Not able to find a proper encoder with Fetch Payloads

[cdelafuente-r7]

This issue came out while working on this PR. This comment gives more details.

When some BadChars are set, Framework tries to find a suitable encoder according to the platform and the architecture. With a fetch payload, it fails:

[-] Exploit failed: cmd/linux/http/x64/meterpreter/reverse_tcp: All encoders failed to encode.

When setting the payload to a standard command payload (e.g. cmd/unix/reverse_bash), it works.

I found out the payload platforms are all set to linux platforms:

From: /Users/cdelafuente/dev/src/metasploit-framework/lib/msf/core/encoded_payload.rb:567 Msf::EncodedPayload#compatible_encoders:

    562: def compatible_encoders
    563:   arch = reqs['Arch'] || pinst.arch
    564:   platform = reqs['Platform'] || pinst.platform
    565:   require 'pry';binding.pry
    566:
 => 567:   encoders = []
    568:
    569:   framework.encoders.each_module_ranked(
    570:     'Arch' => arch, 'Platform' => platform) { |name, mod|
    571:     encoders << [ name, mod ]
    572:   }
    573:
    574:   encoders
    575: end

[1] pry(#<Msf::EncodedPayload>)> pinst.platform
=> #<Msf::Module::PlatformList:0x00007fbf69abf1f0 @platforms=[Msf::Module::Platform::Linux, Msf::Module::Platform::Linux]>
[2] pry(#<Msf::EncodedPayload>)> pinst.arch
=> ["cmd"]

So, no encoder is found with both a cmd architecture and a linux platform:

[1] pry(#<Msf::EncodedPayload>)> encoders
=> [["generic/none", Msf::Modules::Encoder__Generic__None::MetasploitModule], ["generic/eicar", Msf::Modules::Encoder__Generic__Eicar::MetasploitModule]]

While with a command payload, the unix platform is correctly set:

[1] pry(#<Msf::EncodedPayload>)> pinst.platform
=> #<Msf::Module::PlatformList:0x00007fbf68dd6ce0 @platforms=[Msf::Module::Platform::Unix]>

Steps to reproduce

1. Use an exploit that supports Fetch Payloads (e.g. linux/http/vinchin_backup_recovery_cmd_inject)
2. Make sure some BadChars are specified in the info hash (e.g. 'Payload' => { 'BadChars' => "\"'<>&" })
3. Do: set payload cmd/linux/http/x64/meterpreter/reverse_tcp
4. set the required options
5. Do: exploit

Try again with a command payload cmd/unix/reverse_bash. It should work now.

Expected behavior

The exploit should execute without encoding errors.

Current behavior

It fails with this error:

[-] Exploit failed: cmd/linux/http/x64/meterpreter/reverse_tcp: All encoders failed to encode.

[smcintyre-r7]

Easiest way to fix this might be to check if you can add linux as a platform to the existing encoders where unix is already listed.

[github-actions]

Hi!

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