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§ I · Domain MAS · Control 9 of 9
Control
MAS-09
Edition
v.1.3
Status
Public review

MAS · Multi-Agent Systems

MAS-09External agent trust boundaries

Where the agent invokes external third-party agents (including via agent-to-agent protocols, agent marketplaces, or partner platforms), the integration is treated as a third-party dependency with documented risk assessment, contractual data-use commitments, and trust-boundary handling.

Where the agent invokes external third-party agents, including via agent-to-agent protocols, agent marketplaces, or partner platforms, the integration is treated as a third-party dependency under OUT-06 and OUT-09, with documented risk assessment, contractual data-use commitments, and trust-boundary handling under INP-02. External agents are never trusted by default.

Table MAS-09.1 · Maturity criteria · v.1.3

L1 to L5 · the lowest level in scope caps the agent
L1Ad hoc

Controls exist informally; documentation is incomplete; no consistent review.

L2Documented

Controls are written down; ownership is assigned; review cadence is defined.

L3Operated

Controls are followed in practice; evidence is collected; deviations are tracked.

All external agent integrations are documented in the third-party integration inventory; risk assessments are current; contractual terms address data use and trust boundaries; the integration is tested as part of adversarial assessment.

L4Measured

Control effectiveness is measured against documented thresholds; trends are reported.

L5Continuously Improved

Controls evolve based on incident learning; maturity gains are evidenced over time.

The v1.3 edition publishes a control-specific criterion at L3 (Operated). The other levels apply the general ladder to this control; see the maturity ladder.

Evidence an assessor asks for

  1. E.1

    All external agent integrations are documented in the third-party integration inventory.

  2. E.2

    Risk assessments are current.

  3. E.3

    Contractual terms address data use and trust boundaries.

  4. E.4

    The integration is tested as part of adversarial assessment.

Table MAS-09.2 · Framework mappings

6 of 7 frameworks carry a control-level reference
NIST AI RMFGOVERN 6.1, MANAGE 3.1NIST AI Risk Management Framework 1.0
ISO/IEC 42001·ISO/IEC 42001:2023 · Artificial intelligence management system
OWASP LLM Top 10LLM06OWASP Top 10 for Large Language Model Applications
SOC 2 (TSC)CC9.2AICPA Trust Services Criteria for SOC 2 Type II
EU AI ActArt. 25(1)EU AI Act · Regulation (EU) 2024/1689
MITRE ATLASLateral MovementMITRE ATLAS · Adversarial Threat Landscape for AI Systems
SingaporeMAIGF AccountabilitySingapore Model AI Governance Framework / AI Verify / PDPA

Mappings are directional: meeting this control evidences but does not by itself satisfy the external requirement. A middle dot means no control-level reference is published at this edition; see the crosswalk.

Related controls and terms

Cite this control

Human Intelligence. HI-AAF v1.3, MAS-09 External agent trust boundaries. Public review edition, July 2026. https://humanintel.net/standard/mas/mas-09

Edition v.1.3 · July 2026 · Public review · Markdown · PDF

https://humanintel.net/standard/mas/mas-09

Notice

HI-AAF v1.3 is an independent framework published by Human Intelligence. It is not affiliated with NIST, ISO, AICPA, or any government or accreditation body. The framework is offered openly for review during the current draft cycle.