Model Theft

---
name: model-theft
description: Detects inference endpoints without authentication or throttling, allowing
  model weight reconstruction. Use when writing inference API endpoints,
  deploying LLM-serving infrastructure, implementing model access controls, or
  configuring rate limiting and authentication for model endpoints.
---

# Model Theft (OWASP LLM10:2025)

## What this checks

Prevents unauthorized replication of proprietary models through API abuse. Unauthenticated
or unthrottled inference endpoints let attackers systematically query a model to
reconstruct its weights or distill a clone — stealing the commercial and IP value
of the deployment.

## Vulnerable patterns

- Inference endpoint has no authentication — any client can query freely
- Rate limiting applied per IP only, trivially bypassed with rotating proxies
- Response includes raw `logprobs` or full embedding vectors, enabling extraction
- No monitoring for systematic/grid-search query patterns that signal extraction attempts

## Fix immediately

Flag the vulnerable code and explain the risk. Then suggest a fix that establishes
these properties:

1. **Every inference endpoint requires authentication** — API key, bearer token,
   or mTLS. Unauthenticated endpoints are free training data for anyone who wants
   to clone the model.
2. **Rate limits are keyed on the authenticated principal, not the IP.** IP-only
   throttles are defeated by rotating proxies and residential IP pools; a
   per-user or per-key quota follows the attacker even as IPs churn.
3. **Extraction-signal fields are stripped from responses.** Log-probabilities,
   full embedding vectors, and per-token probabilities are the primary signals
   distillation attacks use to reconstruct a model. If a caller does not strictly
   need them, do not return them.
4. **Query patterns are monitored for extraction signatures** — high-volume,
   low-entropy, systematic grid-search probes. Alerts fire on anomalies; the
   handler records user identity, timestamp, and prompt (or a content
   fingerprint) for after-the-fact investigation.

Translate each principle to the serving framework, auth provider, and rate-limiter
of the audited file. Use the framework's documented authentication and throttling
middleware — do not roll your own.

## Verification

- [ ] Every inference endpoint requires a valid API key or bearer token
- [ ] Rate limits are enforced per authenticated user, not per IP address
- [ ] Log-probabilities, raw embeddings, and weight data are excluded from API responses
- [ ] Query logs include user identity, timestamp, and either the prompt itself or a stable fingerprint (hash, embedding, or normalized form) sufficient to detect content-pattern anomalies. Logging only metadata (length, token count, request id) without any reconstructable prompt signal does not satisfy this. Choice between raw prompt and fingerprint is a privacy tradeoff — document the decision.

## References

- CWE-285 ([Improper Authorization](https://cwe.mitre.org/data/definitions/285.html))
- CWE-307 ([Improper Restriction of Excessive Authentication Attempts](https://cwe.mitre.org/data/definitions/307.html))
- [OWASP LLM10:2025 Model Theft](https://genai.owasp.org/llmrisk/llm10-model-theft/)