Capability Model

The formal statement within a Plugin Manifest where a plugin enumerates the specific permissions it requires to function. This is a proactive request, not a runtime discovery.

• Declarations are typically a list of strings (e.g., ["read_files", "network_access", "execute_shell"]).
• Each capability should be atomic and specific (e.g., "write_to_logs" is better than a broad "system_access").
• The declaration forms the basis for the policy evaluation performed by the host system.

The host system's logic that evaluates a plugin's capability requests against a set of security policies and the execution context. It is the decision-making core of the model.

• Policies can be static (defined in configuration files) or dynamic (based on user role, environment, or data sensitivity).
• The engine performs a grant/deny evaluation, potentially with partial grants (e.g., allowing read_files but only for a specific directory).
• It implements the principle of least privilege, granting only the minimum capabilities necessary.

The system hooks and guards that actively prevent a plugin from performing actions for which it lacks a granted capability. This transforms policy decisions into enforced reality.

• This layer intercepts all sensitive operations (file I/O, network calls, process execution).
• It checks the calling plugin's granted capability set before allowing the operation to proceed.
• Enforcement is often implemented via operating system-level sandboxing (e.g., seccomp-bpf, AppArmor) or language-level guards.

The runtime object or data structure that represents the granted permissions for a specific plugin instance during a session. It is the proof of authorization.

• This is often an opaque token or a context object passed to the plugin or held by the host.
• The token is immutable for the session's duration and is validated by the Runtime Enforcement Layer.
• It may contain scoped parameters (e.g., network_access is granted but only for the domain api.internal.example.com).

An immutable record of all capability-related events, crucial for security, compliance, and debugging. It provides a verifiable history of the Principle of Least Privilege in action.

• Logs capture: Capability requests, policy decisions (grant/deny with rationale), and enforcement actions (blocked operations).
• Entries are tamper-evident and include timestamps, plugin identity, and user/agent context.
• This log is essential for post-incident analysis and demonstrating compliance with frameworks like NIST SP 800-53 or SOC 2.

A Capability Model is the policy framework that defines what a plugin can do, while sandboxing provides the technical isolation that enforces how it is contained. They are complementary concepts.

• Sandboxing (e.g., gVisor, WebAssembly) creates the isolated execution environment.
• The Capability Model defines the allowed interactions between that sandbox and the host system or network.
• Together, they implement defense-in-depth: even if a plugin is compromised, the capability model limits its potential impact.

A metadata file (JSON/YAML) that declares a plugin's identity, version, dependencies, and the specific capabilities it requires from the host system. It is the primary document a capability model evaluates to grant or deny permissions.

• Key Fields: id, version, name, required_capabilities, schema.
• Example: A file editor plugin's manifest might declare required_capabilities: ["read_files", "write_files"] and specify the file path patterns it can access.

A security mechanism that creates an isolated execution environment for a plugin, enforcing the capabilities granted by the policy. It restricts access to system resources like the filesystem, network, or other processes.

• Implementation: Uses OS-level containers, virtual machines, or language runtimes (e.g., WebAssembly).
• Relation to Capability Model: The model's policy decisions define the sandbox's boundaries. A plugin denied the network_access capability runs in a sandbox with no network interfaces.

The system that defines and enforces what tools, data, and actions an AI agent or plugin is authorized to access. A capability model is a specific implementation of this system.

• Key Concepts: Principle of Least Privilege, role-based access control (RBAC), attribute-based access control (ABAC).
• Scopes: Granular permissions beyond binary grants, e.g., read_files:/var/log/ vs. read_files:/home/user/.

A formal specification (Interface Definition Language, OpenAPI schema) that defines the methods, data types, and behaviors for interaction between components. In a capability model, the host's plugin API is a contract.

• Purpose: Guarantees stability and enables independent plugin development.
• Capability Binding: The contract defines which API endpoints or functions are gated behind specific capabilities (e.g., callExternalAPI requires network_access).

The isolation of execution within a hardened, tamper-resistant environment. For AI agents using plugins, this provides an extra layer of security for sensitive tool execution, complementing capability-based authorization.

• Use Case: Executing a plugin that handles cryptographic keys or regulated data.
• Technology: Hardware-based (e.g., Intel SGX, AMD SEV) or advanced software sandboxing.

A design principle where the framework (plugin host) manages the lifecycle and coordination of components (plugins). Plugins respond to events or calls from the host, which retains control.

• Relation to Capability Model: The host uses IoC to inject only the authorized capabilities into a plugin during its initialization. The plugin cannot acquire capabilities on its own; it must request them and have them granted by the host's IoC container.