java 防止 XSS 攻擊的常用方法

1. 自己寫 filter 攔截來實現，但要註意的時，在WEB.XML 中配置 filter 的時候，請將這個 filter 放在第一位.
2. 採用開源的實現 ESAPI library ，參考網址: https://www.owasp.org/index.php/Category:OWASP_Enterprise_Security_API

3. 可以採用spring 裡面提供的工具類來實現.

一， 第一種方法。
web.xml文件Filter配置

<!-- 配置防SQL註入過濾器 -->
    <filter>
        <filter-name>XssFilter</filter-name>
        <filter-class>新編寫XssFilter路徑</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>XssFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

編寫Filter過濾器

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);
    }
}

再實現 ServletRequest 的包裝類

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("<script>(.*?)</script>", Pattern.CASE_INSENSITIVE);
            value = scriptPattern.matcher(value).replaceAll("");
            // Avoid anything in a src="..." 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 </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("");
        }
        return value;
    }
}

例子中註釋的部分，就是採用 ESAPI library 來防止XSS攻擊的，推薦使用.

當然，我還看到這樣一種辦法，將所有的編程全形字元的解決方式，但個人覺得並沒有上面這種用正則表達式替換的好

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('＞');// 全形大於號
                break;
            case '<':
                sb.append('＜');// 全形小於號
                break;
            case '\'':
                sb.append('\\');
                sb.append('\'');
                sb.append('\\');
                sb.append('\'');
                break;
            case '\"':
                sb.append('\\');
                sb.append('\"');// 全形雙引號
                break;
            case '&':
                sb.append('＆');// 全形
                break;
            case '\\':
                sb.append('＼');// 全形斜線
                break;
            case '#':
                sb.append('＃');// 全形井號
                break;
            case ':':
                sb.append('：');// 全形冒號
                break;
            case '%':
                sb.append("\\\\%");
                break;
            default:
                sb.append(c);
                break;
            }
        }
        return sb.toString();
    }

當然，還有如下更簡單的方式:

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;
    }

在後臺或者用spring 如何實現呢:
首先添加一個jar包：commons-lang-2.5.jar ，然後在後臺調用這些函數：

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

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