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.

Prerequisites

• 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

tsh login --proxy=teleport.example.com [email protected]
tctl status
Cluster  teleport.example.com
Version  12.1.1
CA pin   sha256:abdc1245efgh5678abdc1245efgh5678abdc1245efgh5678abdc1245efgh5678

tsh login --proxy=myinstance.teleport.sh [email protected]
tctl status
Cluster  myinstance.teleport.sh
Version  12.1.1
CA pin   sha256:sha-hash-here

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.

# 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).

Next steps

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