The jump host connector image

Understand the jump host connector image — the container that runs P0's Azure function for terminating live SSH sessions — and where it is published.

The connector image is the container the jump host connector application runs. It packages a single Azure function that terminates a live SSH session on one of your jump host VMs when P0 revokes access. This page explains what the image contains, how P0 calls it, and where P0 publishes it.

Jump host management is in beta.

What the image is

The image is a Node.js Azure Function App container that P0 builds and publishes:

Property	Value
Image	p0security/p0-security-perimeter-azure-vm
Registry	Docker Hub
Default tag	latest
Runtime	Node.js, Azure Functions v4 (worker indexing)

You do not build the image. P0 builds and publishes it to Docker Hub, and your connector Function App pulls and runs it. View the published image at hub.docker.com/r/p0security/p0-security-perimeter-azure-vm.

What the function does

The image exposes one HTTP-triggered function that terminates an SSH session:

Endpoint: POST /api/kill-session

Request body:

Field	Type	Required	Description
email	string	Yes	The requestor whose session is terminated.
ip	string	Yes	The source IP of the SSH session.
port	number	No	The source port of the SSH session.
vmResourceId	string	Yes	The full Azure resource ID of the jump host VM to run the kill command on.

When P0 revokes a requestor's access, it calls this endpoint. The function then:

1. Validates the request. It enforces a strict email format, a valid IP address, and a port in the range 1–65535. These checks also guard against shell injection, because the target jump host receives these values in a shell command.

2. Runs a script on the target VM through Azure Run Command (RunShellScript). The script resolves the local account for email, finds the SSH connections from ip (and port, defaulting to 22) to that account, and terminates the matching processes.

3. Reports the outcome. Terminating a session is idempotent teardown, so "nothing to terminate" is a success, not an error. The function returns 200 whether it terminated a session, found no matching session, found no local account for the email, or found the VM stopped. It returns 500 only when the script itself fails.

Because termination uses Azure Run Command, the connector needs no inbound network path to your jump hosts and no P0-managed agent on them — it uses the standard Azure VM Guest Agent that Azure VMs run by default.

The function authorizes each Run Command with the connector Function App's system-assigned managed identity, which holds the P0 Session Terminator role on the target VM. It also emits security-event logs (LOG_SECURITY_EVENTS) so you can audit each termination in the Function App's logs.

How P0 calls the image securely

Two controls protect the function so that only P0 can invoke it:

• App Service Authentication. The Function App accepts requests only from the p0-session-terminator app registration; any other caller receives a 401 response. The function itself fails closed — it rejects any request that arrives without the platform-validated caller principal. For how this trust is established, see The jump host connector application.

• Workload identity federation. P0 authenticates without a stored secret. P0 exchanges a Google Cloud service account token for an Entra access token — scoped to api://<client-id>/.default with audience api://AzureADTokenExchange — and sends it as a bearer token. The connector's federated credential trusts only P0's service account, so no other identity can obtain a valid token.

Requirements for jump host VMs

The connector terminates sessions by running a shell script on your jump host VMs, so each managed VM must meet the following requirements. Build these into your jump host image or base configuration.

Requirement	Why
Azure VM Guest Agent installed and running	Azure Run Command dispatches the termination script through the guest agent. Standard Azure Linux images ship with it enabled.
A Linux OS with ss (from iproute2) available	The script uses ss to find the SSH connections to terminate.
SSH users provisioned as local accounts	The script matches sessions by resolving the requestor's email to a local user with getent passwd. A session for an email that has no local account is treated as already terminated.
SSH listening on the expected port	The script matches connections against the request's port, defaulting to 22. Set the connector's DEFAULT_SSH_PORT app setting if your jump hosts use a different backend port.

Azure Run Command runs the termination script as root, so no extra sudo configuration is required on the jump host.

The image's environment contract

The connector Function App sets the following app settings to match what the image expects.

Setting	Value	Purpose
FUNCTIONS_WORKER_RUNTIME	node	Selects the Node.js worker.
CALLER_APP_ID	App registration client ID	The app registration the function trusts as its caller.
LOG_SECURITY_EVENTS	true	Emits security-event logs for each termination.
WEBSITES_ENABLE_APP_SERVICE_STORAGE	false	Lets the image's baked-in function code and AzureWebJobsScriptRoot load instead of an empty Azure Files share.
AzureWebJobsFeatureFlags	EnableWorkerIndexing	Required for the v4 Node.js model so the host discovers the function's HTTP trigger.
DEFAULT_SSH_PORT	22 (optional)	The backend SSH port the termination script matches against when a request omits port. Set this if your jump hosts listen on a non-standard port.

Do not change WEBSITES_ENABLE_APP_SERVICE_STORAGE or AzureWebJobsFeatureFlags. With either set incorrectly, the host loads no functions and the connector exposes no kill-session endpoint.

Where the image is published

P0 publishes the image to Docker Hub at hub.docker.com/r/p0security/p0-security-perimeter-azure-vm. The connector Function App runs it directly from there, pulling the latest tag by default.

If your environment restricts pulls from Docker Hub, mirror the image to a registry you control, such as Azure Container Registry, and point the connector Function App at your copy. Grant the Function App's managed identity permission to pull from that registry — for example, the AcrPull role on an Azure Container Registry.

Related pages

• Jump host management

• The jump host connector application