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{securityreason.com}PHP 5 *printf() - Integer Overflow

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[PHP 5.2.5 and prior : *printf() functions Integer Overflow ]

Author: Maksymilian Arciemowicz (cXIb8O3)
SecurityReason.com and SecurityReason.pl
- - Written: 01.03.2008
- - Public: 20.03.2008

SecurityReason Research
SecurityAlert Id: 52

SecurityRisk: Low

Affected Software: PHP 5.2.5 and prior
Advisory URL:
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@xxxxxxxxxxxxxxxxxxxxx:/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@xxxxxxxxxxxxxxxxxxxxx:/usr/obj/usr/src/sys/GENERIC  i386

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@xxxxxxxxxxxxx:/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 ---
SecurityReason will not public official exploit for this issue. 

- --- 3. How to fix ---


- --- 4. Greets ---
sp3x Infospec p_e_a Chujwamwdupe schain and Stanislav Malyshev (Patch)

- --- 5. Contact ---
Author: SecurityReason [ Maksymilian Arciemowicz ( cXIb8O3 ) ]
Email: cxib [at] securityreason [dot] com
GPG: http://securityreason.com/key/Arciemowicz.Maksymilian.gpg [NEW KEY]
GPG: http://securityreason.com/key/Arciemowicz.Maksymilian.gpg.old [OLD KEY]

Version: GnuPG v2.0.4 (FreeBSD)