Security Input Validation And Dangerous Sinks

Pack: security Source: security/security-input-validation-and-dangerous-sinks/SKILL.md Use this skill when the risk comes from attacker-controlled input flowing into a dangerous sink.

Scope

• input validation
• normalization
• parameterized database access
• HTML and output-context encoding
• shell, path, redirect, and URL sink safety

Default path

1. Name the untrusted input source.
2. Name the dangerous sink it can reach.
3. Validate and normalize input once near entry.
4. Use sink-specific protection:
   • parameterized queries for SQL
   • context-appropriate escaping or encoding for HTML
   • path allowlists or fixed roots for filesystem access
   • no shell interpolation for command execution
   • redirect allowlists for outbound navigation
5. Keep raw attacker input away from privileged sinks when possible.

When to deviate

• Use richer schema validation only when the domain actually needs structured coercion or refinement.
• Allow limited rich text only with a deliberate sanitization and rendering boundary.
• Use raw input logs sparingly and only with redaction when sensitive data may be present.

Guardrails

• Validation is not generic string cleaning.
• Protection must match the sink, not just the input type.
• Normalize once; avoid multiple inconsistent parsing paths.
• Prefer avoiding dangerous sinks entirely when the feature design allows it.

Avoid

• “sanitize everything” with no sink model
• string-concatenated SQL
• trusting file paths or redirect targets from raw input
• assuming one HTML sanitizer solves shell, SQL, and URL problems too

Verification checklist

• source input is named
• dangerous sink is named
• validation and normalization happen once
• sink-specific protection is used
• raw attacker input is not flowing unchecked into privileged operations

Output Shape

When answering with this skill, prefer:

• untrusted source
• dangerous sink
• required validation
• required sink-specific protection
• main exploit path if left unchanged

References

• Validation and sink defaults