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Enhanced SSH Session Recording with BPF
Enhanced SSH Session Recording with BPF

Length: 05:01

Version: 14.x

Enhanced Session Recording for SSH with BPF

This guide explains Enhanced Session Recording for SSH with BPF and how to set it up in your Teleport cluster.

Teleport's default SSH and Kubernetes session recording feature captures what is echoed to a terminal.

This has inherent advantages. For example, because no input is captured, Teleport session recordings typically do not contain passwords that were entered into a terminal.

The disadvantage is that there are several techniques for rendering session recordings less useful:

  • Obfuscation. For example, even though the command echo Y3VybCBodHRwOi8vd3d3LmV4YW1wbGUuY29tCg== | base64 --decode | sh does not contain curl http://www.example.com, when decoded, that is what is run.
  • Shell scripts. For example, if a user uploads and executes a script, the commands run within the script are not captured, only the output.
  • Terminal controls. Terminals support a wide variety of controls including the ability for users to disable terminal echo. This is frequently used when requesting credentials. Disabling terminal echo allows commands to be run without being captured.

Furthermore, due to their unstructured nature, session recordings are difficult to ingest and perform monitoring and alerting on.

Teleport Enhanced Session Recording mitigates all three concerns by providing advanced security and greater logging capabilities, and better correlates a user with their activities.

Security Warning

Teleport Enhanced Session Recording does not provide a secure environment on its own and is not a substitute for a Linux Security Module (SELinux, AppArmor, etc.). It must be paired with reasonable system hardening practices to enforce a trusted host environment, including proper access control on core system binaries and libraries and well-designed user management.

Note that privileged users (either as root or via sudo) can interfere with session recording activities (such as unloading/disabling the necessary libraries, altering how Teleport is run, tampering with kernel functionality, creating tunnels, or just performing actions outside of the restricted session). Also, a local user with both monitored and unmonitored console sessions or ptrace privileges may not be fully captured in recordings.

Commands executed via daemons (systemd, crond, atd, etc.) could be outside of the recorded session scope. Proper network-based restrictions for ingress traffic must also be implemented to prevent possible unauthorized data transfer.

Additionally, certain forensic information such as full binary paths (accounting for any potential symbolic links), any modifications via shared library preloading, and environment variables may not be captured in session recordings.

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.

  • At least one host that you will use to run the Teleport Node Service. The host must run 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

    See below for more details on the required versions for your Linux kernel and distribution.

tip

Our Standard Session Recording works with older Linux kernels. View Teleport Session Recording for more details.

Linux distributions and supported kernels​

Teleport supports enhanced session recording with BPF on amd64 and arm64 architectures.

Distro nameDistro versionKernel Version
Ubuntu "Groovy Gorilla"20.105.8+
Fedora335.8+
Arch Linux2020.09.015.8.5+
Flatcar2765.2.25.10.25+
Amazon Linux2 and 20235.10+
  • 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.

Step 1/2. Configure a Teleport Node​

Install Teleport on your Node​

On the host where you will run your Teleport Node, follow the instructions for your environment to install Teleport.

Select an edition, then follow the instructions for that edition to install Teleport.

The following command updates the repository for the package manager on the local operating system and installs the provided Teleport version:

$ curl https://cdn.teleport.dev/install-v14.3.33.sh | bash -s 14.3.33

Generate a token​

Use the tctl tool to generate an invite token that your Node will use to join the cluster. In the following example, a new token is created with a TTL of five minutes:

# Generate a short-lived invitation token for a new node:
$ tctl nodes add --ttl=5m --roles=node
# The invite token: abcd123-insecure-do-not-use-this

# You can also list all generated non-expired tokens:
$ tctl tokens ls
# Token                            Type            Expiry Time
# ------------------------         -----------     ---------------
# abcd123-insecure-do-not-use-this         Node            25 Sep 18 00:21 UTC

# ... or revoke an invitation token before it's used:
$ tctl tokens rm abcd123-insecure-do-not-use-this

Create a configuration file​

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
  # The token you created earlier
  auth_token: abcd123-insecure-do-not-use-this

  # Replace with the address of the Teleport Auth Service
  auth_server: 127.0.0.1:3025
  # Or specify the Proxy Service address.
  proxy_server: 127.0.0.1:3080

  data_dir: /var/lib/teleport
proxy_service:
  enabled: false
auth_service:
  enabled: false
ssh_service:
  enabled: true
  enhanced_recording:
    # Enable or disable enhanced auditing for this node. Default value: false.
    enabled: true

    # Optional: command_buffer_size is optional with a default value of 8 pages.
    command_buffer_size: 8

    # Optional: disk_buffer_size is optional with default value of 128 pages.
    disk_buffer_size: 128

    # Optional: network_buffer_size is optional with default value of 8 pages.
    network_buffer_size: 8

    # Optional: Controls where cgroupv2 hierarchy is mounted. Default value:
    # /cgroup2.
    cgroup_path: /cgroup2

    # Optional: Controls the path inside cgroupv2 hierarchy where Teleport
    # cgroups will be placed. Default value: /teleport
    root_path: /teleport
Isolate session system resources

If you operate multiple Teleport instances on the same system, customize the root_path configuration to change the base cgroupv2 slice path for session system resources. This ensures security isolation between sessions from different Teleport instances, allowing you to apply distinct security rules and resource controls.

Start Teleport on your Node​

Configure the Teleport SSH Service to start automatically when the host boots up by creating a systemd service for it. The instructions depend on how you installed the Teleport SSH Service.

On the host where you will run the Teleport SSH Service, enable and start Teleport:

$ sudo systemctl enable teleport
$ sudo systemctl start teleport

You can check the status of the Teleport SSH Service with systemctl status teleport and view its logs with journalctl -fu teleport.

Step 2/2. Inspect the audit log​

Enhanced session recording events will be shown in Teleport's audit log, which you can inspect by visiting Teleport's Web UI.

Each command run will generate a session.command event, similar to the following:

{
  "argv": [
    "https://wttr.in"
  ],
  "cgroup_id": 2360,
  "cluster_name": "purple",
  "code": "T4000I",
  "ei": 50,
  "event": "session.command",
  "login": "ec2-user",
  "namespace": "default",
  "path": "/bin/curl",
  "pid": 5007,
  "ppid": 4985,
  "program": "curl",
  "return_code": 0,
  "server_hostname": "ip-172-31-34-128.us-east-2.compute.internal",
  "server_id": "531dc1de-c2c9-49bd-a0e3-4f4f3a523f5f",
  "sid": "86aca627-971d-4883-854d-d309ba04c658",
  "time": "2023-07-04T16:42:20.54Z",
  "uid": "9b825e22-744d-4130-94c5-dea49198ae3d",
  "user": "[email protected]"
}

Network connections will be logged as session.network events, similar to the following:

{
  "action": 0,
  "cgroup_id": 2360,
  "cluster_name": "purple",
  "code": "T4002I",
  "dst_addr": "5.9.243.187",
  "dst_port": 443,
  "ei": 51,
  "event": "session.network",
  "login": "ec2-user",
  "namespace": "default",
  "operation": 0,
  "pid": 5007,
  "program": "curl",
  "server_hostname": "ip-172-31-34-128.us-east-2.compute.internal",
  "server_id": "531dc1de-c2c9-49bd-a0e3-4f4f3a523f5f",
  "sid": "86aca627-971d-4883-854d-d309ba04c658",
  "src_addr": "172.31.34.128",
  "time": "2023-07-04T16:42:20.55Z",
  "uid": "da151350-bf45-4a04-a62b-7a4fc805e744",
  "user": "[email protected]",
  "version": 4
}

When Enhanced Session Recording is enabled, the session.end event emitted when a session ends will also include the "enhanced_recording": true field, similar to the following:

{
  "code": "T2004I",
  "ei": 23,
  "enhanced_recording": true,
  "event": "session.end",
  "interactive": true,
  "namespace": "default",
  "participants": [
    "[email protected]"
  ],
  "server_id": "585fc225-5cf9-4e9f-8ff6-1b0fd6885b09",
  "sid": "ca82b98d-1d30-11ea-8244-cafde5327a6c",
  "time": "2019-12-12T22:44:46.218Z",
  "uid": "83e67464-a93a-4c7c-8ce6-5a3d8802c3b2",
  "user": "[email protected]"
}

If your Teleport cluster uses a file-based event log, you can examine your audit log on the Teleport Auth Service host.

Is my cluster using a file-based event log?

Teleport's session recordings backend is configured via the teleport.storage.audit_sessions_uri field. If a provided URI includes a scheme that belongs to a cloud-based service (e.g., s3:// or dynamodb://), you will not be able to inspect session recordings in the filesystem of your Auth Service host.

Examine the contents of /var/lib/teleport/log as shown below:

$ teleport-auth ~:  tree /var/lib/teleport/log
# /var/lib/teleport/log
# ├── 1048a649-8f3f-4431-9529-0c53339b65a5
# │   ├── 2020-01-13.00:00:00.log
# │   └── sessions
# │       └── default
# │           ├── fad07202-35bb-11ea-83aa-125400432324-0.chunks.gz
# │           ├── fad07202-35bb-11ea-83aa-125400432324-0.events.gz
# │           ├── fad07202-35bb-11ea-83aa-125400432324-0.session.command-events.gz
# │           ├── fad07202-35bb-11ea-83aa-125400432324-0.session.network-events.gz
# │           └── fad07202-35bb-11ea-83aa-125400432324.index
# ├── events.log -> /var/lib/teleport/log/1048a649-8f3f-4431-9529-0c53339b65a5/2020-01-13.00:00:00.log
# ├── playbacks
# │   └── sessions
# │       └── default
# └── upload
#    └── sessions
#        └── default

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​