eng-pad-server/AUDIT.md

AUDIT.md — eng-pad-server Security Audit

Audit Date: 2026-03-24

Summary

Comprehensive security and engineering review of the eng-pad-server codebase. 17 issues identified across critical, high, and medium severity levels. All critical and high issues resolved.

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Findings

A-001: SQL Injection in Database Backup

• Severity: Critical
• Status: Resolved
• Location: cmd/eng-pad-server/snapshot.go
• Description: Backup path interpolated into SQL via fmt.Sprintf without escaping. Allows arbitrary SQL execution if path contains single quotes.
• Resolution: Escape single quotes in the backup path before interpolation.

A-002: Authentication Timing Attack

• Severity: High
• Status: Resolved
• Location: internal/auth/users.go
• Description: Early return when user not found skips Argon2id computation, allowing username enumeration via response timing.
• Resolution: Always perform Argon2id verification against a dummy hash when user is not found, consuming constant time.

A-003: Missing Notebook Ownership Checks

• Severity: High
• Status: Resolved
• Location: internal/server/notebooks_handler.go
• Description: Authenticated endpoints load notebooks by ID without verifying the notebook belongs to the requesting user. An authenticated user could access any notebook by guessing IDs.
• Resolution: Added user_id check to all notebook queries in authenticated endpoints. Share link endpoints use the validated notebook ID from the share link.

A-004: Unbounded Point Data Decoding

• Severity: High
• Status: Resolved
• Location: internal/render/svg.go
• Description: decodePoints() panics on data not aligned to 4 bytes, has no size limit (OOM risk), and doesn't filter NaN/Inf.
• Resolution: Added alignment check, 4MB size limit, NaN/Inf filtering. Function now returns error.

A-005: Error Messages Leak Information

• Severity: High
• Status: Resolved
• Location: Multiple REST handlers
• Description: err.Error() concatenated directly into HTTP JSON responses, leaking database structure and internal state.
• Resolution: All error responses use generic messages. Detailed errors logged server-side only.

A-006: No Authorization on Share Link Revocation

• Severity: High
• Status: Resolved
• Location: internal/grpcserver/share.go
• Description: Any authenticated user could revoke any share link by token, regardless of notebook ownership.
• Resolution: Added JOIN with notebooks table to verify the calling user owns the notebook before allowing revocation.

A-007: Silent Row Scan Errors

• Severity: High
• Status: Resolved
• Location: Multiple handlers
• Description: continue on row scan errors silently returns incomplete data without indication.
• Resolution: Scan errors now return 500 Internal Server Error in REST handlers.

A-008: Web Server Missing TLS

• Severity: Medium
• Status: Resolved
• Location: internal/webserver/server.go
• Description: Web UI served over plain HTTP. Session cookies marked Secure: true are ineffective without TLS.
• Resolution: Added TLS cert/key fields to web server config. Uses HTTPS when configured, falls back to HTTP for development.

A-009: Missing Input Validation in Sync RPC

• Severity: Medium
• Status: Resolved
• Location: internal/grpcserver/sync.go
• Description: No validation of page_size, stroke count, or point data alignment in SyncNotebook RPC.
• Resolution: Added validation: page_size must be REGULAR or LARGE, total strokes limited to 100,000, point_data must be 4-byte aligned.

A-010: No Graceful Shutdown

• Severity: Medium
• Status: Resolved
• Location: cmd/eng-pad-server/server.go
• Description: Signal handler terminates immediately without draining in-flight requests.
• Resolution: Graceful shutdown with 30-second timeout: gRPC GracefulStop, HTTP Shutdown, database Close.

A-011: Missing CSRF Protection on Web Forms

• Severity: Medium
• Status: Accepted
• Rationale: Web UI is currently read-only (viewing synced notebooks). The only mutating form is login, which is not a CSRF target (attacker gains nothing by logging victim into their own account). Will add CSRF tokens when/if web UI gains write features.

A-012: WebAuthn Sign Count Not Verified

• Severity: Medium
• Status: Accepted
• Rationale: Sign count regression detection is defense-in-depth against cloned authenticators. Risk is low for a personal service. Will add verification when WebAuthn is fully wired into the web UI.

A-013: gRPC Per-Request Password Auth

• Severity: Medium (audit assessment) / Accepted (our assessment)
• Status: Accepted
• Rationale: By design. Password travels over TLS 1.3 (encrypted), stored in Android Keystore (hardware-backed). Sync is manual and infrequent. Token-based auth adds complexity without meaningful security gain for this use case.

A-014: No Structured Logging

• Severity: Medium
• Status: Open
• Description: Only fmt.Printf to stdout. No log levels, no structured output, no request tracking.
• Plan: Add log/slog based logging in a future phase.

A-015: Incomplete Config Validation

• Severity: Medium
• Status: Resolved
• Description: TLS files not checked for existence at startup. Token TTL, WebAuthn config not validated.
• Resolution: Split validation into validateFields() and validateFiles(). Added checks for: TLS file existence, token TTL parseability and positivity, Argon2 params > 0, valid log level, non-empty listen addresses. Full test coverage in config_test.go.

A-016: Inconsistent Error Types

• Severity: Low
• Status: Open
• Description: String errors instead of sentinel errors make error handling difficult for callers.

A-017: No Race Condition Testing

• Severity: Low
• Status: Resolved
• Description: Test suite does not use -race flag.
• Resolution: Added make test-race target that runs go test -race ./....

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Priority Summary

ID	Severity	Status
A-001	Critical	Resolved
A-002	High	Resolved
A-003	High	Resolved
A-004	High	Resolved
A-005	High	Resolved
A-006	High	Resolved
A-007	High	Resolved
A-008	Medium	Resolved
A-009	Medium	Resolved
A-010	Medium	Resolved
A-011	Medium	Accepted
A-012	Medium	Accepted
A-013	Medium	Accepted
A-014	Medium	Open
A-015	Medium	Resolved
A-016	Low	Open
A-017	Low	Resolved

Design Note: Single-User Model

This server is designed for a single authenticated user. The users table and multi-user schema exist but are used for one account only. If multi-user support is ever needed, authentication will migrate to MCIAS (Metacircular Identity and Access Service) — the standalone auth implementation here will not be extended for multiple users.