Amazon Web Services provides conveniently privileged backdoors in
the form of their SSM agents which do not require connectivity with
the target instance, merely valid credentials to AWS' API. Due to
this indirect "connection" paradigm, this mechanism can be used to
control otherwise "air-gapped" targets.
This approach abstracts asynchronous request/response parsing for
SSM requests into an IO channel with which the AWS SSM client is
then wrapped to emulate the expected Stream. The mechanism is rather
raw and could use better error handling, retries on laggy output,
and a threadsafe cursor implementation. It may be possible to start
an actually interactive session using the #start_session method in
the AWS client library, but so far testing has not yielded positive
results.
There is a significant limitation with these sessions not present
in normal stream-wise abstractions: a response limit of 2500 chars.
This limitation can be overcome by utilizing an S3 bucket to store
command output; however, due to the nature of access we seek to
obtain, it would not only add to the logged event loads but retain
the results of our TTPs in a "buffer" accessible to other people.
This functionality can be added down the line in the form of S3
config options in the handler to be passed into the SSM client for
command execution and acquisition of output.
Testing:
Gets sessions, provides command IO, leaves a bunch of log entries
in CloudTrail (something to keep in mind for opsec considerations).
Next steps:
Reorganize our WebSocket code a bit to provide connection and WS
state management inside Rex::Proto::Http::Client which can then be
exposed to the Handler without having to mix-in other namespaces
from Exploit.
Use the #start_session SSM Client method to extract the WS URL
for the relevant channel, and utilize that as the underpinning for
our session comms.
This reverts commit 6494603510, reversing
changes made to 5d3b8f8030.
By defining the missing constant early in startup we can force
reline to detect Fiddle as version '0.0.0' when the class is provide
by a Ruby 2.x implementation that has an documented version.
Grant Willcox