");
            // 避免 onload= 表达式
            scriptPattern = Pattern.compile("onload(.*?)=",
                    Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL);
            value = scriptPattern.matcher(value).replaceAll("");
        }
        return value;
    }

}

2、实现Filter，实现XSS过滤器

/**
 * xss过滤器
 */
public class XssFilter implements Filter {

    FilterConfig filterConfig = null;

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        this.filterConfig = filterConfig;
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        //对请求进行拦截,防xss处理
        chain.doFilter(new XssHttpServletRequestWrapper((HttpServletRequest) request), response);
    }

    @Override
    public void destroy() {
        this.filterConfig = null;
    }

}

3、注入XSS过滤器，两种方式 
第一种方式：配置web.xml

<!-- xss过滤器 -->
<filter>
    <filter-name>XssSqlFilter</filter-name>
    <filter-class>cn.aric.xss.XssFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>XssSqlFilter</filter-name>
    <url-pattern>/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
    <dispatcher>FORWARD</dispatcher>
</filter-mapping>

第二种方式：注解

/**
 * 注入Xss过滤器(注解方式)
 */
public class WebInitializer implements WebApplicationInitializer{

    @Override
    public void onStartup(ServletContext servletContext) throws ServletException {
        //添加监听器
        servletContext.addListener(RequestContextListener.class);
        //添加过滤器
        Dynamic xssFilterRegistration = servletContext.addFilter("XssFilter", XssFilter.class);
        //添加映射规则
        xssFilterRegistration.addMappingForUrlPatterns(
                EnumSet.of(DispatcherType.REQUEST,DispatcherType.FORWARD,DispatcherType.INCLUDE), 
                false, 
                "/*");

    }

}

Spring整合的方式

1、使用spring的HtmlUtils,可以使用StringEscapeUtils 中的过滤方法

/**
 * 解决XSS跨站脚本攻击和sql注入攻击,使用spring的HtmlUtils,可以使用StringEscapeUtils 中的过滤方法
 */
public class XssSpringHttpServletRequestWrapper extends HttpServletRequestWrapper{

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

    /**
     * 对数组参数进行特殊字符过滤
     */
    @Override
    public String[] getParameterValues(String name) {
        String[] values = super.getParameterValues(name);
        String[] newValues = new String[values.length];
        for (int i = 0; i < values.length; i++) {
            //spring的HtmlUtils进行转义
            newValues[i] = HtmlUtils.htmlEscape(values[i]);
        }
        return newValues;
    }

    /**
     * 拦截参数,并对其进行字符转义
     */
    @Override
    public String getParameter(String name) {
        return HtmlUtils.htmlEscape(name);
    }

    /**
     * 拦截参数,并对其进行字符转义
     */
    @Override
    public Object getAttribute(String name) {
        return HtmlUtils.htmlEscape(name);
    }

}

2、实现XSS过滤器

/**
 * spring方式xss过滤器
 */
public class XssSpringFilter implements Filter{

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) request;
        chain.doFilter(new XssSpringHttpServletRequestWrapper(req), response);
    }

    @Override
    public void destroy() {

    }

}

3、配置XSS过滤器

<!-- spring方式的xss过滤器 -->
<filter>
    <filter-name>xssSpringFilter</filter-name>
    <filter-class>cn.aric.xss.XssSpringHttpServletRequestWrapper</filter-class>
</filter>
<filter-mapping>
    <filter-name>xssSpringFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>