# Input Validation Injection

> Apply when reviewing or writing code that processes untrusted input, constructs queries or commands, or handles user-supplied data. Covers SQL, LDAP, OS command injection, prototype pollution, and general validation strategy.

- Skill: `backspace-shmackspace/input-validation-injection` (Agent Skill)
- Install (CLI): `npx skillmds@latest add backspace-shmackspace/input-validation-injection`
- Raw SKILL.md: https://api.skillmd.com/api/skills/backspace-shmackspace/input-validation-injection/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Data & Analytics
- Author: backspace-shmackspace (https://skillmd.com/u/backspace-shmackspace)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/backspace-shmackspace/input-validation-injection

---


# Input Validation and Injection Defense

Ensure untrusted input is validated and never interpreted as code. Prevent injection across SQL, LDAP, OS commands, templating, and JavaScript runtime object graphs.

## Core Strategy

- Validate early at trust boundaries with positive (allow-list) validation and canonicalization.
- Treat all untrusted input as data, never as code. Use safe APIs that separate code from data.
- Parameterize queries/commands; escape only as last resort and context-specific.

## Validation Playbook

- **Syntactic validation**: enforce format, type, ranges, and lengths for each field.
- **Semantic validation**: enforce business rules (e.g., start <= end date, enum allow-lists).
- **Normalization**: canonicalize encodings before validation; validate complete strings (regex anchors `^$`); beware ReDoS.
- **Free-form text**: define character class allow-lists; normalize Unicode; set length bounds.
- **Files**: validate by content type (magic), size caps, and safe extensions; server-generate filenames; scan; store outside web root.

## SQL Injection Prevention

- Use prepared statements and parameterized queries for 100% of data access.
- Use bind variables for any dynamic SQL within stored procedures -- never concatenate user input into SQL.
- Prefer least-privilege DB users and views; never grant admin to app accounts.
- Escaping is fragile and discouraged; parameterization is the primary defense.

Example (Java PreparedStatement):

```java
String custname = request.getParameter("customerName");
String query = "SELECT account_balance FROM user_data WHERE user_name = ? ";
PreparedStatement pstmt = connection.prepareStatement(query);
pstmt.setString(1, custname);
ResultSet results = pstmt.executeQuery();
```

## LDAP Injection Prevention

- Always apply context-appropriate escaping:
  - DN escaping for `\ # + < > , ; " =` and leading/trailing spaces
  - Filter escaping for `* ( ) \ NUL`
- Validate inputs with allow-lists before constructing queries; use libraries that provide DN/filter encoders.
- Use least-privilege LDAP connections with bind authentication; avoid anonymous binds for application queries.

## OS Command Injection Defense

- Prefer built-in APIs instead of shelling out (e.g., library calls over `exec`).
- If unavoidable, use structured execution that separates command and arguments (e.g., ProcessBuilder). Do not invoke shells.
- Strictly allow-list commands and validate arguments with allow-list regex; exclude metacharacters (`& | ; $ > < \ ! ' " ( )` and whitespace as needed).
- Use `--` to delimit arguments where supported to prevent option injection.

Example (Java ProcessBuilder):

```java
ProcessBuilder pb = new ProcessBuilder("TrustedCmd", "Arg1", "Arg2");
Map<String,String> env = pb.environment();
pb.directory(new File("TrustedDir"));
Process p = pb.start();
```

## Query Parameterization Guidance

- Use the platform's parameterization features (JDBC PreparedStatement, .NET SqlCommand, Ruby ActiveRecord bind params, PHP PDO, SQLx bind, etc.).
- For stored procedures, ensure parameters are bound; never build dynamic SQL via string concatenation inside procedures.

## Prototype Pollution (JavaScript)

- Use `new Set()` or `new Map()` instead of object literals.
- When objects are required, create with `Object.create(null)` or `{ __proto__: null }` to avoid inherited prototypes.
- Freeze or seal objects that should be immutable; consider Node `--disable-proto=delete` as defense-in-depth.
- Avoid unsafe deep merge utilities; validate keys against allow-lists and block `__proto__`, `constructor`, `prototype`.

## Caching and Transport

- Apply `Cache-Control: no-store` on responses containing sensitive data; enforce HTTPS across data flows.

## Implementation Checklist

- [ ] Central validators: types, ranges, lengths, enums; canonicalization before checks
- [ ] 100% parameterization coverage for SQL; dynamic identifiers via allow-lists only
- [ ] LDAP DN/filter escaping in use; inputs validated prior to query
- [ ] No shell invocation for untrusted input; if unavoidable, structured exec + allow-list + regex validation
- [ ] JS object graph hardened: safe constructors, blocked prototype paths, safe merge utilities
- [ ] File uploads validated by content, size, and extension; stored outside web root and scanned

## Test Plan

- Static checks for string concatenation in queries/commands and dangerous DOM/merge sinks.
- Fuzzing for SQL/LDAP/OS injection vectors; unit tests for validator edge cases.
- Negative tests exercising blocked prototype keys and deep merge behavior.