Restricted Sessions for SSH

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.

Deprecation Warning

Restricted Sessions for SSH were deprecated in Teleport 14 and will be removed in Teleport 15.

Prerequisites

• A running Teleport cluster version 14.3.33 or above. If you want to get started with Teleport, sign up for a free trial or set up a demo environment.

• The tctl admin tool and tsh client tool.

  Visit Installation for instructions on downloading tctl and tsh.

• 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 name	Distro version	Kernel version
Ubuntu "Groovy Gorilla"	20.10	5.8+
Fedora	33	5.8+
Arch Linux	2020.09.01	5.8.5+
Flatcar	2765.2.2	5.10.25+

• To check that you can connect to your Teleport cluster, sign in with tsh login, then verify that you can run tctl commands using your current credentials. tctl is supported on macOS and Linux machines. For example:

  $ tsh login --proxy=teleport.example.com [email protected]
  $ tctl status
  # Cluster  teleport.example.com
  # Version  14.3.33
  # CA pin   sha256:abdc1245efgh5678abdc1245efgh5678abdc1245efgh5678abdc1245efgh5678
  If you can connect to the cluster and run the tctl status command, you can use your current credentials to run subsequent tctl commands from your workstation. If you host your own Teleport cluster, you can also run tctl commands on the computer that hosts the Teleport Auth Service for full permissions.

Network restrictions

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

• Firewall rules apply to the entire machine whereas network restrictions are applied only to SSH sessions.
• Whereas firewall typically blocks ingress (inbound) connections, network restrictions block egress (outbound) connections.
• 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.

warning

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
version: v3
teleport:
  nodename: graviton-node
  auth_token: exampletoken
  # Replace with the address of the Teleport Auth Server.
  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: v4
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

• See the Teleport Configuration Reference for more information on configuring Restricted Sessions.