copy() Safe Mode Bypass PHP 4.4.2 and 5.1.2

2006.04.08
Risk: High
Local: Yes
Remote: No
CWE: N/A


CVSS Base Score: 2.1/10
Impact Subscore: 2.9/10
Exploitability Subscore: 3.9/10
Exploit range: Local
Attack complexity: Low
Authentication: No required
Confidentiality impact: Partial
Integrity impact: None
Availability impact: None

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 [copy() Safe Mode Bypass PHP 4.4.2 and 5.1.2] Author: Maksymilian Arciemowicz (cXIb8O3) Date: - -Written: 2.4.2006 - -Public: 8.4.2006 from SECURITYREASON.COM CVE-2006-1608 - --- 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 Sæther 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. The PHP safe mode is an attempt to solve the shared-server security problem. It is architecturally incorrect to try to solve this problem at the PHP level, but since the alternatives at the web server and OS levels aren't very realistic, many people, especially ISP's, use safe mode for now. - --- 1. Safe Mode Bypass --- General problem exists in safe mode function, because safe mode accept path like "compress.zlib://". PHP442 File "main/safe_mode.c" - -78-80--- wrapper = php_stream_locate_url_wrapper(filename, NULL, STREAM_LOCATE_WRAPPERS_ONLY TSRMLS_CC); if (wrapper != NULL) return 1; - -78-80--- if php_stream_locate_url_wrapper() return something.. safe mode is going to stop. Let`s see the function php_stream_locate_url_wrapper(). PHP442 File "main/streams.c" - -2522-2588--- PHPAPI php_stream_wrapper *php_stream_locate_url_wrapper(const char *path, char **path_for_open, int options TSRMLS_DC) { HashTable *wrapper_hash = (FG(stream_wrappers) ? FG(stream_wrappers) : &url_stream_wrappers_hash); php_stream_wrapper *wrapper = NULL; const char *p, *protocol = NULL; int n = 0; if (path_for_open) *path_for_open = (char*)path; if (options & IGNORE_URL) return (options & STREAM_LOCATE_WRAPPERS_ONLY) ? NULL : &php_plain_files_wrapper; for (p = path; isalnum((int)*p) || *p == '+' || *p == '-' || *p == '.'; p++) { n++; } if ((*p == ':') && (n > 1) && !strncmp("://", p, 3)) { protocol = path; } else if (strncasecmp(path, "zlib:", 5) == 0) { /* BC with older php scripts and zlib wrapper */ protocol = "compress.zlib"; n = 13; if (options & REPORT_ERRORS) { php_error_docref(NULL TSRMLS_CC, E_WARNING, "Use of \"zlib:\" wrapper is deprecated; please use \"compress.zlib://\" instead."); } } if (protocol) { if (FAILURE == zend_hash_find(wrapper_hash, (char*)protocol, n, (void**)&wrapper)) { char wrapper_name[32]; if (options & REPORT_ERRORS) { if (n >= sizeof(wrapper_name)) n = sizeof(wrapper_name) - 1; PHP_STRLCPY(wrapper_name, protocol, sizeof(wrapper_name), n); php_error_docref(NULL TSRMLS_CC, E_NOTICE, "Unable to find the wrapper \"%s\" - did you forget to enable it when you configured PHP?", wrapper_name); } wrapper = NULL; protocol = NULL; } } /* TODO: curl based streams probably support file:// properly */ if (!protocol || !strncasecmp(protocol, "file", n)) { if (protocol && path[n+1] == '/' && path[n+2] == '/') { if (options & REPORT_ERRORS) php_error_docref(NULL TSRMLS_CC, E_WARNING, "remote host file access not supported, %s", path); return NULL; } if (protocol && path_for_open) *path_for_open = (char*)path + n + 1; /* fall back on regular file access */ return (options & STREAM_LOCATE_WRAPPERS_ONLY) ? NULL : &php_plain_files_wrapper; } if (wrapper && wrapper->is_url && !PG(allow_url_fopen)) { if (options & REPORT_ERRORS) php_error_docref(NULL TSRMLS_CC, E_WARNING, "URL file-access is disabled in the server configuration"); return NULL; } return wrapper; } - -2522-2588--- So if you use in your path (for example "compress.zlib://"), function php_stream_locate_url_wrapper() return something variable and safe mode return 1. Let's see now the source of function copy(). PHP442: ext/standard/file.c - -2114-2138--- PHP_FUNCTION(copy) { zval **source, **target; if (ZEND_NUM_ARGS() != 2 || zend_get_parameters_ex(2, &source, &target) == FAILURE) { WRONG_PARAM_COUNT; } convert_to_string_ex(source); convert_to_string_ex(target); if (PG(safe_mode) &&(!php_checkuid(Z_STRVAL_PP(source), NULL, CHECKUID_CHECK_FILE_AND_DIR))) { RETURN_FALSE; } if (php_check_open_basedir(Z_STRVAL_PP(source) TSRMLS_CC)) { RETURN_FALSE; } if (php_copy_file(Z_STRVAL_PP(source), Z_STRVAL_PP(target) TSRMLS_CC)==SUCCESS) { RETURN_TRUE; } else { RETURN_FALSE; } } - -2114-2138--- http://pl2.php.net/manual/en/function.copy.php Description bool copy ( string source, string dest ) example: copy("compress.zlib:///etc/passwd", "/home/cxib/to/bandyta/passwd.txt"); safe mode return 1 and skip security. if (PG(safe_mode) &&(!php_checkuid(Z_STRVAL_PP(source), NULL, CHECKUID_CHECK_FILE_AND_DIR))) { RETURN_FALSE; } return true. Rest functions have checking safe_mode without path and safe mode works. I don't have tested all functions in php ;]. - --- 2. How to fix --- CVS http://cvs.php.net/viewcvs.cgi/php-src/NEWS - --- 3. Exploit --- http://securityreason.com/achievement_exploitalert/8 - --- 4. Greets --- For: sp3x and p_e_a, eax, Infospec - --- 5. Contact --- Author: SecurityReason.Com [ Maksymilian Arciemowicz ( cXIb8O3 ) ] Email: max [at] jestsuper [dot] pl or cxib [at] securityreason [dot] com GPG: http://securityreason.com/key/Arciemowicz.Maksymilian.gpg SecurityReason.Com -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2.2 (FreeBSD) iD8DBQFEOAu93Ke13X/fTO4RApXzAKC4OuM/3vn8kyw+EP2R8YVYyH9gkgCcDCMj 2dB55e2x6sPGBJW+w9Kw/OY= =Lfuk -----END PGP SIGNATURE-----


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