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Scml

by ravindu57
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SCML — Securing Agentic AI at the Middleware Layer

Trust-aware context mediation for LLM agents, RAG pipelines, and tool-calling systems.

CI Tests Python TypeScript License

The Problem

  ┌─────────────────────────────────────────────────────────────────────┐
  │  LLM agents call tools, read documents, store memories.             │
  │  Every integration is a new attack surface.                         │
  │                                                                     │
  │  • Poisoned memory     → privilege escalation                       │
  │  • Malicious tool out  → agent hijacked, data exfiltrated           │
  │  • Prompt injection    → agent instructions overridden              │
  │                                                                     │
  │  Existing guardrails secure the MODEL.                              │
  │  SCML secures the MIDDLEWARE.                                       │
  └─────────────────────────────────────────────────────────────────────┘

LLM agents call external tools, read untrusted documents, and make decisions with real-world consequences. Every integration is a new attack surface. Existing guardrails focus on the model layer. SCML sits one layer lower — the middleware between the agent and the world — where policy is enforced before any tool call is authorised, before any memory write is persisted, and before any outbound response leaves the process.

Related MCP server: Agent Guardrail MCP

What SCML Does

SCML is a trust-aware context mediation middleware. Every data path passes through a pipeline that labels data, scans for injection, enforces declarative per-agent policy, redacts sensitive content, and logs every decision to a tamper-evident SHA-256 hash chain.

                          SCML Mediation Pipeline
  ┌──────────┐   ┌──────────┐   ┌──────────┐   ┌──────────┐   ┌──────────┐   ┌──────────┐
  │  Trust   │──▶│ Injection│──▶│  Policy  │──▶│  Memory  │──▶│  Output  │──▶│  Audit   │
  │  Label   │   │  Scan    │   │   Gate   │   │  Check   │   │  Redact  │   │   Log    │
  └──────────┘   └──────────┘   └──────────┘   └──────────┘   └──────────┘   └──────────┘
       │              │              │              │              │              │
       ▼              ▼              ▼              ▼              ▼              ▼
   Propagate      Detect &       Allow / Deny   Quarantine    Strip PII    SHA-256
    taint         block inject   per-agent       & score       & secrets    hash chain

Side-effect operations fail closed: an unreachable mediator denies by default, never permits by silence.

Multi-Tenant Policy Namespaces

One SCML instance can serve many companies, each with its own policy document. The tenant is bound to the API key, never supplied by the client:

Key format

Tenant

Principal

sk-abc123

default (TRUST_MEDIATOR_DEFAULT_TENANT)

fingerprint

alice:sk-abc123

default

alice

acme@sk-abc123

acme

fingerprint

acme@ops:sk-abc123

acme

ops

  • CallerDep derives the tenant from the authenticated key; no request model accepts a tenant_id field, so a caller cannot claim another company's namespace by shaping the body.

  • Policy reads, writes, per-agent updates, version history and rollback are all scoped to caller.tenant — Acme's agents and versions never collide with Globex's, even for the same agent_id.

  • A tenant that enrols no policy is deny-all (fail-closed at the tenant boundary); only the default tenant falls back to the gateway YAML.

  • Pre-tenancy deployments are unchanged: an unqualified key resolves to the default tenant, exactly as before.

Install

pip install trust-mediator            # client SDK — 14 packages, ~32 MB
pip install "trust-mediator[server]"  # run the mediator yourself

Python SDK

from scml import SCMLClient

scml = SCMLClient("http://localhost:8000", api_key="sk-...")

# Label and scan untrusted content
ctx = scml.mediate_context(session_id="s1", content=untrusted_document)

# Gate a tool call — untrusted arguments are denied, trusted ones pass
decision = scml.mediate_tool_call(
    session_id="s1",
    tool_name="send_email",
    arguments={"to": ctx.parsed["recipient"]},
    argument_trust_labels={"to": ctx.trust_label},
)
if not decision.allowed:
    raise RuntimeError(decision.reason)  # fail closed

TypeScript SDK (zero runtime deps)

const { SCML } = require('scml-client');
const scml = new SCML({ url: process.env.SCML_URL });

const ctx = await scml.mediateContext({ sessionId, content: untrustedDoc });
const d   = await scml.mediateToolCall({
  sessionId, tool: 'send_email',
  arguments: { to: ctx.parsed?.recipient },
  argumentTrustLabels: { to: ctx.trustLabel ?? 'untrusted_data' },
});
if (!d.allowed) throw new Error(d.reason);

MCP Server (Claude Desktop / Cursor / Windsurf)

MCP Server

SCML exposes its full security pipeline as MCP tools — any MCP-compatible client gets tool-call authorization, injection scanning, memory quarantine, and PII redaction with zero code changes.

  ┌──────────────┐       ┌──────────────┐       ┌──────────────┐
  │  LLM Client  │──────▶│  SCML MCP    │──────▶│  Your Tool   │
  │  (Claude,    │       │  Server      │       │  (API, DB,   │
  │   Cursor)    │◀──────│              │◀──────│   file, etc) │
  └──────────────┘       │  • authorize │       └──────────────┘
                         │  • scan      │
                         │  • quarantine│
                         │  • redact    │
                         └──────────────┘

Install

pip install trust-mediator mcp

Run

SCML_URL=http://localhost:8000 SCML_API_KEY=sk-your-key \
  python -m trust_mediator.mcp.server

Claude Desktop config

Add to ~/.claude/claude_desktop_config.json:

{
  "mcpServers": {
    "scml": {
      "command": "python",
      "args": ["-m", "trust_mediator.mcp.server"],
      "env": {
        "SCML_URL": "http://localhost:8000",
        "SCML_API_KEY": ""
      }
    }
  }
}

Available MCP tools

Tool

What it does

authorize_tool_call

Check if a tool call is allowed by policy

scan_content

Detect prompt injection in external content

check_memory_write

Score a memory write for integrity

redact_output

Strip PII and secrets from responses

get_audit_trail

Replay session decisions with hash chain

get_policy

Show active security policy

health_check

Verify SCML is running

Benchmarks

SCML is evaluated against four published attack corpora with 2,100+ attack cases. Every number is reproducible from a committed result file.

InjecAgent — 1,054 third-party cases (ACL Findings 2024)

Ablation truth: Removing the scanner → 0.0% ASR. Removing tool policy → 100.0% ASR. Tool policy is the entire defence. The scanner detects 0 of 1,054 attacks.

AgentDojo — All Four Suites (949 attacked cases)

Tool-Output Sanitizer — Closing the Slack Gap (FR-OR-03)

The slack gap (30.5% ASR) is caused by attacks delivered inside tool results that the model rewrites rather than copies. The deterministic ToolOutputSanitizer strips instruction framing before the agent reads them — no LLM call, no new dependencies.

105 attacked cases (21 tasks × 5 injections), 122 injected spans stripped, zero benign utility cost.

Memory Poisoning (48 in-house cases)

Pessimistic harm total: 18.8% (9/48). The 22 control-bypass cases are inert because the mediator never reads agent memory to decide authorisation.

Quick Start

git clone https://github.com/ravindu57/SCML.git && cd SCML
python3 -m venv .venv && .venv/bin/pip install -e ".[dev]"
DATABASE_URL="" REDIS_URL="" TRUST_MEDIATOR_API_KEYS="" \
  .venv/bin/uvicorn trust_mediator.api.app:app --port 8000 &
sleep 2
bash demo.sh                                        # run the demo
.venv/bin/pytest tests/ -q                           # 614 passed
cd clients/typescript && npm test                    # 25 passed

Interactive docs: http://localhost:8000/docs

Docker Compose

bash deploy.sh    # builds image, starts Postgres + Redis + mediator

Dashboard

bash run-demo.sh          # mediator :8000, dashboard :3100, agents :4000/:4100
bash run-demo.sh --stop   # tear down

Architecture

  ┌─────────────────────────────────────────────────────────────────────────┐
  │                        SCML System Architecture                         │
  ├─────────────────────────────────────────────────────────────────────────┤
  │                                                                         │
  │   ┌─────────────┐     ┌─────────────┐     ┌─────────────┐               │
  │   │   Python    │     │  TypeScript  │     │    gRPC     │              │
  │   │    SDK      │     │     SDK      │     │   Client    │              │
  │   └──────┬──────┘     └──────┬──────┘     └──────┬──────┘               │
  │          │                    │                    │                    │
  │          └────────────────────┼────────────────────┘                    │
  │                               │                                         │
  │                        ┌──────▼──────┐                                  │
  │                        │   FastAPI   │  /v1/mediate/*                   │
  │                        │   + gRPC    │  /v1/audit/*                     │
  │                        └──────┬──────┘                                  │
  │                               │                                         │
  │   ┌───────────────────────────▼───────────────────────────┐             │
  │   │              Mediation Pipeline                       │             │
  │   │                                                       │             │
  │   │  ┌────────┐ ┌────────┐ ┌────────┐ ┌────────┐          │             │
  │   │  │ Trust  │→│Inject. │→│ Policy │→│Memory  │          │             │
  │   │  │ Router │ │Scanner │ │ Engine │ │Integrity│         │             │
  │   │  └────────┘ └────────┘ └────────┘ └────────┘          │             │
  │   │       │                            │                  │             │
  │   │       └────────────┬───────────────┘                  │             │
  │   │                    ▼                                  │             │
  │   │            ┌──────────────┐     ┌──────────────┐      │             │
  │   │            │   Output     │     │    Audit     │      │             │
  │   │            │   Redactor   │     │    Logger    │      │             │
  │   │            └──────────────┘     └──────────────┘      │             │
  │   └───────────────────────────────────────────────────────┘             │
  │                               │                                         │
  │                    ┌──────────▼──────────┐                              │
  │                    │   PostgreSQL / SQLite│                             │
  │                    │   + Redis (optional) │                             │
  │                    └─────────────────────┘                              │
  └─────────────────────────────────────────────────────────────────────────┘

All config via TRUST_MEDIATOR_* env vars — nothing hardcoded. Every decision emits an AuditEvent.

API Surface

Production Deployment

Full integration guide: INTEGRATION.md — Python SDK, TypeScript SDK, LangChain guard, HTTP API, embedded mode, and examples for CrewAI, LangGraph, and OpenAI function calling.

Tests

DATABASE_URL="" TRUST_MEDIATOR_ENV=development REDIS_URL="" TRUST_MEDIATOR_API_KEYS="" \
  .venv/bin/pytest tests/ -q            # 614 passed

cd clients/typescript && npm test       # 25 passed

Apache License 2.0 — includes patent grant and defensive termination.

Tool Schema Changelog

Recent tool additions, removals, and schema changes observed during successful MCP inspections. Dates show when Glama detected each change.

No tool schema history has been recorded yet.

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