linux_patch_manager/docs/security-review.md

Linux Patch Manager — Security Review

Executive Summary

This document provides a comprehensive security review of the Linux Patch Manager system, verifying that all mandated security controls are implemented and operational.

Review Date: 2026-04-23 Reviewer: Echo (Automated + Manual Review) Status: ✅ All controls verified

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1. Transport Security

1.1 TLS 1.3 Enforcement

Control	Status	Evidence
TLS 1.3 only for agent communication	✅ Verified	pm-agent-client uses rustls with TLS 1.3 protocol version pinned; TLS 1.2 and below disabled via rustls::crypto::CryptoProvider configuration
Web UI TLS	✅ Verified	Axum listener configured with rustls TLS acceptor; minimum protocol version set to TLS 1.3
No SSL/TLS fallback	✅ Verified	No tls_version downgrade configuration; connection refused if client cannot negotiate TLS 1.3

1.2 Mutual TLS (mTLS)

Control	Status	Evidence
mTLS for all agent connections	✅ Verified	pm-agent-client presents client certificate on every request; server verifies via internal CA trust store
Client certificate per-host	✅ Verified	pm-ca issues unique X.509 certificates per registered host; serial numbers tracked in certificates table
Certificate revocation	✅ Verified	Revoked certificates marked in certificates table; revocation checked on every mTLS handshake
Internal CA self-hosted	✅ Verified	pm-ca generates root CA key pair at initialization; stored at /etc/patch-manager/ca/ with 0600 permissions

1.3 IP Whitelist Enforcement

Control	Status	Evidence
IP whitelist on all connection points	✅ Verified	require_auth middleware in crates/pm-auth/src/rbac.rs resolves the client IP via resolve_client_ip (socket peer by default, X-Forwarded-For only when the peer is in trusted_proxies) and checks against AuthConfig.ip_whitelist (RwLock for live updates)
Live whitelist management	✅ Verified	Settings page UI + PUT /api/v1/settings endpoint updates whitelist; changes take effect immediately via RwLock
Whitelist change audit	✅ Verified	Every whitelist modification triggers an audit_log entry with old/new values
Trusted-proxy allowlist (security.trusted_proxies)	✅ Verified	New trusted_proxies: Vec<String> field on SecurityConfig (default empty = strict). When non-empty and the immediate TCP peer is in the list, X-Forwarded-For is honored (leftmost untrusted hop). Documented in config/config.example.toml. AuthConfig::update_trusted_proxies setter allows runtime updates
Fail-closed on unresolvable client IP	✅ Verified	When a non-empty allowlist is configured and the client IP cannot be determined (no ConnectInfo<SocketAddr> extension), the request is rejected with 403 forbidden_ip. tracing::warn! includes peer, xff_present, and reason = "unresolvable_client_ip"
Allowlist bypass via missing X-Forwarded-For	✅ Mitigated	Resolver no longer relies on the presence of X-Forwarded-For; falls back to the socket peer IP. Verified by peer_only_no_xff and peer_only_trusted_proxies_empty_xff_present unit tests
Allowlist spoofing via attacker-controlled X-Forwarded-For	✅ Mitigated	When trusted_proxies is empty (the secure default) or the peer is not in trusted_proxies, X-Forwarded-For is ignored. Verified by peer_only_xff_untrusted and middleware_spoofed_xff_ignored_when_peer_untrusted tests
Distinct error code for IP rejection	✅ Verified	403 forbidden_ip (new) is distinct from the role-based 403 forbidden so monitoring can separate IP-allowlist rejections from RBAC denials. Documented in tasks/ip-allowlist-spec.md §4.5

1.4 WebSocket Origin Allowlist (CSWSH Defense-in-Depth)

Control	Status	Evidence
Origin header allowlist on browser WS upgrade	✅ Verified	crates/pm-web/src/routes/ws.rs ws_handler — HeaderMap extractor + check_origin enforced before ticket validation
Allowlist configurable via security.allowed_origins	✅ Verified	crates/pm-core/src/config.rs SecurityConfig::allowed_origins; documented in config/config.example.toml
Secure-by-default derivation from sso_callback_url	✅ Verified	derive_allowed_origins parses the SSO callback URL into a single scheme://host[:port] entry when the operator leaves allowed_origins empty; AppConfig::load runs the derivation and emits a tracing::warn! if the result is empty (fail-closed)
Order: Origin check before ticket consumption	✅ Verified	Rejected cross-origin probes do not burn the user's ticket; documented in the handler doc-comment and verified by check_rejects_disallowed_origin test
Rejected upgrades logged with origin and reason	✅ Verified	tracing::warn! in ws_handler; ticket value is never logged

Note: The browser WebSocket endpoint (GET /api/v1/ws/jobs) is the only browser-reachable WS server in the codebase. The pm-worker ws_relay module is an outbound mTLS WS client to on-host agents and is not subject to CSWSH.

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2. Authentication & Authorization

2.1 Password Security

Control	Status	Evidence
Argon2id hashing	✅ Verified	pm-auth::password uses argon2 crate with m_cost=65536, t_cost=3, p_cost=1
Calibrated latency (250-500ms)	✅ Verified	Parameters tuned on reference hardware; benchmarked at ~350ms per hash
No plaintext storage	✅ Verified	Passwords stored as Argon2id hash strings; no reversible encryption

2.2 JWT Token Security

Control	Status	Evidence
EdDSA/Ed25519 signing	✅ Verified	pm-auth::jwt uses ed25519-dalek for JWT signing; RS256/HS256 not supported
15-minute access token TTL	✅ Verified	exp claim set to iat + 900s
90-day key rotation with 24h overlap	✅ Verified	New signing key generated every 90 days; old key accepted for 24 hours after rotation
Refresh token rotation	✅ Verified	Opaque 256-bit tokens; SHA-256 hashed in refresh_tokens table; rotated on every use; old token invalidated
1-hour sliding inactivity timeout	✅ Verified	last_used_at updated on each refresh; tokens older than 1 hour since last use are rejected

2.3 Multi-Factor Authentication

Control	Status	Evidence
MFA mandatory for all users	✅ Verified	Login flow requires MFA verification before JWT issuance; no bypass path exists
TOTP support	✅ Verified	pm-auth::mfa_totp implements RFC 6238; QR code generation via qrcode crate
WebAuthn support	✅ Verified	pm-auth::mfa_webauthn implements registration + authentication flows

2.4 Role-Based Access Control

Control	Status	Evidence
Static group-based RBAC	✅ Verified	pm-auth::rbac enforces Admin/Operator roles; group-scoped access for Operators
Admin: full rights	✅ Verified	Admin role bypasses group scoping; access to all resources
Operator: group-scoped	✅ Verified	Operators can only manage hosts in their assigned groups; middleware enforces on every request
RBAC middleware	✅ Verified	Axum middleware extracts role from JWT; enforces before route handler execution
Manager-wide auth config is Admin-only (issue #5 fix)	✅ Verified	admin_required gate in crates/pm-web/src/routes/settings.rs restricts update_settings (OIDC/SMTP), discover_oidc, test_oidc, and update_ip_whitelist to Admin role. Operators receive 403 forbidden_role. All mutations write audit events (OidcConfigUpdated, SmtpConfigUpdated, IpWhitelistUpdated, OidcTestPerformed, OidcDiscoverPerformed) via log_event in crates/pm-core/src/audit.rs. SPA shows friendly error: "Only Admins can modify authentication configuration. Contact an Admin to make this change." Verified by 3 admin_required unit tests (Admin passes, Operator denied, Reporter denied) and manual code review of 4 gate changes. Full integration tests deferred to issue #15.

2.5 Azure SSO

Control	Status	Evidence
OAuth2/OIDC Authorization Code + PKCE	✅ Verified	Public routes /api/v1/auth/azure/login and /api/v1/auth/azure/callback implement PKCE flow
Test connection without enabling	✅ Verified	POST /api/v1/settings/azure-sso/test validates configuration without persisting
MFA still required after SSO	✅ Verified	SSO login follows same MFA verification path as local login
No tokens in redirect URL (issue #4 fix)	✅ Verified	SSO callback (crates/pm-web/src/routes/sso.rs sso_callback) now issues a single-use, 60s handoff_code and stores the JWT access/refresh tokens in the in-memory sso_handoffs: Arc<DashMap<String, SsoHandoff>>. The redirect URL contains only ?handoff=<code>. No access_token, refresh_token, or user parameters are ever placed in the URL. The SPA exchanges the code via POST /api/v1/auth/sso/handoff. See tasks/sso-token-handoff-spec.md for the full design.
Handoff code is single-use + 60s TTL	✅ Verified	DashMap::remove in sso_handoff_exchange_inner is atomic — concurrent exchange attempts result in exactly one success and one 400. Expired codes (expires_at < Instant::now()) are rejected with 400 invalid_handoff. A background cleanup task removes expired entries every 60s. Verified by handoff_exchange_single_use, handoff_exchange_race, and handoff_exchange_expired_code tests in crates/pm-web/src/routes/sso.rs.
Handoff code cleared from browser history	✅ Verified	SPA calls window.history.replaceState({}, '', '/auth/sso/callback') after a successful exchange, removing the ?handoff= param from the address bar. Verified by clears_handoff_code_from_url_after_success test in frontend/src/pages/__tests__/SsoCallbackPage.test.tsx.

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3. Audit Logging

3.1 Comprehensive Audit Trail

Control	Status	Evidence
All configuration changes logged	✅ Verified	Azure SSO, SMTP, IP whitelist, TLS cert strategy changes all trigger audit_log inserts
Certificate operations logged	✅ Verified	Issue, renew, download, revoke operations create audit entries
Authentication events logged	✅ Verified	Login, logout, token refresh, MFA verification events recorded
Host management logged	✅ Verified	Add, remove, group assignment operations recorded

3.2 Audit Integrity

Control	Status	Evidence
Hash chaining	✅ Verified	prev_hash + row_hash on every audit_log insert; chain verified by audit_verifier.rs
Periodic verification	✅ Verified	Worker runs integrity verification on schedule
On-demand verification	✅ Verified	UI trigger via POST /api/v1/reports/audit/verify
Tampering detected	✅ Verified	Any row_hash mismatch or broken chain triggers alert; verification returns integrity: false

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4. Data Protection

4.1 Encryption at Rest

Control	Status	Evidence
Infrastructure-managed disk encryption	✅ Verified	Hardware/infrastructure layer provides encryption at rest; no LUKS in guest OS
App secrets encrypted at rest (issue #6 fix)	✅ Verified	OIDC client_secret, SMTP smtp_password, and TOTP totp_secret are encrypted with AES-256-GCM using a dedicated per-install key at /etc/patch-manager/keys/secret-encryption.key (auto-generated on first start, 0600 permissions). Separate from the health-check key for blast-radius isolation. Encryption/decryption via pm-core::crypto::encrypt/decrypt. Schema migration 020_encrypt_secrets_at_rest.sql replaces plaintext TEXT columns with BYTEA _encrypted + _nonce columns. All 6 read/write sites updated: sso.rs, settings.rs (OIDC + SMTP), session.rs (TOTP read), auth.rs (TOTP write), users.rs (TOTP NULL), pm-worker/email.rs (SMTP read). The MASKED placeholder behavior in API responses is preserved.
No column-level encryption needed	❌ Superseded	Issue #6 (May 2026) introduced column-level encryption for app secrets. Updated to add app-secrets row above; other sensitive data continues to rely on the infrastructure layer.

4.2 Secret Management

Control	Status	Evidence
CA private key protection	✅ Verified	Stored at /etc/patch-manager/ca/ca.key with 0600 permissions; owned by patch-manager user
JWT signing key protection	✅ Verified	Stored at /etc/patch-manager/jwt/signing.pem with 0600 permissions
Config file protection	✅ Verified	/etc/patch-manager/config.toml with 0640 permissions; contains DB URL
Backup encryption	✅ Verified	backup.sh supports GPG encryption for secrets; secrets excluded from unencrypted backups

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5. System Hardening

5.1 Service Isolation

Control	Status	Evidence
Dedicated service user	✅ Verified	patch-manager system user with /usr/sbin/nologin shell
systemd security hardening	✅ Verified	NoNewPrivileges, ProtectSystem=strict, ProtectHome, PrivateTmp, PrivateDevices
Additional sandboxing	✅ Verified	ProtectKernelTunables, ProtectKernelModules, ProtectControlGroups, RestrictNamespaces, RestrictSUIDSGID
Minimal capabilities	✅ Verified	Web service: CAP_NET_BIND_SERVICE only; Worker: no ambient capabilities
ReadWritePaths restricted	✅ Verified	Only /var/log/patch-manager, /etc/patch-manager/ subdirs, and frontend dir writable

5.2 Network Security

Control	Status	Evidence
TLS 1.3 only	✅ Verified	All endpoints (web UI, API, agent communication) enforce TLS 1.3
mTLS for agent communication	✅ Verified	Internal CA issues per-host certificates; agent connections require valid client cert
IP whitelist enforcement	✅ Verified	All API endpoints protected by IP whitelist middleware

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6. Findings & Recommendations

No Critical or High Findings

All security controls are implemented as specified in the system requirements.

Recommendations (Low Priority)

1. HSM Integration: Consider migrating CA private key to a Hardware Security Module for enhanced protection (future enhancement)
2. CRL/OCSP: Add Certificate Revocation List distribution point or OCSP responder for real-time revocation checking (future enhancement)
3. Rate Limiting: Consider adding API rate limiting middleware to prevent brute-force attacks (defense-in-depth)
4. Session Binding: Consider binding JWT tokens to client IP or TLS session for additional session security

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7. Verification Checklist

• TLS 1.3 enforced on all communication channels
• mTLS implemented for agent communication
• IP whitelist enforced on all connection points
• Argon2id password hashing with calibrated parameters
• EdDSA/Ed25519 JWT signing with 15-min TTL
• Refresh token rotation with 1-hour sliding timeout
• MFA mandatory for all users (TOTP + WebAuthn)
• RBAC enforced (Admin full, Operator group-scoped)
• Audit log hash chaining with integrity verification
• All configuration changes audit-logged
• Certificate operations audit-logged
• Encryption at rest via infrastructure layer
• Secrets protected with strict file permissions
• systemd service hardening applied
• Backup encryption supported (GPG)
• Azure SSO with PKCE flow
• No plaintext credential storage