From labs-no-reply@idefense.com Fri Apr 1 11:46:38 2005 From: iDEFENSE Labs To: bugtraq@securityfocus.com, vulnwatch@vulnwatch.org Date: Thu, 31 Mar 2005 18:23:04 -0500 Subject: iDEFENSE Security Advisory 03.31.05: PHP getimagesize() Multiple Denial of Service Vulnerabilities PHP getimagesize() Multiple Denial of Service Vulnerabilities iDEFENSE Security Advisory 03.31.05 www.idefense.com/application/poi/display?id=222&type=vulnerabilities March 31, 2005 I. BACKGROUND PHP is a widely-used general-purpose scripting language that is especially suited for Web development and can be embedded into HTML. More information is available at: http://www.php.net II. DESCRIPTION Remote exploitation of multiple denial of service vulnerabilities in the PHP Group's PHP scripting language allows attackers to consume CPU resources. The vulnerable routines, php_handle_iff() and php_handle_jpeg(), are reachable from the PHP function getimagesize(), which is defined as follows: array getimagesize ( string filename [, array &imageinfo] ) The getimagesize() routine is used to determine the size and dimensions of multiple image formats, including GIF, JPG, PNG, TIFF, etc. ISSUE 1 - php_handle_iff() Denial of Service Remote exploitation of a denial of service (DoS) condition in the PHP Group's PHP scripting language allows attackers to consume CPU resources. The problem specifically exists within the function php_handle_iff() defined in ext/standard/image.c. The vulnerability is demonstrated in the following excerpt: static struct gfxinfo *php_handle_iff(php_stream * stream TSRMLS_DC) { ... /* loop chunks to find BMHD chunk */ do { [1] if (php_stream_read(stream, a, 8) != 8) { efree(result); return NULL; } chunkId = php_ifd_get32s(a+0, 1); [2] size = php_ifd_get32s(a+4, 1); if ((size & 1) == 1) { size++; } if (chunkId == 0x424d4844) { /* BMHD chunk */ ... ... } else { [3] if (php_stream_seek(stream, size, SEEK_CUR)) { efree(result); return NULL; } } } while (1); } In the excerpt above, at line [1], 8 bytes are read from the user- supplied file stream. At line [2], the variables 'chunkId' and 'size' are set to user-supplied values from the file stream. If the variable 'size' is set to -8, then on line [3] the current position within the file stream is moved back 8 bytes, resulting in an infinite loop. ISSUE 2 - php_handle_jpeg() Denial of Service Local exploitation of an input validation vulnerability in The PHP Group's PHP embedded scripting language allows attackers to consume CPU resources. The vulnerability specifically exists due to insufficient validation of JPEG image file headers in the php_handle_jpeg() function. The JPEG file header contains a file length field which may be manipulated to cause an infinate loop in the copying of file data to memory as shown below from ext/standard/image.c: static struct gfxinfo * php_handle_jpeg (php_stream * stream, pval *info TSRMLS_DC) { struct gfxinfo *result = NULL; unsigned int marker = M_PSEUDO; unsigned short length, ff_read=1; for (;;) { [1] marker = php_next_marker(stream, marker, 1, ff_read TSRMLS_CC); ff_read = 0; switch (marker) { ... default: [2] php_skip_variable(stream TSRMLS_CC); break; } } return result; /* perhaps image broken -> no info but size */ } static void php_skip_variable(php_stream * stream TSRMLS_DC) { [3] off_t length = ((unsigned int)php_read2(stream TSRMLS_CC)); length = length-2; if (length) { [4] php_stream_seek(stream, (long)length, SEEK_CUR); } } The php_next_marker() call [1] reads the next byte in the stream to determine handling of the associated data. If given an invalid marker value, the case statement executes the default block which calls the php_skip_variable() function [2]. The php_read2() call [3] will return 0 bytes if the file stream has reached its end, so the pointer math causes a length value of -2 in the php_stream_seek() call[4]. This results in an infinate loop as the stream now points to the last two bytes of the file when the pointer is returned to the for loop in php_handle_jpeg(). III. ANALYSIS Exploitation of either vulnerability could allow unauthenticated remote attackers to consume 100% CPU resources on vulnerable systems. Exploitation requires that an attacker supply a malicious image to the getimagesize() PHP routine. The getimagesize() routine is frequently used when handling user-supplied image uploads, which increases the feasibility of remote exploitation. IV. DETECTION iDEFENSE has confirmed the existence of these vulnerabilities in PHP versions 4.2.2, 4.3.9, 4.3.10 and 5.0.3. V. WORKAROUND iDEFENSE is currently unaware of any workaround for this issue. VI. VENDOR RESPONSE These vulnerabilities are addressed in PHP 5.0.4 which is available for download at: www.php.net/distributions/php-5.0.4.tar.gz www.php.net/distributions/php-5.0.4.tar.bz2 VII. CVE INFORMATION The Common Vulnerabilities and Exposures (CVE) project has assigned the following names to these issues: CAN-2005-0524 - php_handle_iff() CAN-2005-0525 - php_handle_jpeg() These are candidates for inclusion in the CVE list (http://cve.mitre.org), which standardizes names for security problems. VIII. DISCLOSURE TIMELINE 02/23/2005 Initial vendor notification 02/23/2005 Initial vendor response 03/31/2005 Coordinated public disclosure IX. CREDIT The discoverer of these issues wishes to remain anonymous. Get paid for vulnerability research http://www.idefense.com/poi/teams/vcp.jsp Free tools, research and upcoming events http://labs.idefense.com X. LEGAL NOTICES Copyright (c) 2005 iDEFENSE, Inc. Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDEFENSE. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please email customerservice@idefense.com for permission. Disclaimer: The information in the advisory is believed to be accurate at the time of publishing based on currently available information. Use of the information constitutes acceptance for use in an AS IS condition. There are no warranties with regard to this information. Neither the author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information.