---

name: security/input-validation description: Input Validation security skill

Input Validation

All external data is hostile. Validate exhaustively at trust boundaries, reject by default.

ikigai Application

Trust boundaries in ikigai:

• Terminal input (keystrokes, escape sequences)
• Config files (JSON, paths)
• LLM responses (streaming chunks)
• Environment variables

Injection vectors:

• Command injection: Never pass user strings to system() or popen()
• Path traversal: Reject .., canonicalize paths before use
• Format string: Never printf(user_input), always printf("%s", user_input)
• Null byte: Truncates C strings, bypasses extension checks

Validation principles:

• Allowlist over blocklist
• Validate type, length, format, range
• Reject on first failure
• Sanitize for context (shell, SQL, HTML, ANSI)

After validation: Internal functions can assert() preconditions. The boundary function already validated.

Review red flags: User data in format strings, string concatenation for paths/commands, unchecked lengths.