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# 用JAVA Filter 修改XSS攻擊的漏洞
[參考網站](https://www.gushiciku.cn/pl/p54d/zh-tw)
首先需要引入JAR檔
```
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
<version>3.0-alpha-1</version>
<scope>provided</scope>
</dependency>
```
需要建立這些檔案
建立Filter
```java=\
package inspector.online.filter;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
public class XssFilter implements Filter {
@Override
public void destroy() {
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
// 使用包裝器
XSSRequestWrapper XSSRequestWrapper = new XSSRequestWrapper((HttpServletRequest) servletRequest);
filterChain.doFilter(XSSRequestWrapper, servletResponse);
}
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
}
```
建立Wrapper
```java=\
package inspector.online.filter;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import org.apache.commons.lang3.StringUtils;
public class XSSRequestWrapper extends HttpServletRequestWrapper {
public XSSRequestWrapper(HttpServletRequest request) {
super(request);
}
// 對陣列引數進行特殊字元過濾
@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] = clearXss(values[i]);
}
return encodedValues;
}
// 對引數中特殊字元進行過濾
@Override
public String getParameter(String name) {
String value = super.getParameter(name);
if (value == null) {
return null;
}
return clearXss(value);
}
// 覆蓋getParameterMap方法，將引數名和引數值都做xss & sql過濾 【一般post表單請求，或者前臺接收為實體需要這樣處理】
@SuppressWarnings({"rawtypes", "unchecked"})
@Override
public Map getParameterMap() {
Map<String, Object> paramMap = new HashMap<String, Object>();
Map<String, String[]> requestMap = super.getParameterMap();
Iterator<Entry<String, String[]>> it = requestMap.entrySet().iterator();
while (it.hasNext()) {
Entry<String, String[]> entry = it.next();
if (entry.getValue().length == 1) {
paramMap.put(xssEncode(entry.getKey()), xssEncode(entry.getValue()[0]));
} else {
String[] values = entry.getValue();
String value = "";
for (int i = 0; i < values.length; i++) {
value = values[i] + ",";
}
value = value.substring(0, value.length() - 1);
paramMap.put(xssEncode(entry.getKey()), xssEncode(entry.getValue()[0]));
}
}
return paramMap;
}
// 獲取attribute, 特殊字元過濾
@Override
public Object getAttribute(String name) {
Object value = super.getAttribute(name);
if (value != null && value instanceof String) {
clearXss((String) value);
}
return value;
}
// 對請求頭部進行特殊字元過濾
@Override
public String getHeader(String name) {
String value = super.getHeader(name);
if (value == null) {
return null;
}
return clearXss(value);
}
//特殊字元處理（轉義或刪除）
private String clearXss(String value) {
if (StringUtils.isEmpty(value)) {
return value;
}
// 字元編碼不一致，需要轉換。我們系統是UTF-8編碼，這裡不需要
/*
* try { value = new String(value.getBytes("ISO8859-1"), "UTF-8"); } catch (UnsupportedEncodingException e) { e.printStackTrace(); return null; }
*/
return XssFilterUtil.stripXss(value);
}
//將容易引起xss漏洞的半形字元直接替換成全形字元 在保證不刪除資料的情況下儲存
private static String xssEncode(String value) {
if (value == null || value.isEmpty()) {
return value;
}
value = value.replaceAll("eval\\((.*)\\)", "");
value = value.replaceAll("<", "<");
value = value.replaceAll(">", ">");
value = value.replaceAll("'", "'");
value = value.replaceAll("[\\\"\\\'][\\s]*javascript:(.*)[\\\"\\\']", "\"\"");
value = value.replaceAll("(?i)<script.*?>.*?<script.*?>", "");
value = value.replaceAll("(?i)<script.*?>.*?</script.*?>", "");
value = value.replaceAll("(?i)<.*?javascript:.*?>.*?</.*?>", "");
value = value.replaceAll("(?i)<.*?\\s+on.*?>.*?</.*?>", "");
// value = value.replaceAll("[<>{}\\[\\];\\&]","");
return value;
}
}
```
建立Util
```java=\
package inspector.online.filter;
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import org.apache.commons.lang3.StringUtils;
import org.apache.log4j.Logger;
public class XssFilterUtil {
private static final Logger log = Logger.getLogger(XssFilterUtil.class);
private static List<Pattern> patterns = null;
/**
* @Title: XSS常見攻擊
* @methodName: getXssPatternList
* @Description: Pattern.MULTILINE(? m)：在這種模式下，'^'和'$'分別匹配一行的開始和結束。此外，'^'仍然匹配字串的開始，'$'也匹配字串的結束。 預設情況下，這兩個表示式僅僅匹配字串的開始和結束。
* <p>
* Pattern.DOTALL(?s) ：在這種模式下，表示式'.'可以匹配任意字元，包括表示一行的結束符。 預設情況下，表示式'.'不匹配行的結束符。
*/
private static List<Object[]> getXssPatternList() {
List<Object[]> ret = new ArrayList<Object[]>();
ret.add(new Object[] {"<(no)?script[^>]*>.*?</(no)?script>", Pattern.CASE_INSENSITIVE});
ret.add(new Object[] {"</script>", Pattern.CASE_INSENSITIVE});
ret.add(new Object[] {"<script(.*?)>", Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL});
ret.add(new Object[] {"eval\\((.*?)\\)", Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL});
ret.add(new Object[] {"expression\\((.*?)\\)", Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL});
ret.add(new Object[] {"(javascript:|vbscript:|view-source:)*", Pattern.CASE_INSENSITIVE});
ret.add(new Object[] {"<(\"[^\"]*\"|\'[^\']*\'|[^\'\">])*>", Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL});
ret.add(new Object[] {"(window\\.location|window\\.|\\.location|document\\.cookie|document\\.|alert\\(.*?\\)|window\\.open\\()*",
Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL});
ret.add(new Object[] {
"<+\\s*\\w*\\s*(oncontrolselect|oncopy|oncut|ondataavailable|ondatasetchanged|ondatasetcomplete|ondblclick|ondeactivate|ondrag|ondragend|ondragenter|ondragleave|ondragover|ondragstart|ondrop|onerror=|onerroupdate|onfilterchange|onfinish|onfocus|onfocusin|onfocusout|onhelp|onkeydown|onkeypress|onkeyup|onlayoutcomplete|onload|onlosecapture|onmousedown|onmouseenter|onmouseleave|onmousemove|onmousout|onmouseover|onmouseup|onmousewheel|onmove|onmoveend|onmovestart|onabort|onactivate|onafterprint|onafterupdate|onbefore|onbeforeactivate|onbeforecopy|onbeforecut|onbeforedeactivate|onbeforeeditocus|onbeforepaste|onbeforeprint|onbeforeunload|onbeforeupdate|onblur|onbounce|oncellchange|onchange|onclick|oncontextmenu|onpaste|onpropertychange|onreadystatechange|onreset|onresize|onresizend|onresizestart|onrowenter|onrowexit|onrowsdelete|onrowsinserted|onscroll|onselect|onselectionchange|onselectstart|onstart|onstop|onsubmit|onunload)+\\s*=+",
Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.DOTALL});
return ret;
}
// XSS常見攻擊-正則表示式
private static List<Pattern> getPatterns() {
if (patterns == null) {
List<Pattern> list = new ArrayList<Pattern>();
String regex = null;
Integer flag = null;
int arrLength = 0;
for (Object[] arr : getXssPatternList()) {
arrLength = arr.length;
for (int i = 0; i < arrLength; i++) {
regex = (String) arr[0];
flag = (Integer) arr[1];
list.add(Pattern.compile(regex, flag));
}
}
patterns = list;
}
return patterns;
}
// 處理特殊字元
public static String stripXss(String value) {
if (StringUtils.isNotBlank(value)) {
log.info("【XSS攻擊防禦】，接收字元是：" + value);
Matcher matcher = null;
for (Pattern pattern : getPatterns()) {
matcher = pattern.matcher(value);
// 匹配
if (matcher.find()) {
// 刪除相關字串
value = matcher.replaceAll("");
}
}
log.info("【XSS攻擊防禦】，匹配正則是：" + matcher + "，處理後是：" + value);
/**
* 替換為轉移字元，類似HtmlUtils.htmlEscape
*/
// value = value.replaceAll("<", "<").replaceAll(">", ">");
// 刪除特殊符號
// String specialStr = "%20|=|!=|-|--|;|'|\"|%|#|+|//|/| |\\|<|>|(|)|{|}";
if (StringUtils.isNotBlank(value)) {
String specialStr = "%20|=|!=|-|--|;|'|\"|%|#|[+]|//|/| |\\|<|>|(|)|{|}";
for (String str : specialStr.split("\\|")) {
if (value.indexOf(str) > -1) {
value = value.replaceAll(str, "");
}
}
log.info("【XSS攻擊防禦】，特殊符號處理後是：" + value);
}
}
return value;
}
}
```
最後在web.xml加上過濾器
```xml
<!-- 解決xss漏洞 -->
<filter>
<filter-name>xssFilter</filter-name>
<filter-class>inspector.online.filter.XssFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>xssFilter</filter-name>
<!--過濾路徑 -->
<url-pattern>*</url-pattern>
</filter-mapping>
<!-- 解決xss漏洞 -->
```
---
如果要跟struts2整合在一起的話
web.xml要改成這樣
```xml
<!-- struts2 start -->
<filter>
<filter-name>struts2</filter-name>
<!-- <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class> -->
<filter-class>inspector.online.filter.XssFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<!-- struts2 end -->
```
把原本的struts2 filter 的class註解掉，改成自己的
然後把自己寫的XssFilter 去繼承StrutsPrepareAndExecuteFilter
```java=
package inspector.online.filter;
import java.io.IOException;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter;
public class XssFilter extends StrutsPrepareAndExecuteFilter {
/**
* 改寫 Filter 功能，使用新的 request 物件傳遞
*/
@Override
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
throws IOException, ServletException {
// 直接呼叫原有的方式，僅將 request 替換成 處理 xss 之 Request
System.out.println("XssFilter doFilter");
super.doFilter(new XSSRequestWrapper((HttpServletRequest) req), res, chain);
}
}
```
用postman去測試時，即可看到攻擊代碼被轉換掉了
###### tags: `XSS`
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