pilens/docs/security.md

Security and privacy model

Captured traffic can contain credentials, tokens, private messages, and medical or financial data. PiLens treats the appliance as a privileged, sensitive system.

Trust boundaries

Boundary	Untrusted side	Controls
Browser ↔ pilens	Management network	TLS, source allow-list (nftables and middleware), Argon2id passwords, session cookies Secure; HttpOnly; SameSite=Strict, CSRF token header, login throttling, optional TOTP, audit log
AP clients ↔ Pi	Wi-Fi network	nftables drops everything except DHCP, DNS and ICMP. Management is unreachable even through the uplink address.
pilens ↔ pilens-helper	pilens process	Unix socket 0660 root:pilens. SO_PEERCRED uid check. Fixed operations only. The helper re-validates the full config. Requests are capped at 1 MiB.
Packet data ↔ parsers	Anyone on the wire / uploaded files	Our pcap/pcapng readers bounds-check every length (16 MiB block cap). tshark runs via rlimit-exec (RLIMIT_AS, RLIMIT_CPU, no core dumps, no_new_privs) with a timeout and empty environment.
Packet data ↔ browser	Packet content	Rendered as text nodes by React. No dangerouslySetInnerHTML and no HTML preview. CSP default-src 'self', frame-ancestors 'none'.
Uploads	Uploaded file	Size limit enforced while streaming. Magic-number check (pcap/pcapng only, no archives, so no decompression bombs). Server-generated file names, so no path traversal. Session IDs are strictly whitelisted (^[0-9TZ]{16}-[0-9a-f]{6}$).

Privilege separation

• pilens (user pilens): no root and no ambient capabilities. Capture uses dumpcap, whose file capabilities are granted to group wireshark, which is Debian's standard model. The unit's CapabilityBoundingSet=CAP_NET_RAW CAP_NET_ADMIN limits what any child can ever gain. NoNewPrivileges cannot be set because it would disable dumpcap's file capabilities. ProtectSystem=strict leaves only /var/lib/pilens writable.
• pilens-helper (root): about 400 lines. It can write the PiLens NM keyfile, its own state directory and ip_forward; run nft, nmcli, iw and systemctl with fixed argv; and nothing else. There is no generic command execution.
• pilens-dnsmasq: Debian's dnsmasq, which drops privileges itself.

Secrets

Secret	Where	Exposure
Admin password	Argon2id hash in SQLite (0640 pilens)	Never returned
Session tokens	Only the SHA-256 is stored	Cookie only
Wi-Fi passphrase	SQLite + helper state (0600 root) + NM keyfile (0600 root)	Write-only in the API. Never in a process argv. Redacted in diagnostics.
Setup token	/var/lib/pilens/setup-token (0600)	Deleted when the first admin is created
Management TLS key	/var/lib/pilens/tls/mgmt.key (0600)	Never exported. Separate from any future interception CA.

Data protection

• PiLens currently stores no decrypted payloads, because it decrypts nothing.
• Captures are deleted by retention (oldest unpreserved first) or explicitly by an admin, who must confirm. Deleting a session removes its files and all index rows.
• Exports, deletions, configuration changes, logins (including failures), password/TOTP changes and setup are recorded in the audit log.
• No telemetry. The only outbound traffic the appliance generates is what the OS already does (apt, NTP) and the DNS forwarding it performs for AP clients.

Reviewed attack classes

Class	Mitigation
Command injection	All execs use argv lists, never a shell. Filter strings are passed as single arguments and checked for control characters. Interface names are matched against ^[A-Za-z0-9_.-]{1,15}$.
Config injection (dnsmasq/NM keyfile)	Every rendered value is strictly validated (SSID charset, hostnames as RFC 1123 labels, IPs parsed), so newlines cannot reach a config file.
SQL injection	Parameterised queries only
Path traversal	IDs are server-generated and whitelisted. Segment file names come from the database, not the client.
XSS via packet content	React text rendering, CSP, no HTML rendering of captured data
SSRF	The server makes no outbound requests based on user input
Auth bypass	Every /api/* route except health, setup status, first-admin creation and login goes through requireAuth. The setup endpoint needs the setup token, and the INSERT is conditional on no user existing (race-safe).
Resource exhaustion	Bounded SSE queues (slow clients drop updates, never capture). Bounded tshark feed. Per-process rlimits. Upload and request size limits. Storage quota and reserve. Filter cache capped at 16 entries.
Malicious pcap	Bounds-checked block reader, fuzz-style malformed-input tests, tshark resource limits
Lock-out	The API refuses a management configuration that would exclude the caller's own address

Dependency inventory: Go modules modernc.org/sqlite, golang.org/x/crypto (Argon2id) and gopkg.in/yaml.v3; npm packages react and react-dom, plus vite and typescript at build time. Run govulncheck ./... and npm audit before each release.