PHP 5.2.5 cURL safe_mode bypass
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[PHP 5.2.5 cURL safe_mode bypass ]
Author: Maksymilian Arciemowicz (cXIb8O3)
SecurityReason
Date:
- - Written: 21.08.2007
- - Public: 22.01.2008
SecurityReason Research
SecurityAlert Id: 51
CVE: CVE-2007-4850
SecurityRisk: Medium
Affected Software: PHP 5.2.4 and 5.2.5
Advisory URL:
http://securityreason.com/achievement_securityalert/51
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.
PHP supports libcurl, a library created by Daniel Stenberg, that allows you to
connect and communicate to many different types of servers with many different
types of protocols. libcurl currently supports the http, https, ftp, gopher,
telnet, dict, file, and ldap protocols. libcurl also supports HTTPS
certificates, HTTP POST, HTTP PUT, FTP uploading (this can also be done with
PHP's ftp extension), HTTP form based upload, proxies, cookies, and
user+password authentication.
These functions have been added in PHP 4.0.2.
- --- 1. cURL ---
This is very similar to CVE-2006-2563.
http://securityreason.com/achievement_securityalert/39
The first issue [SAFE_MODE bypass]
var_dump(curl_exec(curl_init("file://safe_mode_bypass\x00".__FILE__)));
is caused by error in curl/interface.c
- ---
#define PHP_CURL_CHECK_OPEN_BASEDIR(str, len, __ret)
\
if (((PG(open_basedir) && *PG(open_basedir)) || PG(safe_mode)) &&
\
strncasecmp(str, "file:", sizeof("file:") - 1) == 0)
\
{
\
php_url *tmp_url;
\
\
if (!(tmp_url = php_url_parse_ex(str, len))) {
\
php_error_docref(NULL TSRMLS_CC, E_WARNING, "Invalid
URL '%s'", str); \
php_curl_ret(__ret);
\
}
\
\
if (!php_memnstr(str, tmp_url->path, strlen(tmp_url->path), str
+ len)) { \
php_error_docref(NULL TSRMLS_CC, E_WARNING, "URL '%s'
contains unencoded control characters", str); \
php_url_free(tmp_url);
\
php_curl_ret(__ret);
\
}
\
\
if (tmp_url->query || tmp_url->fragment ||
php_check_open_basedir(tmp_url->path TSRMLS_CC) ||
\
(PG(safe_mode) && !php_checkuid(tmp_url->path, "rb+",
CHECKUID_CHECK_MODE_PARAM)) \
) {
\
php_url_free(tmp_url);
\
php_curl_ret(__ret);
\
}
\
php_url_free(tmp_url);
\
}
- ---
if you have tmp_url = php_url_parse_ex(str, len)
where:
str = "file://safe_mode_bypass\x00".__FILE__
and this function will return:
tmp_url->path = __FILE__
curl_init() functions checks safemode and openbasedir for tmp_url->path. Not
for real path.
- ---
if (argc > 0) {
char *urlcopy;
urlcopy = estrndup(Z_STRVAL_PP(url), Z_STRLEN_PP(url));
curl_easy_setopt(ch->cp, CURLOPT_URL, urlcopy);
zend_llist_add_element(&ch->to_free.str, &urlcopy);
}
- ---
the last step in curl_init() function will only copy file://safe_mode_bypass to
urlcopy.
The main problem exists in php_url_parse_ex() function. If you put in
curl_init() "file://host/somewhere/path.php", php_url_parse_ex() will select
/somewhere/path.php to path varible. Looks good but it cannot be used, when you
will check real path. Using file:///etc/passwd is correct but between file://
and /etc/passwd, php_url_parse_ex() will select host and return path to /passwd.
Tested in PHP 5.2.4 and PHP 5.2.5 (FreeBSD 6.2R)
cxib# php -v
PHP 5.2.5 with Suhosin-Patch 0.9.6.2 (cli) (built: Dec 10 2007 19:54:41) (DEBUG)
Copyright (c) 1997-2007 The PHP Group
Zend Engine v2.2.0, Copyright (c) 1998-2007 Zend Technologies
- --- 2. Exploit ---
SecurityReason will not public official exploit for this issue. But it is
possible to read file from another directories like /etc/passwd.
- --- 3. How to fix ---
CVS
http://cvs.php.net/viewcvs.cgi/php-src/NEWS?revision=1.2027.2.547.2.1047&view=markup
- ---
Fixed a safe_mode bypass in cURL identified by Maksymilian Arciemowicz.
- ---
- --- 4. Greets ---
sp3x, Infospec, p_e_a, schain, l5x and iliaa
- --- 5. Contact ---
Author: SecurityReason [ Maksymilian Arciemowicz ( cXIb8O3 ) ]
Email: cxib [at] securityreason [dot] com
GPG: http://securityreason.pl/key/Arciemowicz.Maksymilian.gpg [NEW KEY]
GPG: http://securityreason.pl/key/Arciemowicz.Maksymilian.gpg.old [OLD KEY]
http://securityreason.com
http://securityreason.pl
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