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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
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
scriptPattern = Pattern.compile("
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 οnlοad= 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。
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