trycourier/courier-mcp — agentic threat model
The Courier MCP server introduces significant risk of unauthorized message dissemination and data exfiltration if the orchestrating agent is compromised or manipulated via prompt injection. Its security posture is highly dependent on the protection of Courier API credentials and the guardrails of the calling LLM.
OWASP AIVSS score rationale
| Autonomy of Action | 0.60 | |
| Goal-Driven Planning | 0.20 | |
| Self-Modification | 0.00 | |
| Dynamic Tool Use | 0.50 | |
| Persistent Memory | 0.10 | |
| Contextual Awareness | 0.20 | |
| Dynamic Identity | 0.30 | |
| Multi-Agent Interactions | 0.20 | |
| Non-Determinism | 0.20 | |
| Opacity & Reflexivity | 0.20 |
Scored with the canonical OWASP AIVSS formula (AIVSS calculator reference); agentic risk factors estimated from the agent’s described capabilities.
MAESTRO 7-layer threat model
Per-layer threats for this agent. Layers tagged “not certain from listing” are general, caveated commentary where the public description didn’t pin that layer.
Not certain from the listing — The MCP server itself does not bundle a foundation model; it is designed to be called by external LLMs, making model-level threats dependent on the host client.
Not certain from the listing — While the tool interacts with recipient lists, the data operations, storage, and RAG pipelines are managed externally by Courier's platform or the host agent.
The server exposes powerful tools for sending messages and triggering automations. The primary threat is tool misuse, where prompt injection on the host LLM could force unauthorized notification dispatch or list manipulation.
Not certain from the listing — The hosting environment of the MCP server and the method of securing the Courier API credentials are not specified, leaving potential risks of credential theft or local privilege escalation.
Not certain from the listing — There is no mention of built-in guardrails, rate-limiting, or observability features to detect and block anomalous message-sending behavior or spam generation.
Security is heavily reliant on the Courier API credentials. Compromise of these credentials or lack of fine-grained access controls (RBAC) within the MCP configuration poses severe compliance and data privacy risks.
As an MCP tool, it integrates into multi-agent workflows where a compromised or rogue agent could abuse the notification capability to conduct phishing or social engineering attacks against external users.
MAESTRO — the 7-layer agentic threat-modeling framework (Cloud Security Alliance / Ken Huang).