How to Prevent Prompt Injection in Production

How to Prevent Prompt Injection in Production

Prompt injection is the top security threat for AI in production. An attacker crafts input that overrides your system prompt, and your agent does something it shouldn't. Here's how to stop it.

What Prompt Injection Looks Like

Prompt injection comes in a few forms:

  • Direct injection — The user message contains instructions like "Ignore all previous instructions and..."
  • Indirect injection — Your agent fetches external data (web pages, emails) that contain hidden instructions
  • Jailbreak variants — Roleplay scenarios designed to bypass safety training

Why Traditional Defenses Fail

You might think a longer system prompt or a few examples will help. They won't. Here's why:

  • LLMs follow the most recent and prominent instructions, regardless of where they appear
  • There's no reliable way to mark input as "untrusted" in a standard API call
  • Input validation can't catch semantic attacks — the words look innocent out of context

What Actually Works

1. Input Screening

Run a lightweight classifier on every incoming message before it reaches your model. This catches the obvious attacks — direct injection attempts, known jailbreak patterns, and suspicious instruction-like language.

2. Output Guardrails

Check the model's response before returning it to the user. Look for:

  • Data leakage (PII, API keys, internal URLs)
  • Off-topic responses
  • Harmful content

This is your safety net for attacks that slip past input screening.

3. Separation of Concerns

Don't mix user input with system instructions in the same prompt context. Use separate message roles clearly and structure your prompts so that user content can't be confused with instructions.

4. Proxy-Level Enforcement

The most reliable approach is to enforce guardrails at the API proxy level. Every request and response passes through inspection before reaching your model or your user. DataHippo does this automatically — you set your policies once, and every call is screened.

Getting Started

Start with output guardrails (they're easiest to add) and work backward to input screening. If you're using DataHippo, both are built in. Define your policies in the dashboard and every call through the proxy is automatically protected.