Input Validation & Injection Defense

description: Input validation and injection defense (SQL/LDAP/OS), parameterization, prototype pollution languages:

• c
• go
• html
• java
• javascript
• php
• powershell
• python
• ruby
• shell
• sql
• typescript alwaysApply: false

rule_id: codeguard-0-input-validation-injection

Input Validation & 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 construction within stored procedures and 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):

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):

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)

• Developers should use new Set() or new Map() instead of using 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.