model-theft

A security check for APIs that serve predictions from a machine-learning model.

In plain words
What is it for?
It is for reviewing inference endpoints, model-serving deployments, access controls, rate limits, returned log probabilities or embedding vectors, and extraction monitoring.
Why use it?
It finds missing authentication, weak throttling, exposed model details, and missing monitoring that could let attackers copy or reconstruct a private model.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/thejefflarson/soundcheck/model-theft
Any agent
npx skills add thejefflarson/soundcheck --skill model-theft
Clone the repo
git clone --depth 1 https://github.com/thejefflarson/soundcheck

Made for: Claude Code, Codex.

Per session 47 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 676 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00047 $0.00676
Opus 5 $0.00023 $0.00338
Sonnet 5 $0.00009 $0.00135
Haiku 4.5 $0.00005 $0.00068

Measured 2d ago against content hash d2009f33653d, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

model-theft scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude/skills/model-theft/SKILL.md · 61 lines

How it starts

The opening of the file, as written. The whole thing — 61 lines — stays where its author put it; the contents beside it link to each section on GitHub.

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.

Read the full file on GitHub · 61 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 61 lines · 47 tokens per session scan A d2009f33653d

Subscribe to this mod's changes

model-theft is a skill published in the GitHub repository thejefflarson/soundcheck (20 stars, last pushed 1mo ago), licensed MIT. It adds 47 tokens to every session and 676 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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