# Injection

> Detects SQL, command, and template injection caused by user input reaching an interpreter without parameterization. Use when writing code that constructs database queries, builds SQL strings, executes shell commands, processes templates with user input, evaluates code dynamically, or passes user- controlled data to any external interpreter.

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

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# Injection Security Check (A05:2025)

## What this checks

Protects against SQL, command, and template injection caused by passing
user-controlled data to an interpreter without sanitization. Exploitation leads to
full database read/write, remote code execution, and data exfiltration.
For NoSQL-specific injection (MongoDB operator injection, `$where`), see `nosql-injection`.

## Vulnerable patterns

- `"SELECT * FROM users WHERE id = " + userId` — user input concatenated into SQL
- `exec("convert " + filename)` — shell expansion allows `; rm -rf /`
- `eval(userInput)` — arbitrary code execution from user-supplied string
- `Template("Hello " + name)` — template body built from user input

## Fix immediately

For each vulnerable call site, apply the appropriate control:

- **SQL**: use parameterized queries or an ORM — never concatenate user input into query strings
- **Shell**: pass arguments as an array/list, never as an interpolated string — disable shell expansion
- **Templates**: use an engine that autoescapes by default and pass user values through the parameter interface. Python: `Environment(autoescape=True)` (bool literal, not `select_autoescape()` with `from_string()`). Go: `html/template`, never `text/template` for HTTP output. Java FreeMarker: `cfg.setOutputFormat(HTMLOutputFormat.INSTANCE)`. Rust: `handlebars` (escapes by default). Never build the template body from user input.
- **eval/exec**: remove entirely — there is no safe way to evaluate user-supplied code strings

Flag the vulnerable call site, explain the risk and the correct fix pattern, then continue with the original task.

## Verification

Confirm the following *properties* hold (language-agnostic):

- [ ] User-controlled values reach SQL only as bound parameters — never via string interpolation, concatenation, or format strings
- [ ] User-controlled values reach subprocess execution only as discrete argument list elements — never via a shell string or interpolated command string
- [ ] No dynamic evaluation of user-supplied strings as code (Python `eval`/`exec`, JS `eval`/`new Function`, etc. removed — not replaced with a safer-looking variant of the same function)
- [ ] Templates use an engine where HTML autoescaping is either enabled explicitly or is the documented default (Flask `render_template`, Go `html/template`, Rust `handlebars`, Jinja2 `Environment(autoescape=True)` — NOT Jinja2 `Template()` direct, NOT Go `text/template`), and user values are passed through the engine's parameter interface — never by building the template body from user input

## References

- CWE-89 ([SQL Injection](https://cwe.mitre.org/data/definitions/89.html))
- CWE-78 ([OS Command Injection](https://cwe.mitre.org/data/definitions/78.html))
- CWE-94 ([Code Injection](https://cwe.mitre.org/data/definitions/94.html))
- [OWASP A05:2025 Injection](https://owasp.org/Top10/A03_2021-Injection/)