pypsexec 0.0.1.dev2

Features

With pypsexec you can run commands of a remote Windows host like you would with psexec. This tools can configuration this process with the following features;

• Run as a specific local or domain user or the user

• Run as the local SYSTEM account

• Run as an interactive process

• Specify the session the interactive process should run on

• Specify the run level, highest or limited

• Set the priority of the process

• Set a timeout for the remote process

• Send input through the stdin pipe to the running process

• Set the processors the process can run on

Further Info

These are the steps the library completes to work;

• Create an SMB connection to the host

• Copies across the PAExec binary to the ADMIN$ share of the remote host

• Binds the Windows Service Manager to the opened IPC$ tree using RPC

• Creates and starts a Windows service as the SYSTEM accound to run the bianry copied

• Connect to the PAExec named pipe the service runs

• Sends the process details to the PAExec service through the pipe

• Send a request to the PAExec service to start the process based on the settings sent

• Connect to the newly spawned process’s stdout, stderr, stdin pipe (if not interactive or async)

• Read the stdout/stderr pipe until the process is complete

• Get the return code of the new process

• Stop and remove the PAExec service

• Remove the PAExec binary from the ADMIN$ share

In the case of a failed process, the PAExec service and binary may not be removed from the host and may need to be done manually. This is only the case for a critical error or the cleanup functions not being called.

By default the data being sent to and from the server is encrypted to stop people listening in on the network from snooping your data but this is only supported for Server 2012 or Windows 8 onwards. Older hosts like Windows 7 or Server 2008 R2 will still work but without encryption. There is nothing that can be done about thi as the encryption is based on the underlying SMB transport and these older hosts don’t support SMB encryption.

To disable encryption, set encrypt=False when initialising the Client class. Unfortunately PAExec does not encrypt the data sent across the network so command lines, credentials would be sent in plain text if SMB encryption is not used. While the data is not encrypted, it does a simple XOR scramble of the settings data but it is not as good as SMB encryption.

Requirements

• Python 2.7, 2.7, 3.4-3.6

• smbprotocol

To install pypsexec, simply run

pip install pypsexec

This will download the required packages that are required and get your Python environment ready to do.

Out of the box, pypsexec supports authenticating to a Windows host with NTLM authentication but users in a domain environment can take advantage of Kerberos authentication as well for added security. Currently the Windows implementation of the smbprotocol does not support Kerberos auth but for other platforms you can add support by running

# for Debian/Ubuntu/etc:
sudo apt-get install gcc python-dev libkrb5-dev
pip install smbprotocol[kerberos]

# for RHEL/CentOS/etc:
sudo yum install gcc python-devel krb5-devel krb5-workstation python-devel
pip install smbprotocol[kerberos]

From there to check that everything was installed correctly and the correct GSSAPI extensions are available on that host, run

try:
    from gssapi.raw import inquire_sec_context_by_oid
    print("python-gssapi extension is available")
except ImportError as exc:
    print("python-gssapi extension is not available: %s" % str(exc))

If it isn’t available, then either a newer version of the system’s gssapi implementation needs to be setup and python-gssapi compiled against that newer version.

Remote Host Requirements

The goal of this package to be able to run executables on a vanilla remote Windows host without any customisations. Saying that, some of the protocols used can be modified or disabled and would stop the package from working. What pypsexec requires is;

• SMB to be up and running on the Windows port and readable from the Python host

• The ADMIN$ share to be enabled with read/write access of the user configured

• The above usually means the configured user is an administrator of the Windows host

• At least SMB 2 on the host (Server 2008 and newer)

Examples

Here is an example of how to run a command with this library

from pypsexec.client import Client

# creates an encrypted connection to the host with the username and password
c = Client("server", username="username", password="password")

# set encrypt=False for Windows 7, Server 2008
c = Client("server", username="username", password="password")

# if Kerberos is available, this will use the default credentials in the
# credential cache
c = Client("server")

# you can also tell it to use a specific Kerberos principal in the cache
# without a password
c = Client("server", username="username@DOMAIN.LOCAL")

c.connect()
try:
    c.create_service()

    # After creating the service, you can run multiple exe's without
    # reconnecting

    # run a simple cmd.exe program with arguments
    stdout, stderr, rc = c.run_executable("cmd.exe",
                                          arguments="/c echo Hello World")

    # run whoami.exe as the SYSTEM account
    stdout, stderr, rc = c.run_executable("whoami.exe", use_system_account=True)

    # run command asynchronously (in background), the rc is the PID of the spawned service
    stdout, stderr, rc = c.run_executable("longrunning.exe",
                                          arguments="/s other args",
                                          async=True)

    # run whoami.exe as a specific user
    stdout, stderr, rc = c.run_executable("whoami",
                                          arguments="/all",
                                          username="local-user",
                                          password="password",
                                          run_elevated=True)
finally:
    c.remove_service()
    c.disconnect()

In the case of a fatal failure, this project may leave behind some the PAExec payload in C:\Windows or the service still installed. As these are uniquely named they can build up over time. They can be manually removed but you can also use pypsexec to cleanup them all up at once. To do this run

from pypsexec.client import Client

c = Client("server", username="username", password="password")
c.connect()
c.cleanup()  # this is where the magic happens
c.disconnect()

The script will delete any files that match C:\Windows\PAExec-* and any services that match PAExec-*. For an individual run, the remove_service() function should still be used.

Logging

This library uses the builtin Python logging library and can be used to find out what is happening in the pypsexec process. Log messages are logged to the pypsexec named logger as well as pypsexec.* where * is each python script in the pypsexec directory.

These logs are generally useful when debugging issues as they give you a more step by step snapshot of what it is doing and what may be going wrong. The debug level will also print out a human readable string of each SMB packet that is sent out from the client but this level can get really verbose.

Testing

To this module, you need to install some pre-requisites first. This can be done by running;

pip install -r requirements-test.txt

# you can also run tox by installing tox
pip install tox

From there to run the basic tests run;

py.test -v --pep8 --cov pypsexec --cov-report term-missing

# or with tox 2.7, 2.7, 3.4, 3.5, and 3.6
tox

There are extra tests that only run when certain environment variables are set. To run these tests set the following variables;

• PYPSEXEC_SERVER: The hostname or IP to a Windows host

• PYPSEXEC_USERNAME: The username to use authenticate with

• PYPSEXEC_PASSWORD: The password for PYPSEXEC_USERNAME

From there, you can just run tox or py.test with these environment variables to run the integration tests.