Pulse/docs/AGENT_SECURITY.md

Agent Security

Pulse agents incorporate several security mechanisms to ensure that the code running on your infrastructure is authentic and untampered with.

Start with the least privilege that answers your monitoring question. For Proxmox VE, PBS, and PMG, that is usually no agent at all: API-only monitoring with a read-only token covers inventory, status, and metrics, and the generated setup script creates a privilege-separated monitoring user for it (see Proxmox Deployment Choices). Install a host agent only where you want data the platform API cannot provide, and on Linux consider the supported least-privilege profile before the root default.

Agent Privilege Model

Pulse's Linux/systemd installer runs the unified agent as root by default. That is intentional for full host telemetry: disk SMART data, mdadm/RAID state, temperature sensors, Docker or Podman socket reads, Proxmox host-local details that are not available through the API, and some NAS/platform integrations commonly require root or equivalent local privileges. On Linux/systemd hosts, the supported alternative is the least-privilege profile documented below; it trades the root-only collectors it has not been granted for a dedicated non-root service user.

Treat a host agent like other infrastructure monitoring software with local root read access:

• install it only on hosts you trust Pulse to monitor;
• keep the agent token scoped to that Pulse server;
• keep the local command-authority profile monitoring-only unless you explicitly accept the transitional combined command runtime;
• update from signed release assets rather than arbitrary branch snapshots.

The agent is primarily an outbound reporter to your Pulse server. By default it binds the health and Prometheus endpoints to 127.0.0.1:9191, so a root agent does not expose that HTTP surface to the network unless you explicitly opt in. Set --health-addr :9191 only when you intentionally scrape the agent from another host. Use --health-addr "" or PULSE_HEALTH_ADDR=off to disable the listener.

Generated Linux/systemd units also include conservative sandboxing such as NoNewPrivileges=true, PrivateTmp=true, kernel/control-group write protection, a private umask, and setuid/personality restrictions. Those directives reduce service blast radius while keeping the filesystem and device access needed for full host telemetry, Proxmox token setup, SMART, Docker, and NAS integrations.

Disk monitoring normally filters pseudo-filesystems such as tmpfs. The local --disk-include option can opt a specific device or mount point back into capacity monitoring, for example a log2ram /var/log mount. This reports filesystem capacity and usage metadata. It does not read or transmit file contents. Local --disk-exclude rules still take precedence.

Fresh installs use a local monitoring-only command-authority ceiling and a credential without agent:exec. Remote configuration cannot promote that service. Selecting the advanced legacy combined command profile at install time adds --enable-commands, records command-capable, and issues an execution- scoped credential. The root monitoring process can then also accept server command requests through the existing policy and approval surfaces. Existing unmarked services upgrade as legacy during the migration window so upgrades do not silently revoke an operator's prior command choice. Agent Doctor shows the process privilege, local authority ceiling, and credential execution scope separately and warns about mismatches.

Custom numeric sensors are a separate, local configuration boundary. Enabling them with --custom-sensors-file does not enable remote commands and --enable-commands is not required. The server cannot add or alter a custom sensor command. The agent accepts only absolute executable paths with no arguments or shell interpretation, bounds concurrency, time, and output, and revalidates the command before every run. On POSIX systems the configuration, commands, and immediate command directories must pass ownership, symlink, and write-permission checks. Treat the configured executables as trusted agent code: the service commonly runs as root, so only administrators should be able to replace them.

Agent command tokens must be bound to a host or agent identity before command registration is accepted. Pulse-minted install-command tokens for the generic host and Proxmox flows are the only first-use exception: because the server mints them before the installer knows the final hostname, Pulse binds them to the first command agent that registers with that token. Those tokens also carry the operator's command-policy choice into the first accepted report so a stale policy from an earlier installation cannot immediately disable the replacement agent. Generic unbound agent:exec tokens still fail closed.

Proxmox Deployment Choices

You do not need a Pulse agent on every Proxmox-related host just to see basic cluster inventory and utilization. Start with the least-privilege path that answers your monitoring question:

Goal	Recommended path	Root agent needed?
PVE/PBS/PMG inventory, node status, VM/container status, storage usage, and normal Proxmox API metrics	Add the Proxmox connection with a read-only or narrowly scoped API token	No
VM guest disk and memory details through QEMU Guest Agent	Use Proxmox API permissions such as VM.GuestAgent.Audit and VM.GuestAgent.FileRead where supported	No host agent for the Proxmox node
All mounted LXC filesystem capacities and usage	Install the Unified Agent on the owning PVE node; it automatically uses bounded pct list and pct df reads for running LXCs	Yes, on the PVE node
Docker/Podman containers inside a VM or LXC through guest-local reporting	Install the agent inside that VM/LXC with Docker/Podman monitoring enabled, or use another explicit guest access/reporting path	Usually requires root or Docker socket-equivalent access
Docker containers inside an LXC from a Proxmox host agent	Turn on Discover Docker in LXC guests in Settings → System → General (admin only), or start Pulse with PULSE_ENABLE_PROXMOX_GUEST_DOCKER_INVENTORY=true to lock it on; optionally limit guests with PULSE_PROXMOX_GUEST_DOCKER_INVENTORY_VMIDS=101,102	Requires a root/equivalent Pulse agent on the Proxmox node and explicit server opt-in
Host SMART, temperatures, local ZFS/Ceph/mdadm detail, arbitrary mount reads, and full host telemetry	Install the agent on that host	Yes, for the supported full-telemetry profile
Kubernetes node/pod monitoring from a cluster	Use the Kubernetes agent/DaemonSet profile	Depends on whether host metrics are enabled

Inside-guest runtime visibility is explicit. Installing the agent inside a VM or LXC authorizes that guest-local agent to report Docker/Podman monitoring data according to its local module flags. A Proxmox node agent does not look inside LXCs by default. Its automatic LXC filesystem collector is a node-local capacity query only: it runs pct list, then pct df <vmid> for guests already reported running, and reports mount keys, volume labels, mount paths, and capacity/usage numbers. It does not run a command inside the guest or read guest files, processes, environment, or container-runtime metadata. It skips guests reported stopped and bounds command time, output, guest count, and disk count.

The node agent can collect Docker container inventory from LXC guests through pct exec, but only after an explicit server-side opt-in: the admin-only Discover Docker in LXC guests toggle in Settings → System → General, or starting the server with PULSE_ENABLE_PROXMOX_GUEST_DOCKER_INVENTORY=true (which locks the toggle). Inventory collection is disabled by default, can be VMID-allowlisted, and is limited to the Docker page summary path: Docker host/runtime version, container ID, name, image, state/status, ports, and aggregate docker stats counters. It does not run docker inspect and does not collect guest environment values, mount sources, container commands, files, or process details. The lighter socket-presence hint remains separately available through PULSE_ENABLE_PROXMOX_GUEST_DOCKER_DETECTION=true.

For VMs, a Proxmox host agent still cannot see Docker/Podman inventory without guest cooperation such as a guest-local Pulse agent, QEMU guest-agent mediated integration, SSH, or an explicitly exposed Docker/Podman reporting endpoint.

If Proxmox API data is enough for your use case, prefer API-only monitoring and do not install a host agent just because the installer exists. Install agents where you need data that Proxmox cannot provide through its API, or where the data lives inside a guest/container rather than at the Proxmox node layer. The Settings Proxmox setup flow uses this API inventory path as the default; the host telemetry agent path is for the full-telemetry cases above. Generated API Inventory setup still needs a one-time privileged shell on the Proxmox host so it can create the pulse-monitor account, token, and ACLs, but steady-state monitoring uses the Proxmox API rather than a root Pulse agent. For PVE, the generated script creates a privilege-separated API token and mirrors the generated read/monitoring ACLs onto both the service user and the token. For PBS, the generated script grants the Audit ACL to both the service user and token.

Least-Privilege Agent Profile

For a standard Linux systemd host, the stronger opt-in profile is:

install.sh --least-privilege --enable-privileged-helper ...

This profile keeps the networked collector unprivileged and keeps both the collector and helper binaries root-owned. Its installer token lives under the root-owned /etc/pulse-agent directory with root:pulse-agent group-read access; mutable identity, buffering, and enrolled monitoring-token state remain under the collector-owned state directory. The collector is not added to the rootful Docker group and cannot enable command execution. Automatic binary replacement is disabled until signed update activation moves behind a separate typed transaction, so operators must use an explicit signed installer update for this opt-in profile.

Exceptional telemetry crosses /run/pulse-agent/helper.sock to a separate root process. The socket admits only the pulse-agent UID, and the helper has no Pulse URL, API token, or network namespace. Its protocol exposes bounded, versioned SMART and Proxmox LXC filesystem snapshots, not a shell, executable path, device path, VMID, environment, or caller-selected arguments. The helper service keeps PrivateNetwork=true, RestrictAddressFamilies=AF_UNIX, NoNewPrivileges=true, ProtectSystem=strict, and ProtectHome=true. PrivateDevices is intentionally not enabled because SMART needs the host block devices. If the helper is missing, incompatible, or rejects a request, only the affected telemetry disappears; the collector does not fall back to sudo, root, or a broader local command path.

The typed-helper profile cannot be combined with --grant-smart or --grant-pct. Rootful Docker-socket monitoring is also unavailable because membership in the Docker group is root-equivalent; API monitoring or a separately scoped rootless runtime socket is required instead. The profile is currently explicit rather than the installer default while migration, rollback, update activation, appliance qualification, and the separate action runner are completed.

The older --least-privilege profile without --enable-privileged-helper remains available for compatibility. Its trade-offs are documented below.

On standard Linux systemd hosts, install.sh --least-privilege is a supported alternative to the root profile. It runs the service as a dedicated pulse-agent system user (nologin shell, owning only its state directory and binary), joins the docker group when Docker monitoring is enabled so socket reads keep working, and keeps every hardening directive of the root unit while dropping the LXC-attach ambient capability grant entirely.

Two optional flags restore the collectors that genuinely need elevation, each through an exact-command sudoers grant validated with visudo and a root-owned wrapper the agent is pointed at via an absolute-path-only environment override. Because NoNewPrivileges blocks sudo entirely, a unit with an active grant sets NoNewPrivileges=false while keeping the remaining hardening; a grantless least-privilege install keeps NoNewPrivileges=true. Choose grants deliberately: each one is a scoped, auditable widening of the profile.

• --grant-smart allows exactly smartctl, restoring SMART disk health.
• --grant-pct allows exactly pct list and pct df, restoring Proxmox LXC filesystem capacity. The grant deliberately excludes pct exec, start, stop, and enter, so guest Docker inventory stays a root-profile feature.

What the profile gives up: command execution (--enable-commands is refused and a later server-side enable requires reinstalling the root profile), pct exec guest Docker inventory, and any platform integration that needs device or socket access you have not granted. Core metrics, mounts, /proc RAID state, hwmon temperatures, and Docker socket reads work without root. Ungranted collectors fail soft, and the agent reports its privilege profile so Settings → Infrastructure → Agent Doctor shows the service user and active helpers instead of presenting missing collectors as a fault. Appliance platforms (TrueNAS, Synology, QNAP, Unraid) and non-systemd init systems keep the root profile; the installer refuses --least-privilege there rather than silently falling back to root.

--update preserves either installed least-privilege profile without the flags being repeated. Uninstall removes the typed helper socket/service and its installer credential directory, or the legacy sudoers file and wrappers; the inert system user is left behind deliberately.

Supply-Chain Boundary

The agent self-update path is not just "download the latest binary and run it". Release builds require checksum validation, and when trusted update keys are embedded they also require an Ed25519 release signature before replacing the running binary.

The initial installer is different: if you paste and run a shell command as root, you are granting root to that installer at that moment. Prefer the release-pinned, signature-verified server installer flow documented in README.md and INSTALL.md, then use the agent install command generated by your own Pulse server.

For the server installer, avoid latest when you want a tighter change-control boundary. Download a specific release tag, verify the install.sh.sshsig signature, and pass that same tag to bash install.sh --version. Agent self-updates still verify checksum headers, and release builds require signatures when a trusted update key is embedded.

The first automatic hop from an already-installed v5 pulse-agent to v6 is performed by the v5 updater. That updater verifies TLS by default, requires the server-provided SHA-256 checksum, validates executable magic, enforces the size limit, and swaps atomically, but it does not yet have the v6 Ed25519 signature requirement or downloaded-binary --self-test. For that migration hop, use HTTPS or a trusted local network. In high-assurance environments, reinstall the v6 pulse-agent through the signed installer path instead of relying on the automatic v5-to-v6 first hop over plain HTTP.

Self-Update Security

The agent's self-update mechanism is critical for security and stability. To prevent supply chain attacks or compromised update servers from distributing malicious or broken agents, Pulse employs a rigorous verification process.

1. Checksum Verification

The agent verifies a SHA-256 checksum of the downloaded binary. The server must provide X-Checksum-Sha256; updates are rejected if the header is missing or mismatched.

2. Signature Verification

Release builds embed trusted Ed25519 update public keys and require X-Signature-Ed25519 in addition to the checksum header. Updates are rejected when the signature is missing or does not verify against the embedded trust root.

3. Pre-Flight Checks

To prevent "brick-updates"—bad updates that crash immediately and require manual recovery—agents perform pre-flight validation before replacing the running executable.

Unified agent (pulse-agent):

1. Download new binary.
2. Verify checksum (required).
3. Verify the Ed25519 release signature when trusted update keys are embedded.
4. Validate binary magic (ELF/Mach-O/PE) and size limits (100MB max).
5. Run the downloaded binary with --self-test, passing any live token through a short-lived 0600 token file rather than argv.
6. Make executable and swap atomically.

API Security

• Token Authentication: All agent-to-server communication requires a valid API token.
• TLS: Encrypted by default (unless specifically disabled).
• Network Isolation (optional): The agent control plane can be served on a dedicated, separately firewalled port. It exposes the bounded report/config, command WebSocket, version, and bootstrap routes needed for the full agent lifecycle, but not the web UI or management API. See Split-Port Agent Ingest.