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

🔴 CRITICAL: Committed Private Key Material (Issue #12) — RESOLVED

Description: Private key file client.key and public certificates (client.crt, ca.crt) were committed to version control in crates/pm-agent-client/certs/. Committed private keys are a critical security risk: anyone with repository access can impersonate agents or decrypt captured TLS traffic.

Status: ✅ RESOLVED

Remediation Applied:

1. Removed all cert files from git tracking (git rm --cached)
2. Added *.key, *.key.pem and crates/pm-agent-client/certs/ to .gitignore
3. Updated pm-agent-client doc examples to use std::fs::read() instead of include_bytes!
4. Added gitleaks secret scanning to CI pipeline
5. Added README to crates/pm-agent-client/certs/ explaining runtime cert generation
6. Git history will be purged with git filter-repo after PR merge

Key Rotation: These keys were dev/test only. No production key rotation is needed. All committed keys should be considered compromised and must not be used in production.

No Other Critical or High Findings

All other 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
• Committed private key material removed from repository (Issue #12)