PHP 5.2.0 session.save_path safe_mode and open_basedir bypass

2006.12.08
Risk: High
Local: Yes
Remote: No
CWE: N/A


CVSS Base Score: 4.6/10
Impact Subscore: 6.4/10
Exploitability Subscore: 3.9/10
Exploit range: Local
Attack complexity: Low
Authentication: No required
Confidentiality impact: Partial
Integrity impact: Partial
Availability impact: Partial

[PHP 5.2.0 session.save_path safe_mode and open_basedir bypass] Author: Maksymilian Arciemowicz Date: - - Written: 02.10.2006 - - Public: 08.12.2006 CVE: CVE-2006-6383 Risk: High Affected Software: PHP 5.2.0 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. A nice introduction to PHP by Stig Sather Bakken can be found at http://www.zend.com/zend/art/intro.php on the Zend website. Also, much of the PHP Conference Material is freely available. Session support in PHP consists of a way to preserve certain data across subsequent accesses. This enables you to build more customized applications and increase the appeal of your web site. A visitor accessing your web site is assigned a unique id, the so-called session id. This is either stored in a cookie on the user side or is propagated in the URL. session.save_path defines the argument which is passed to the save handler. If you choose the default files handler, this is the path where the files are created. Defaults to /tmp. See also session_save_path(). There is an optional N argument to this directive that determines the number of directory levels your session files will be spread around in. For example, setting to '5;/tmp' may end up creating a session file and location like /tmp/4/b/1/e/3/sess_4b1e384ad74619bd212e236e52a5a174If . In order to use N you must create all of these directories before use. A small shell script exists in ext/session to do this, it's called mod_files.sh. Also note that if N is used and greater than 0 then automatic garbage collection will not be performed, see a copy of php.ini for further information. Also, if you use N, be sure to surround session.save_path in "quotes" because the separator (;) is also used for comments in php.ini. - --- 1. session.save_path safe mode and open basedir bypass --- session.save_path can be set in ini_set(), session_save_path() function. In session.save_path there must be path where you will save yours tmp file. But syntax for session.save_path can be: [/PATH] OR [N;/PATH] N - can be a string. EXAMPLES: 1. session_save_path("/DIR/WHERE/YOU/HAVE/ACCESS") 2. session_save_path("5;/DIR/WHERE/YOU/HAVE/ACCESS") and 3. session_save_path("/DIR/WHERE/YOU/DONT/HAVE/ACCESS\0;/DIR/WHERE/YOU/HAVE/ACCESS") - -1477-1493--- Code from PHP520 ext/session/session.c [START] PHP_FUNCTION(session_save_path) { zval **p_name; int ac = ZEND_NUM_ARGS(); char *old; if (ac < 0 || ac > 1 || zend_get_parameters_ex(ac, &p_name) == FAILURE) WRONG_PARAM_COUNT; old = estrdup(PS(save_path)); if (ac == 1) { convert_to_string_ex(p_name); zend_alter_ini_entry("session.save_path", sizeof("session.save_path"), Z_STRVAL_PP(p_name), Z_STRLEN_PP(p_name), PHP_INI_USER, PHP_INI_STAGE_RUNTIME); } RETVAL_STRING(old, 0); } - -1477-1493--- Code from PHP520 ext/session/session.c [END] Values are set to hash_memory (but before that, safe_mode and open_basedir check this value). And if you are starting session (for example session_start()), that value from session.save_path is checked by function PS_OPEN_FUNC(files). - -242-300--- Code from PHP520 ext/session/mod_files.c [START] PS_OPEN_FUNC(files) { ps_files *data; const char *p, *last; const char *argv[3]; int argc = 0; size_t dirdepth = 0; int filemode = 0600; if (*save_path == '\0') { /* if save path is an empty string, determine the temporary dir */ save_path = php_get_temporary_directory(); } /* split up input parameter */ last = save_path; p = strchr(save_path, ';'); while (p) { argv[argc++] = last; last = ++p; p = strchr(p, ';'); if (argc > 1) break; } argv[argc++] = last; if (argc > 1) { errno = 0; dirdepth = (size_t) strtol(argv[0], NULL, 10); if (errno == ERANGE) { php_error(E_WARNING, "The first parameter in session.save_path is invalid"); return FAILURE; } } if (argc > 2) { errno = 0; filemode = strtol(argv[1], NULL, 8); if (errno == ERANGE || filemode < 0 || filemode > 07777) { php_error(E_WARNING, "The second parameter in session.save_path is invalid"); return FAILURE; } } save_path = argv[argc - 1]; data = emalloc(sizeof(*data)); memset(data, 0, sizeof(*data)); data->fd = -1; data->dirdepth = dirdepth; data->filemode = filemode; data->basedir_len = strlen(save_path); data->basedir = estrndup(save_path, data->basedir_len); PS_SET_MOD_DATA(data); return SUCCESS; } - -242-300--- Code from PHP520 ext/session/mod_files.c [END] Because in session.save_path there is a NULL byte before ";", strchr() doesn't see ";" and path is /DIR/WHERE/YOU/DONT/HAVE/ACCESS. Problem exists because safe_mode and open_basedir check what is after ;. And it is needed to set correct path after ";". - --- 2. How to fix --- http://cvs.php.net/viewcvs.cgi/php-src/NEWS - --- 3. Contact --- Author: Maksymilian Arciemowicz

References:

http://lists.suse.com/archive/suse-security-announce/2007-Mar/0003.html
http://cvs.php.net/viewcvs.cgi/php-src/ext/session/session.c?r1=1.336.2.53.2.7&r2=1.336.2.53.2.8
http://www.openpkg.com/security/advisories/OpenPKG-SA-2007.010.html
http://www.mandriva.com/security/advisories?name=MDKSA-2007:038


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