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Restricted Sessions for SSH

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Restricted Session for SSH

Restricted Session for SSH

Length: 05:22

With a Restricted Session, Teleport allows the administrator to specify a policy to apply to SSH sessions. This policy can restrict access to certain resources. Currently Teleport supports network restrictions with more types coming in the future.

Prerequisites

  • A running Teleport cluster. For details on how to set this up, see one of our Getting Started guides.

  • The tctl admin tool and tsh client tool version >= 9.3.7.

    tctl version

    Teleport v9.3.7 go1.17

    tsh version

    Teleport v9.3.7 go1.17

    See Installation for details.

  • A running Teleport cluster. For details on how to set this up, see our Enterprise Getting Started guide.

  • The tctl admin tool and tsh client tool version >= 9.3.7, which you can download by visiting the customer portal.

    tctl version

    Teleport v9.3.7 go1.17

    tsh version

    Teleport v9.3.7 go1.17

  • A Teleport Cloud account. If you do not have one, visit the sign up page to begin your free trial.

  • The tctl admin tool and tsh client tool version >= 9.3.8. To download these tools, visit the Downloads page.

    tctl version

    Teleport v9.3.8 go1.17

    tsh version

    Teleport v9.3.8 go1.17

  • Linux kernel 5.8 (or above).

    You can check your kernel version using the uname command. The output should look something like the following.

    uname -r

    5.8.17

Linux distributions and supported kernels

Distro nameDistro versionKernel version
Ubuntu "Groovy Gorilla"20.105.8+
Fedora335.8+
Archlinux2020.09.015.8.5+
Flatcar2765.2.25.10.25+

To connect to Teleport, log in to your cluster using tsh, then use tctl remotely:

tsh login --proxy=teleport.example.com [email protected]
tctl status

Cluster teleport.example.com

Version 9.3.7

CA pin sha256:abdc1245efgh5678abdc1245efgh5678abdc1245efgh5678abdc1245efgh5678

You can run subsequent tctl commands in this guide on your local machine.

For full privileges, you can also run tctl commands on your Auth Service host.

To connect to Teleport, log in to your cluster using tsh, then use tctl remotely:

tsh login --proxy=myinstance.teleport.sh [email protected]
tctl status

Cluster myinstance.teleport.sh

Version 9.3.8

CA pin sha256:sha-hash-here

You must run subsequent tctl commands in this guide on your local machine.

Network Restrictions

Network restrictions work similarly to a firewall but with several differences:

  1. Firewall rules apply to the entire machine whereas network restrictions are applied only to SSH sessions.
  2. Whereas firewall typically blocks ingress (inbound) connections, network restrictions block egress (outbound) connections.
  3. Firewall rules are typically static but Teleport provides an API for Restricted Sessions that allows the rules to be dynamically updated across the entire fleet.

Step 1/4. Install and configure a Teleport Node

Set up your Teleport Node with the following content in /etc/teleport.yaml.

Restricted Sessions require Enhanced Recording to be enabled. This requirement will be removed in the future.

# Example config to be saved as /etc/teleport.yaml
teleport:
  nodename: graviton-node
  auth_token: exampletoken
  auth_servers:
  # Replace with the address of the Teleport Auth Server.
  - 127.0.0.1:3025
  data_dir: /var/lib/teleport
proxy_service:
  enabled: false
auth_service:
  enabled: false
ssh_service:
  enabled: true
  enhanced_recording:
    # Must be enabled for Restricted Sessions to work.
    enabled: true
    # Optional: Controls where cgroupv2 hierarchy is mounted. Default value:
    # /cgroup2.
    cgroup_path: /cgroup2

  restricted_session:
    enabled: true

Step 2/4. Define a network restrictions policy

Create a file called netpolicy.yaml:

kind: network_restrictions
version: v5
metadata:
  name: network-restrictions
spec:
  # When Restricted Sessions are enabled, the network policy becomes
  # "deny-all". Must add back the ranges to allow
  allow:
    # Allow LAN access
    - cidr: 10.0.0.0/8
    - cidr: 172.16.0.0/12
    - cidr: 192.168.0.0/16

    # Allow link-local
    - cidr: 169.254.0.0/16
    - cidr: fe80::/10

    # Allow localhost
    - cidr: 127.0.0.0/8
    - cidr: ::1/128

  # Override "allow" list with exceptions
  deny:
    # Finance database
    - cidr: 10.1.2.4

Install the policy using tctl:

tctl create -f netpolicy.yaml

network restrictions have been updated

If Restricted Sessions are not enabled in teleport.yaml, all network operations will be allowed. When Restricted Sessions are enabled but a network_restrictions object has not been created via tctl or the API, the default policy stays allow-all.

However when the network_restrictions object is created, the default policy switches to deny-all. If you expect network operations to target certain IP ranges, be sure to state these within the allow section.

Step 3/4. Test Restricted Sessions

curl -v https://google.com

* Trying 2607:f8b0:4005:809::200e:80...

* TCP_NODELAY set

* Immediate connect fail for 2607:f8b0:4005:809::200e: Operation not permitted

* Trying 172.217.6.78:80...

* TCP_NODELAY set

* Immediate connect fail for 172.217.6.78: Operation not permitted

* Closing connection 0

curl: (7) Couldn't connect to server

Step 4/4. Inspect logs

The Teleport audit log will contain an entry with a session.network event (there may be more entries present for the same curl command):

{
  "ei": 173,
  "event": "session.network",
  "uid": "dda39eb4-13e1-45fd-a039-35b4dca1fa51",
  "code": "T4002I",
  "time": "2021-07-22T22:24:14.984Z",
  "cluster_name": "teleport-quickstart",
  "user": "demo",
  "login": "demo",
  "sid": "c8e0b0d5-3994-4221-b701-c1ae17d871f1",
  "namespace": "default",
  "server_id": "4951c001-8dad-4e21-abb6-c03f69b72d2e",
  "pid": 319267,
  "cgroup_id": 10863,
  "program": "curl",
  "src_addr": "0.0.0.0",
  "dst_addr": "216.58.194.206",
  "dst_port": 80,
  "version": 4,
  "operation": 0,
  "action": 1
}

This is the same event that is issued by Enhanced Recording. You can differentiate them by the action field. Enhanced Recording sets the action to 0 (OBSERVED) while a Restricted Session sets this value to 1 (DENIED).

Tip

To quickly check the status of the audit log, you can simply tail the logs with tail -f /var/lib/teleport/log/events.log, the resulting capture from Teleport will be a JSON log for each command and network request.

Next steps