Bug #73032 [Asn->Ana]: mcrypt_create_iv write out-of-bounds

Edit report at https://bugs.php.net/bug.php?id=73032&edit=1 ID: 73032 Updated by: cmb@php.net Reported by: fernando at null-life dot com Summary: mcrypt_create_iv write out-of-bounds -Status: Assigned +Status: Analyzed Type: Bug Package: mcrypt related Operating System: Windows PHP Version: 7.0.10 -Assigned To: cmb +Assigned To: Block user comment: N Private report: N New Comment: I've submitted PR 2120. Previous Comments: ------------------------------------------------------------------------ [2016-09-07 13:08:26] fernando at null-life dot com Sorry, forgot to add that this test was done with USE_ZEND_ALLOC=0 ------------------------------------------------------------------------ [2016-09-07 12:20:05] cmb@php.net Did you run the test script with a custom memory manager (i.e. not with ZendMM)? ZendMM is supposed to bail out, if the memory can't be allocated (and did so in my tests), so line 1416 won't ever be reached. Therefore the NULL check for the ecalloc() on line 1373 is deliberately omitted, see bug #72828. ------------------------------------------------------------------------ [2016-09-06 15:57:15] fernando at null-life dot com Description: ------------ While generating IVs mcrypt extension fails to verify if the iv was allocated and then tries to write https://github.com/php/php-src/blob/master/ext/mcrypt/mcrypt.c#L1373 iv = ecalloc(size + 1, 1); if (source == RANDOM || source == URANDOM) { #if PHP_WIN32 /* random/urandom equivalent on Windows */ BYTE *iv_b = (BYTE *) iv; if (php_win32_get_random_bytes(iv_b, (size_t) size) == FAILURE){ efree(iv); php_error_docref(NULL, E_WARNING, "Could not gather sufficient random data"); RETURN_FALSE; } n = (int)size; #else ... #endif } else { n = (int)size; while (size) { ----> iv[--size] = (char) (255.0 * php_rand() / RAND_MAX); } Test script: --------------- <?php error_reporting(E_ALL); $v1=(0xffffffff / 4); mcrypt_create_iv($v1,0xFF); Expected result: ---------------- No crash Actual result: -------------- (347c.3ad4): Access violation - code c0000005 (first chance) First chance exceptions are reported before any exception handling. This exception may be expected and handled. php7!zif_mcrypt_create_iv+0x9a: 7787f8aa 880c07 mov byte ptr [edi+eax],cl ds:002b:3ffffffe=?? Processing initial command 'r;!exploitable -v' 0:000:x86> r;!exploitable -v eax=3ffffffe ebx=3fffffff ecx=000000f8 edx=00000000 esi=7787f810 edi=00000000 eip=7787f8aa esp=06f8e528 ebp=0a6200e0 iopl=0 nv up ei pl nz na po nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010202 php7!zif_mcrypt_create_iv+0x9a: 7787f8aa 880c07 mov byte ptr [edi+eax],cl ds:002b:3ffffffe=?? !exploitable 1.6.0.0 HostMachine\HostUser Executing Processor Architecture is x86 Debuggee is in User Mode Debuggee is a live user mode debugging session on the local machine Event Type: Exception *** ERROR: Symbol file could not be found. Defaulted to export symbols for C:\WINDOWS\SysWOW64\KERNEL32.DLL - *** ERROR: Symbol file could not be found. Defaulted to export symbols for ntdll.dll - Exception Faulting Address: 0x3ffffffe First Chance Exception Type: STATUS_ACCESS_VIOLATION (0xC0000005) Exception Sub-Type: Write Access Violation Faulting Instruction:7787f8aa mov byte ptr [edi+eax],cl Exception Hash (Major/Minor): 0x3a848ec3.0xd95bfbf6 Hash Usage : Stack Trace: Major+Minor : php7!zif_mcrypt_create_iv+0x9a Major+Minor : php7!execute_ex+0xfb Major+Minor : php7!zend_execute+0x124 Major+Minor : php7!zend_execute_scripts+0xe7 Major+Minor : php7!php_execute_script+0x372 Minor : php!do_cli+0x3d3 Minor : php!main+0x2cb Minor : php!__scrt_common_main_seh+0xf9 Minor : KERNEL32!BaseThreadInitThunk+0x24 Excluded : ntdll_77600000!RtlInitializeExceptionChain+0x8f Excluded : ntdll_77600000!RtlInitializeExceptionChain+0x5a Instruction Address: 0x000000007787f8aa Source File: c:\php-sdk\php70dev\vc14\x86\php-7.0.10\ext\mcrypt\mcrypt.c Source Line: 1416 Description: User Mode Write AV Short Description: WriteAV Exploitability Classification: EXPLOITABLE Recommended Bug Title: Exploitable - User Mode Write AV starting at php7!zif_mcrypt_create_iv+0x000000000000009a (Hash=0x3a848ec3.0xd95bfbf6) User mode write access violations that are not near NULL are exploitable. 0:000:x86> k ChildEBP RetAddr 06f8e534 777fdacb php7!zif_mcrypt_create_iv+0x9a [c:\php-sdk\php70dev\vc14\x86\php-7.0.10\ext\mcrypt\mcrypt.c @ 1416] 06f8e564 77816b64 php7!execute_ex+0xfb [c:\php-sdk\php70dev\vc14\x86\php-7.0.10\zend\zend_vm_execute.h @ 417] 06f8e590 778169c7 php7!zend_execute+0x124 [c:\php-sdk\php70dev\vc14\x86\php-7.0.10\zend\zend_vm_execute.h @ 459] 06f8e5e0 77816862 php7!zend_execute_scripts+0xe7 [c:\php-sdk\php70dev\vc14\x86\php-7.0.10\zend\zend.c @ 1427] 06f8f840 00f71833 php7!php_execute_script+0x372 [c:\php-sdk\php70dev\vc14\x86\php-7.0.10\main\main.c @ 2494] 06f8faf4 00f7135b php!do_cli+0x3d3 [c:\php-sdk\php70dev\vc14\x86\php-7.0.10\sapi\cli\php_cli.c @ 975] 06f8fb88 00f7229b php!main+0x2cb [c:\php-sdk\php70dev\vc14\x86\php-7.0.10\sapi\cli\php_cli.c @ 1344] 06f8fbd0 77177c04 php!__scrt_common_main_seh+0xf9 [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl @ 253] WARNING: Stack unwind information not available. Following frames may be wrong. 06f8fbe4 7765ab8f KERNEL32!BaseThreadInitThunk+0x24 06f8fc2c 7765ab5a ntdll_77600000!RtlInitializeExceptionChain+0x8f 06f8fc3c 00000000 ntdll_77600000!RtlInitializeExceptionChain+0x5a ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=73032&edit=1