Generating `ysoserial` Java serialized objects

Instead of embedding static Java serialized objects, Metasploit offers ysoserial-generated binaries with built-in randomization. The benefits of using the Metasploit library include quicker module development, easier-to-read code, and future-proof Java serialized objects.

To use the ysoserial libraries, let's look at an example from the shiro_rememberme_v124_deserialize module:

Example code

In this example:

1. (L78) The module calls payload.encode to generate the command payload.
2. (L80) Then it sets the modified type to either bash or cmd based on the target.
3. (L81) Finally, the ysoserial library is used to generate a CommonsCollections2-based serialized object.

78    cmd = payload.encoded
79    vprint_status("Execute CMD: #{cmd}")
80    type = (target.name == 'Unix Command payload' ? 'bash' : 'cmd')
81    java_payload = ::Msf::Util::JavaDeserialization.ysoserial_payload('CommonsCollections2', cmd, modified_type: type)

Once the serialized object is generated and stored as java_payload, it's then sent to the target in an exploit-specific manner.

Calling ysoserial_payload

#ysoserial_payload(payload_name, command=nil, modified_type: 'original')

• payload_name - The payload name parameter must be one of the supported payloads stored in the ysoserial cache. As of this writing, the list includes: BeanShelll1, Clogure, CommonBeanutils1, CommonsCollections2, CommonsCollections3, CommonsCollections4, CommonsCollections5, CommonsCollections6, Groovy1, Hibernate1, JBossInterceptors1, JRMPClient, JSON1, JavassistWeld1, Jdk7u21, MozillaRhino1, Myfaces1, ROME, Spring1, Spring2, and Vaadin1. While ysoserial includes additional payloads that are not listed above, they are unsupported by the library due to the need for complex inputs. Should there be use cases for additional payloads, please consider opening an issue and submitting a pull request to add support.

• command - The command parameter will be executed by the remote system. The parameter is OS-agnostic, meaning that the module must determine the OS and architecture, if necessary, before generating a payload.

• modified_type - Use a modified version that invokes the specified shell (except in the case of original). For more information regarding the invocation, see CmdExecuteHelper.java. The value must be one of the following:

  • bash - A modified version that will invoke the command using the bash executable
  • cmd - A modified version that will invoke the command using the Windows cmd.exe executable.
  • original - The original ysoserial invocation without an OS-specific shell. Be careful when using this option as some ysoserial payloads (as specified using the payload_name parameter are incompatible with commands that contain the " character. For this reason, it is recommended that an OS-specific version be used when available. Some ysoserial payloads pass the OS command to execute to Runtime.getRuntime().exec as a string instead of an array of strings, leading to execution errors.
  • powershell - A modified version that will invoke the command using the Windows powershell.exe executable.

Regenerating the ysoserial_payload JSON file (MAINTAINERS ONLY)

Neither module developers nor users need to concern themselves with the following.

Click to expand

On occasion, Metasploit maintainers may want to re-run the script generation to incorporate new Java serialized objects from the ysoserial tool.

To avoid invoking Java (and all its dependencies) at runtime, the serialized objects are generated and cached within a JSON file. The JSON file can be refreshed using a standalone Ruby script, which comes prepackaged with a Docker image that handles downloading ysoserial and necessary dependencies. The script, Dockerimage and a high-level runme.sh script is stored within tools/payloads/ysoserial. An example run looks like:

$ cd ~/git/r7/metasploit-framework/tools/payloads/ysoserial
$ ./runme.sh 
Sending build context to Docker daemon  101.8MB
Step 1/8 : FROM ubuntu
 ---> cd6d8154f1e1
Step 2/8 : RUN apt update && apt -y upgrade
 ---> Using cache
 ---> ba7e5691ed5a
Step 3/8 : RUN apt install -y wget openjdk-8-jre-headless ruby-dev make gcc
 ---> Using cache
 ---> d38488663627
Step 4/8 : RUN wget -q https://jitpack.io/com/github/frohoff/ysoserial/master-SNAPSHOT/ysoserial-master-SNAPSHOT.jar -O ysoserial-original.jar
 ---> Using cache
 ---> 284ff722464b
Step 5/8 : RUN wget -q https://github.com/pimps/ysoserial-modified/raw/master/target/ysoserial-modified.jar
 ---> Using cache
 ---> 334c1ccb6fab
Step 6/8 : RUN gem install --silent diff-lcs json pry
 ---> Using cache
 ---> 9d452be9d01f
Step 7/8 : COPY find_ysoserial_offsets.rb /
 ---> 61b6f339590c
Step 8/8 : CMD ruby /find_ysoserial_offsets.rb
 ---> Running in ba7b14646e56
Removing intermediate container ba7b14646e56
 ---> f4ca5ecb6848
Successfully built f4ca5ecb6848
Successfully tagged ysoserial-payloads:latest
Generating payloads for BeanShell1...
Generating payloads for C3P0...
    Error while generating or serializing payload
    java.lang.IllegalArgumentException: Command format is: <base_url>:<classname>
    	at ysoserial.payloads.C3P0.getObject(C3P0.java:48)
    	at ysoserial.GeneratePayload.main(GeneratePayload.java:34)
  ERROR: Errored while generating 'C3P0' and it will not be supported
Generating payloads for Clojure...
Generating payloads for CommonsBeanutils1...
Generating payloads for CommonsCollections1...
Generating payloads for CommonsCollections2...
Generating payloads for CommonsCollections3...
Generating payloads for CommonsCollections4...
Generating payloads for CommonsCollections5...
Generating payloads for CommonsCollections6...
Generating payloads for FileUpload1...
    Error while generating or serializing payload
    java.lang.IllegalArgumentException: Unsupported command  []
    	at ysoserial.payloads.FileUpload1.getObject(FileUpload1.java:71)
    	at ysoserial.payloads.FileUpload1.getObject(FileUpload1.java:40)
    	at ysoserial.GeneratePayload.main(GeneratePayload.java:34)
  ERROR: Errored while generating 'FileUpload1' and it will not be supported
Generating payloads for Groovy1...
Generating payloads for Hibernate1...
Generating payloads for Hibernate2...
    Error while generating or serializing payload
    java.sql.SQLException: DataSource name cannot be empty string
    	at javax.sql.rowset.BaseRowSet.setDataSourceName(BaseRowSet.java:855)
    	at com.sun.rowset.JdbcRowSetImpl.setDataSourceName(JdbcRowSetImpl.java:4307)
    	at ysoserial.payloads.Hibernate2.getObject(Hibernate2.java:58)
    	at ysoserial.GeneratePayload.main(GeneratePayload.java:34)
  ERROR: Errored while generating 'Hibernate2' and it will not be supported
Generating payloads for JBossInterceptors1...
Generating payloads for JRMPClient...
Generating payloads for JRMPListener...
    Error while generating or serializing payload
    java.lang.NumberFormatException: For input string: ""
    	at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    	at java.lang.Integer.parseInt(Integer.java:592)
    	at java.lang.Integer.parseInt(Integer.java:615)
    	at ysoserial.payloads.JRMPListener.getObject(JRMPListener.java:42)
    	at ysoserial.payloads.JRMPListener.getObject(JRMPListener.java:34)
    	at ysoserial.GeneratePayload.main(GeneratePayload.java:34)
  ERROR: Errored while generating 'JRMPListener' and it will not be supported
Generating payloads for JSON1...
Generating payloads for JavassistWeld1...
Generating payloads for Jdk7u21...
Generating payloads for Jython1...
    Error while generating or serializing payload
    java.lang.IllegalArgumentException: Unsupported command  []
    	at ysoserial.payloads.Jython1.getObject(Jython1.java:52)
    	at ysoserial.payloads.Jython1.getObject(Jython1.java:42)
    	at ysoserial.GeneratePayload.main(GeneratePayload.java:34)
  ERROR: Errored while generating 'Jython1' and it will not be supported
Generating payloads for MozillaRhino1...
Generating payloads for Myfaces1...
Generating payloads for Myfaces2...
    Error while generating or serializing payload
    java.lang.IllegalArgumentException: Command format is: <base_url>:<classname>
    	at ysoserial.payloads.Myfaces2.getObject(Myfaces2.java:47)
    	at ysoserial.GeneratePayload.main(GeneratePayload.java:34)
  ERROR: Errored while generating 'Myfaces2' and it will not be supported
Generating payloads for ROME...
Generating payloads for Spring1...
Generating payloads for Spring2...
Generating payloads for URLDNS...
    Error while generating or serializing payload
    java.net.MalformedURLException: no protocol: 
    	at java.net.URL.<init>(URL.java:593)
    	at ysoserial.payloads.URLDNS.getObject(URLDNS.java:56)
    	at ysoserial.GeneratePayload.main(GeneratePayload.java:34)
  ERROR: Errored while generating 'URLDNS' and it will not be supported
Generating payloads for Vaadin1...
Generating payloads for Wicket1...
    Error while generating or serializing payload
    java.lang.IllegalArgumentException: Bad command format.
    	at ysoserial.payloads.Wicket1.getObject(Wicket1.java:59)
    	at ysoserial.payloads.Wicket1.getObject(Wicket1.java:49)
    	at ysoserial.GeneratePayload.main(GeneratePayload.java:34)
  ERROR: Errored while generating 'Wicket1' and it will not be supported
DONE!  Successfully generated 0 static payloads and 22 dynamic payloads.  Skipped 8 unsupported payloads.

At completion, the data/ysoserial_payloads.json file is overwritten and the 22 dynamic payloads are ready for use within the framework. Afterward, the developer should follow the standard git procedures to add and commit the new JSON file before generating a pull request and landing the updated JSON into the framework's master branch.