llm-security-commons

Runtime-neutral core for LLM and agent security detection: detector data, normative contracts and a conformance corpus that several runtimes can share.

Detection logic gets reimplemented every time it crosses a language boundary, and the copies drift: the Node scanner flags a zero-width carrier the Python guard misses, and nobody notices until an incident. This repository holds the part that should never have been copied — the pattern tables, the code-point carriers, the calibration thresholds, the finding contract, and a fixture corpus with expected verdicts — so that two independent implementations can be held to the same answer on the same input.

It is for anyone building or maintaining a detector for prompt injection, secret egress, unicode-carrier smuggling or active content in untrusted text, on any runtime.

It holds no runnable code. Data, specifications and fixtures only.

Install

Nothing to install — this repository is vendored into consumers, not installed.

As a git subtree (recommended: history is preserved and upgrades are a single command):

git subtree add --prefix vendor/commons \
  https://git.fromaitochitta.com/open/llm-security-commons.git v0.1.0 --squash

# later, to move to a newer tag
git subtree pull --prefix vendor/commons \
  https://git.fromaitochitta.com/open/llm-security-commons.git v0.2.0 --squash

Or pin a tag and copy — fork-and-own is an explicitly supported path:

git clone --depth 1 --branch v0.1.0 \
  https://git.fromaitochitta.com/open/llm-security-commons.git

Always vendor a tag, never main. The tag is what a conformance result can be attributed to.

Requirements

A JSON parser and the ability to read a text file. That is the entire dependency surface, and keeping it that small is the point.

What it does

Path	Contents
lexicon/injection-lexicon.json	Prompt-injection pattern lexicon: instruction-override, exfiltration and role-confusion families with per-pattern ids.
codepoints/carriers.json	Invisible and deceptive carriers: zero-width characters, BIDI controls, Unicode Tag block ranges, and the homoglyph map.
signatures/secret-egress.json	Credential and token shapes that must never leave a machine, in a portable regex dialect.
signatures/malware-signatures.json	Signature set for the malicious-code class (SIG).
signatures/active-content.json	Active content that renders or fetches on its own — Markdown images, links, reference definitions and autolinks, data: URIs, active HTML. The EchoLeak class.
calibration/calibration.json	The numbers a detector must not invent: entropy floors, scan caps, disposition ranks.
mapping/owasp-map.json	Finding-id prefix → OWASP taxonomy entry (LLM / ASI / AST / MCP).
schema/finding.schema.json	Normative. The finding contract, plus the SARIF and JSONL output profiles.
spec/decode-pipeline.md	Normative. The decode order, in RFC 2119 language. Two runtimes that decode in different orders will disagree on identical input; this is the file that stops that.
conformance/	One directory per case: input.txt in, expected.json out. Ground truth.
docs/extraction-plan.md	Informative: where each file was seeded from, and what v0.1.0 promised.

Every JSON file carries a top-level version. Every normative specification carries a Status: normative marker.

How a consumer proves it conforms

Run every conformance/<case>/input.txt through your detector, serialize the result per schema/finding.schema.json, and compare to expected.json. Disagreement means your runtime is wrong, or the fixture is — and the fixture only changes in its own commit, with the reason written down.

There is no CI in this organisation and nothing runs that comparison automatically. It runs in each consumer's own test suite, against a pinned tag.

Non-goals

• Not a scanner. There is no engine here, and there will not be one. If you are looking for something to run, you want a consumer — llm-security for Claude Code.
• Not a framework or a library. No package manifest, no dependencies, no build.
• Not a general-purpose Unicode or regex toolkit. The tables cover what the detection classes need, not the standard.
• Not a vulnerability feed. No CVEs, no advisories, nothing time-sensitive. Everything here is offline and deterministic.
• Not a policy engine. calibration.json publishes the thresholds; deciding what to do when one is crossed belongs to the consumer.
• Not the place to fix a consumer's behaviour. Data extracted from an implementation is kept behaviour-identical on purpose. A disagreement is reported to that implementation and decided there, where it is tested.

Known limitations

• Coverage is the union of what the seed implementations detected, not of what exists. A class absent from conformance/ has not been shown to work anywhere.
• Regex portability is a real risk. Pattern data is written for a common subset, but engines differ (lookbehind, named groups, Unicode property escapes). A consumer whose engine rejects a pattern must report it rather than silently skip it — a skipped pattern is an invisible false negative.
• Fixtures prove agreement, not correctness. Two runtimes passing the same corpus agree with each other and with the fixture author. A wrong expected.json makes both wrong identically.
• The homoglyph map is finite. Confusable coverage is a long tail; absence from the map is not evidence a character is safe.

Changelog

See CHANGELOG.md.

License

MIT — see LICENSE. Fork-and-own is an intended use, not a tolerated one.