Metasploit-framework: Suggestion: add message to handle error when trying to use an invalid encoder

[cnotin]

Steps to reproduce

1. use exploit/windows/smb/psexec
2. set target 2 (native upload)
3. set other options as needed (login, password, rhost)
4. set SERVICE_STUB_ENCODER notfound

Here I make the mistake of selecting an invalid encoder (it happens, right? 😉)

Expected behavior

Metasploit should give me an explicit error "Invalid encoder 'notfound' selected"

Current behavior

We get a not very helpful error:

msf5 exploit(windows/smb/psexec) > run

[*] Started reverse TCP handler on 192.168.80.131:4444 
[*] a.b.c.d:445 - Connecting to the server...
[*] a.b.c.d:445 - Authenticating to a.b.c.d:445|cnn-lab as user 'clem'...
[!] a.b.c.d:445 - No active DB -- Credential data will not be saved!
[*] a.b.c.d:445 - Uploading payload... lvkZVaeg...exe
createx86/service
after create, encoder_mod=#<Msf::Modules::Encoder__X86__Service::MetasploitModule:0x00007fa39873c240>
datastore={}
before run
after run
createnotfound
after create, encoder_mod=
datastore={}
[-] a.b.c.d:445 - Exploit failed: NoMethodError undefined method `datastore' for nil:NilClass

As you can see I added some ugly prints (btw if you know a better way to work within MSF!) to debug the issue in lib/msf/core/payload_generator.rb:

    def multiple_encode_payload(shellcode)
      encoder_str = encoder[1..-1]
      encoder_str.scan(/([^:, ]+):?([^,]+)?/).map do |encoder_opt|
        @iterations = (encoder_opt[1] || 1).to_i
        @iterations = 1 if iterations < 1
        print("create"+encoder_opt[0]+"\n")
        encoder_mod = framework.encoders.create(encoder_opt[0])
        puts("after create, encoder_mod="+encoder_mod.to_s)
        puts("datastore="+datastore.to_s)
        encoder_mod.datastore.import_options_from_hash(datastore)
        puts("before run")
        shellcode = run_encoder(encoder_mod, shellcode)
        puts("after run")
      end
      shellcode
    end

It allows to see that when an encoder is invalid, encoder_mod = framework.encoders.create returns nil which triggers the exception below when calling encoder_mod.datastore

I'd like to offer a PR but I don't know this code enough to be confident :)

System stuff

Metasploit version

Latest version from Git

Actually I'm working on fixing this code and currently specifying an encoder won't do anything and you won't be able to reproduce it
Cf. #13407 and https://github.com/rapid7/metasploit-framework/issues/13407#issuecomment-625335717 from @jmartin-r7 explaining how the service encoder setting flows from psexec options to this code

[wvu-r7]

@cnotin: Check this out! https://github.com/pry/pry

[cnotin]

It looks very handy thanks @wvu-r7

[github-actions[bot]]

Hi!

This issue has been left open with no activity for a while now.

We get a lot of issues, so we currently close issues after 60 days of inactivity. It’s been at least 30 days since the last update here.
If we missed this issue or if you want to keep it open, please reply here. You can also add the label "not stale" to keep this issue open!

As a friendly reminder: the best way to see this issue, or any other, fixed is to open a Pull Request.

[cnotin]

I think it's still relevant

[github-actions[bot]]

Hi!

This issue has been left open with no activity for a while now.

We get a lot of issues, so we currently close issues after 60 days of inactivity. It’s been at least 30 days since the last update here.
If we missed this issue or if you want to keep it open, please reply here. You can also add the label "not stale" to keep this issue open!

As a friendly reminder: the best way to see this issue, or any other, fixed is to open a Pull Request.

[cnotin]

Please keep it up :)