java XSS防护

1.什么是XSS攻击

xss表示Cross Site Scripting(跨站脚本攻击)，xss攻击通过插入恶意脚本，实现对用户游览器的控制。比较常见的是利用xss攻击获取session id从而获取网站用户权限。

2.如何防护

这里介绍一种使用过滤器防护的方法。使用Filter对用户提交的数据进行过滤处理，去除恶意脚本。

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);
}
}

public class XSSRequestWrapper extends HttpServletRequestWrapper {
public XSSRequestWrapper(HttpServletRequest servletRequest) {
super(servletRequest);
}

@Override
public Map<String, String[]> getParameterMap() {
// 参数Map
Map properties = super.getParameterMap();
// 返回值Map
Map returnMap = new HashMap();
Iterator entries = properties.entrySet().iterator();
Map.Entry entry;
String name = "";
String value = null;
while (entries.hasNext()) {
entry = (Map.Entry) entries.next();
name = (String) entry.getKey();
Object valueObj = entry.getValue();
if(null == valueObj){
returnMap.put(name, value);
}else if(valueObj instanceof String[]){
String[] values = (String[])valueObj;
String[] resultValues = new String[values.length];
for(int i=0;i<values.length;i++){
resultValues[i] = stripXSS(values[i]);
}
returnMap.put(name, resultValues);
}else{
value = valueObj.toString();
returnMap.put(name, stripXSS(value));
}

}
return returnMap;
}

@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="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 </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("");
value = StringEscapeUtils.escapeHtml(value);
}
return value;
}
}

web.xml中配置

<filter>
<filter-name>XSSFilter</filter-name>
<filter-class>framework.filter.XSSFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>XSSFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>

需要注意的是如果项目使用了struts2则必须重写getParameterMap 才能生效。