防范XSS跨站2

原文:http://blog.csdn.net/joeyon1985/article/details/43527987

在前面的一篇文章中，讲到了java web应用程序防止 csrf 攻击的方法，参考这里 java网页程序采用 spring 防止 csrf 攻击.,但这只是攻击的一种方式，还有其他方式，比如今天要记录的 XSS 攻击， XSS 攻击的专业解释，可以在网上搜索一下，参考百度百科的解释 http://baike.baidu.com/view/2161269.htm, 但在实际的应用中如何去防止这种攻击呢，下面给出几种办法.
1. 自己写 filter 拦截来实现，但要注意的时，在WEB.XML 中配置 filter 的时候，请将这个 filter 放在第一位.
2. 采用开源的实现 ESAPI library ，参考网址:https://www.owasp.org/index.php/Category:OWASP_Enterprise_Security_API

3. 可以采用spring 里面提供的工具类来实现.

一， 第一种方法。
配置过滤器

public class XSSFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }
    @Override
    public void destroy() {
    }
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
        throws IOException, ServletException {
        chain.doFilter(new XSSRequestWrapper((HttpServletRequest) request), response);
    }
}

再实现 ServletRequest 的包装类

import java.util.regex.Pattern;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
public class XSSRequestWrapper extends HttpServletRequestWrapper {
    public XSSRequestWrapper(HttpServletRequest servletRequest) {
        super(servletRequest);
    }
    @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);
    }
    private String stripXSS(String value) {
        if (value != null) {
            // NOTE: It's highly recommended to use the ESAPI library and uncomment the following line to
            // avoid encoded attacks.
            // value = ESAPI.encoder().canonicalize(value);
            // Avoid null characters
            value = value.replaceAll("", "");
            // Avoid anything between script tags
            Pattern scriptPattern = Pattern.compile("(.*?)", Pattern.CASE_INSENSITIVE);
            value = scriptPattern.matcher(value).replaceAll("");
            // Avoid anything in a src="http://www.yihaomen.com/article/java/..." type of 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  tag
            scriptPattern = Pattern.compile("", Pattern.CASE_INSENSITIVE);
            value = scriptPattern.matcher(value).replaceAll("");
            // Remove any lonesome  tag
            scriptPattern = Pattern.compile("", 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("");
        }
        return value;
    }
}

例子中注释的部分，就是采用 ESAPI library 来防止XSS攻击的，推荐使用.

当然，我还看到这样一种办法，将所有的编程全角字符的解决方式，但个人觉得并没有上面这种用正则表达式替换的好

private static String xssEncode(String s) {
        if (s == null || s.equals("")) {
            return s;
        }
        StringBuilder sb = new StringBuilder(s.length() + 16);
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            switch (c) {
            case '>':
                sb.append('＞');// 全角大于号
                break;
            case '<':
                sb.append('＜');// 全角小于号
                break;
            case '\'':
                sb.append('\\');
                sb.append('\'');
                sb.append('\\');
                sb.append('\'');
                break;
            case '\"':
                sb.append('\\');
                sb.append('\"');// 全角双引号
                break;
            case '&':
                sb.append('＆');// 全角
                break;
            case '\\':
                sb.append('＼');// 全角斜线
                break;
            case '#':
                sb.append('＃');// 全角井号
                break;
            case ':':
                sb.append('：');// 全角冒号
                break;
            case '%':
                sb.append("\\\\%");
                break;
            default:
                sb.append(c);
                break;
            }
        }
        return sb.toString();
    }

当然，还有如下更简单的方式:

private String cleanXSS(String value) {
                //You'll need to remove the spaces from the html entities below
        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;
    }

在后台或者用spring 如何实现呢:
首先添加一个jar包：commons-lang-2.5.jar ，然后在后台调用这些函数：

StringEscapeUtils.escapeHtml(string);
StringEscapeUtils.escapeJavaScript(string);
StringEscapeUtils.escapeSql(string);

当然，我记得在spring 里面好像有一个 HtmlUtils.htmlEscape , 同样可以做到 过滤 XSS 攻击。从上面的介绍可以看出，防止 XSS 攻击并不难，就是要小心。