Agent Tool and Permission Design Template (OWASP ASI02, ASI03)

Agent tool permissions: tool inventory, capability classes, least agency, non-human identity, approval tiers, sandboxing, limits, audit, revocation, tests

AI・データフルOWASP Top 10 for Agentic Applications 2026 (ASI02, ASI03); OWASP Top 10 for LLM Applications 2026 (LLM03 Excessive Agency)CC BY-SA 4.0agent tool permission design更新 2026/10/21

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使い方: Use it before granting an AI agent any tool with side effects, or when reviewing an agent's access. Fill the tool inventory and capability classification first, then derive approval tiers, credential lifetimes and policy rules from the class. The main pitfall is enforcing limits in the prompt instead of in the runtime, or giving the agent one long-lived broad credential.

プレビュー

Agent Tool and Permission Design: [Agent or system name]

Design document for the tools an AI agent can call and the permissions behind them: tool inventory, capability classification, the least-agency principle, non-human identity and credential scoping, approval tiers and step-up confirmation, sandboxing, rate and spend limits, validation of tool-call inputs and outputs, audit logging, revocation and a test plan. Threats are mapped to the OWASP Top 10 for Agentic Applications 2026 (ASI02 Tool Misuse and Exploitation, ASI03 Identity and Privilege Abuse, and related entries) and to Excessive Agency in the OWASP Top 10 for LLM Applications 2026 (LLM03:2026, as numbered in the August 2026 edition; it was LLM06 in 2025). Replace every [bracketed] value and every row marked Example. Worked examples use an IT service desk agent that reads tickets, resets passwords and opens change requests.

Document control

Field	Value
Document ID	[ATP-DES-001]
Agent or system	[Name] [v1.0.0]
Tool set version	[v1.0]
Version	[0.1]
Status	[Draft / In review / Approved / Retired]
Owner	[@agent-owner]
Approvers/reviewers	[@security-engineer], [@identity-team], [@business-owner]
Identity provider	[Name of IdP or workload identity system]
Policy engine	[Example: Open Policy Agent / Cedar / in-house]
Classification	[Internal / Confidential]
Last updated	YYYY-MM-DD
Related documents	[Agent specification], [MCP server specifications], [Agentic threat model], [Runbook]

Approvals

Role	Name	Decision	Date
Agent owner	[@name]	[Approve / Approve with conditions / Reject]	YYYY-MM-DD
Security	[@name]	[Decision]	YYYY-MM-DD
Identity and access management	[@name]	[Decision]	YYYY-MM-DD
Owner of each target system	[@name]	[Decision]	YYYY-MM-DD

Revision history

Version	Date	Author	Change summary
0.1	YYYY-MM-DD	[@name]	First draft
1.0	YYYY-MM-DD	[@name]	Example: Approved with five tools, password reset at tier T2
1.1	YYYY-MM-DD	[@name]	Example: `create_change_request` added at tier T3 after pilot

Scope and context
Design principles
Tool inventory
Capability classification
Non-human identity and credentials
Authorization policy
Approval tiers and step-up confirmation
Sandboxing and isolation
Rate, volume and spend limits
Tool-call validation
Audit logging
Revocation and emergency controls
Threat mapping
Test plan
Traceability matrix
Glossary and references

1. Scope and context

Item	Value
Agent purpose	Example: Resolve routine service desk tickets for employees
Acts on behalf of	Example: The employee who opened the ticket (delegated), plus the service desk as an organisation
Target systems	Example: Ticketing system, identity provider, change management system
Systems explicitly out of reach	Example: HR records, payroll, production servers, email sending
Autonomy level	Example: Level 2: low-risk actions alone, high-risk actions approved by a human
Users	Example: About 4,000 employees, 25 service desk analysts

2. Design principles

ID	Principle	What it means here
ATP-P-001	Least agency	Give the agent only the tools, autonomy and reach the task needs; remove anything unused for [30] days
ATP-P-002	Least privilege	Each tool runs with the narrowest scope that still works; no wildcard scopes
ATP-P-003	Deny by default	A tool call is refused unless a policy rule allows it
ATP-P-004	Separate identity	The agent has its own non-human identity; it never reuses a human's session or a shared service account
ATP-P-005	Credentials outside the model	Tokens and keys never enter prompts, context or tool results
ATP-P-006	Human control over irreversible effects	Irreversible or external actions need human approval or are not offered
ATP-P-007	Enforce outside the model	Limits and checks run in the tool runtime or policy engine
ATP-P-008	Everything logged	Every tool call, decision and approval is recorded with its principal

3. Tool inventory

ID	Tool	Provided by	Purpose	Target system	Class (section 4)	Tier (section 7)
ATP-TOOL-001 (Example)	`get_ticket`	Internal MCP server `itsm-mcp`	Read ticket and history	Ticketing	C1	T0
ATP-TOOL-002 (Example)	`search_kb`	Internal MCP server `kb-mcp`	Search knowledge base	Knowledge base	C1	T0
ATP-TOOL-003 (Example)	`add_ticket_comment`	`itsm-mcp`	Reply on the ticket	Ticketing	C3	T1
ATP-TOOL-004 (Example)	`reset_password`	`idp-mcp`	Trigger a self-service reset link to the requester	Identity provider	C4	T2
ATP-TOOL-005 (Example)	`create_change_request`	`itsm-mcp`	Open a change for a human team	Change management	C3	T3

3.1 Removed or rejected tools

Tool	Reason not granted
Example: `set_password`	Agent would know the new password; reset link achieves the goal
Example: `run_shell`	No task requires code execution
Example: `send_email`	Replies go through the ticket only

3.2 Tool definition requirements

Each tool must have: a name and description written for the model, including when not to use it; a strict input schema with additionalProperties: false; an output schema; the side effects stated plainly; and, for MCP tools, every annotation hint set explicitly.

{
  "name": "reset_password",
  "title": "Send password reset link",
  "description": "Send a self-service password reset link to the employee who opened the ticket. Use only when the ticket requester asks for their own reset and identity has been verified. Never use for another person or for privileged accounts.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "ticket_id": {"type": "string", "pattern": "^INC[0-9]{7}$"},
      "verification_ref": {"type": "string", "pattern": "^VER-[A-Z0-9]{10}$"}
    },
    "required": ["ticket_id", "verification_ref"],
    "additionalProperties": false
  },
  "annotations": {"readOnlyHint": false, "destructiveHint": false, "idempotentHint": true, "openWorldHint": false}
}

The target account is not an argument: the runtime derives it from the ticket requester, so the model cannot choose whose password is reset.

4. Capability classification

Class	Name	Definition	Examples	Default tier
C0	No side effect, local	Computation with no data access	Example: Date arithmetic, formatting	T0
C1	Read, internal	Reads internal data within the principal's rights	Example: `get_ticket`, `search_kb`	T0
C2	Read, open world	Reads untrusted external content	Example: Web fetch	T0 with content treated as untrusted
C3	Write, reversible	Changes internal state that can be undone	Example: Ticket comment, draft change request	T1 or T3
C4	Write, sensitive or hard to reverse	Security, identity, financial or bulk changes	Example: Password reset, access grant	T2 or higher
C5	Irreversible or external effect	Cannot be undone, or reaches people or systems outside the organisation	Example: Payment, external email, deletion without backup	T4 or not offered

4.1 Classification record

Tool	Reads	Writes	Reversible?	External effect?	Data sensitivity	Class
ATP-TOOL-003 (Example)	Ticket	Comment	Yes, by analyst edit	Visible to requester (internal)	Internal	C3
ATP-TOOL-004 (Example)	Account status	Reset token issued	Partly: old password invalidated	Message to requester	Confidential	C4
ATP-TOOL-005 (Example)	Ticket	New change record	Yes, change can be cancelled	None	Internal	C3

5. Non-human identity and credentials

5.1 Identities

ID	Identity	Type	Used for	Owner	Review cycle
ATP-ID-001 (Example)	`agent-servicedesk-prod`	Workload identity (federated, no static secret)	Calling MCP servers	[@agent-owner]	Quarterly
ATP-ID-002 (Example)	`itsm-mcp` service principal	Service account	Ticketing API calls	[@itsm-team]	Quarterly
ATP-ID-003 (Example)	`idp-mcp` service principal	Service account with reset-only role	Identity provider reset API	[@identity-team]	Monthly

5.2 Delegation model

[Describe how the agent acts for a user.] Example: The agent receives a token for the requester through OAuth 2.0 Token Exchange (RFC 8693) with the agent as actor, so downstream systems see both the user and the agent. Each token is audience-restricted to one MCP server (RFC 8707 resource indicator). MCP servers do not pass user tokens through to backends; they call backends with their own service principals and record the user and agent identity in audit fields.

5.3 Credential register

Credential	Holder	Scope	Lifetime	Storage	Rotation
Example: Agent access token for `itsm-mcp`	Agent runtime	`tickets:read tickets:comment changes:create`	10 minutes	Memory only	Per request
Example: Agent access token for `idp-mcp`	Agent runtime	`password:reset-link`	5 minutes, issued only after T2 approval	Memory only	Per action
Example: `itsm-mcp` backend credential	MCP server	Ticketing API role "agent-writer"	1 hour	Secret manager	Automatic

Rules:

[Example: No credential is ever placed in the model context, a tool result or a log line.]
[Example: Credentials for C4 and C5 tools are minted just in time, after approval, for one call.]
[Example: Staging and production identities are separate; staging tokens are rejected by production servers.]

6. Authorization policy

ID	Rule	Inputs to the decision	Effect
ATP-POL-001 (Example)	Only tools in section 3 are callable	Tool name	Deny others
ATP-POL-002 (Example)	`reset_password` only for the ticket requester's own account	Ticket requester, derived target	Deny if they differ
ATP-POL-003 (Example)	`reset_password` never for accounts in privileged groups	Group membership	Deny and escalate
ATP-POL-004 (Example)	Comments may not contain links outside approved domains	Comment body	Deny with reason
ATP-POL-005 (Example)	No write tool after content from a C2 tool entered the context in the same turn, unless approved	Context provenance flags	Require T2 approval
ATP-POL-006 (Example)	Calls outside business hours limited to C0 and C1	Time	Deny writes

permit(agent, "reset_password", args) when
  call.derived_target == ticket(args.ticket_id).requester
  and not in_group(call.derived_target, "privileged")
  and approval(args.ticket_id, "T2").granted
  and approval.age_seconds < 300

The block above is pseudo-code; call.derived_target is the account the runtime resolved from the ticket, never a model-supplied value. Write the real rule in your policy engine's language and keep it under version control with tests.

7. Approval tiers and step-up confirmation

Tier	Name	Who approves	How	Expiry
T0	Automatic	Nobody, policy only	Logged	n/a
T1	Notify	Nobody before; analyst can undo	Notification with undo link	Undo window [24 h]
T2	User confirmation	The requesting user	Step-up: re-authenticate with MFA and confirm the exact action	[5 min]
T3	Operator approval	A service desk analyst	Approve or reject in the console	[4 h], then returned to queue
T4	Dual approval	Two people, one from the system owner team	Separate approvals	[24 h]
Not offered	n/a	n/a	Tool not granted	n/a

7.1 Assignment

Tool or condition	Tier	Reason
ATP-TOOL-001, ATP-TOOL-002 (Example)	T0	Read only, within the requester's rights
ATP-TOOL-003 (Example)	T1	Reversible, internal
ATP-TOOL-004 (Example)	T2	Security-sensitive; the user proves they asked for it
ATP-TOOL-005 (Example)	T3	Starts work for another team
Any write after C2 content in context (Example)	T2 at least	Possible injected instruction

7.2 Approval screen content

The approver must see: the tool name in plain words, every argument with its real value, the target resource, the class and whether it can be undone, the reason the agent gives, and the source of any content that led to the call. The approve button is not the default focus, and approving does not also approve later calls.

8. Sandboxing and isolation

Aspect	Design
Agent runtime	Example: Container per run, read-only root file system, no shell
Network egress	Example: Allow-list: the three MCP servers and the model provider only
File system	Example: Per-run scratch directory, wiped at end of run
Code execution	Example: Not offered (no C5 code tools)
Browsing or fetching	Example: Not offered in this agent; if added, run in a separate worker with no write tools
Secrets	Example: Workload identity only; no secrets mounted in the agent container
Tenant isolation	Example: One tenant per run; tool calls carry the tenant and servers check it

9. Rate, volume and spend limits

ID	Limit	Scope	Value	On breach
ATP-LIM-001 (Example)	Tool calls	Per run	20	Run stops, ticket escalated
ATP-LIM-002 (Example)	`reset_password`	Per requester per day	2	Deny, escalate to analyst
ATP-LIM-003 (Example)	`reset_password`	System-wide per hour	30	Deny new resets, page on-call
ATP-LIM-004 (Example)	Comments	Per ticket per hour	3	Deny, notify analyst
ATP-LIM-005 (Example)	Change requests	Per day	10	Queue for analyst
ATP-LIM-006 (Example)	Model spend	Per day	[Amount]	Pause agent
ATP-LIM-007 (Example)	Identical call repeated	Per run	2	Deny third attempt

10. Tool-call validation

10.1 Input checks

Check	Rule
Schema	Strict JSON Schema; unknown fields rejected
Types and ranges	Patterns, enumerations, length limits on every string
Resource ownership	Target resource belongs to the principal and tenant
Derived arguments	Sensitive targets (account, amount, recipient) derived by the runtime where possible
Injection in arguments	Free-text fields scanned for markup, links and command syntax before use in downstream systems
Idempotency	Write calls carry an idempotency key from the run and step

10.2 Output checks

Check	Rule
Schema	Result matches the output schema; otherwise an error is returned to the model
Size	Truncated to [8,000] characters with a note
Secrets and personal data	Masked by pattern before entering context
Untrusted content marking	Text from tickets, documents or external sources is labelled as data
Errors	Actionable message without stack traces, hostnames or credentials

11. Audit logging

Field	Content
Time and run ID	UTC timestamp, run ID, trace ID
Principals	Human on whose behalf, agent identity, MCP server identity
Tool and arguments	Tool name, arguments with sensitive values hashed or masked
Policy decision	Rule IDs evaluated, result, reason
Approval	Tier, approver, time, what was shown
Result	Outcome, error code, resource IDs changed
Provenance	Whether untrusted content was in context when the call was planned

Retention: [Example: 1 year for T0 and T1 calls, 7 years for T2 and above]. Storage: [Example: append-only log store; the agent identity has no read or delete rights on it].

12. Revocation and emergency controls

ID	Control	Effect	Who can trigger	Target time
ATP-REV-001 (Example)	Disable one tool	Policy denies the tool for all runs	Agent owner, security	1 min
ATP-REV-002 (Example)	Revoke agent identity	Workload identity disabled; tokens refused	Identity team, security	5 min
ATP-REV-003 (Example)	Stop all runs	Runtime halts in-flight runs at the next step	Owner, on-call	30 s
ATP-REV-004 (Example)	Rotate MCP server backend credentials	Backend sessions invalidated	Server owner	15 min
ATP-REV-005 (Example)	Reverse actions	Runbook lists how to undo each C3 and C4 action	Analyst	Per runbook

Access reviews: [Example: quarterly review of identities and scopes against section 3; any tool unused for 30 days is removed.]

13. Threat mapping

Source and ID	Risk	Scenario here	Controls	Residual
ASI02	Tool Misuse and Exploitation	Example: Ticket text persuades the agent to post a phishing link as a comment	ATP-POL-004, 10.1, T1 undo	Low
ASI03	Identity and Privilege Abuse	Example: Agent resets the password of a manager named in the ticket	ATP-POL-002, derived target, T2	Low
ASI03	Identity and Privilege Abuse	Example: Stolen long-lived token reused outside the agent	Short-lived audience-bound tokens (5.3)	Low
ASI01	Agent Goal Hijack	Example: Knowledge base article contains instructions to open many changes	ATP-POL-005, ATP-LIM-005	Low
ASI05	Unexpected Code Execution (RCE)	Example: Not applicable: no code execution tools	Section 8	Not applicable
ASI09	Human-Agent Trust Exploitation	Example: Approval screen shows a misleading summary	7.2 shows real arguments	Medium
ASI10	Rogue Agents	Example: Agent repeats resets in a loop after a model change	ATP-LIM-002, ATP-LIM-003, ATP-REV-003	Low
LLM03:2026	Excessive Agency	Example: Tool set includes `set_password` with admin scope	Section 3.1 removal, ATP-P-001	Low
LLM01:2026	Prompt Injection	Example: Instructions in an attached file	10.2 marking, ATP-POL-005	Medium

ASI identifiers follow the OWASP Top 10 for Agentic Applications for 2026. LLM identifiers follow the OWASP Top 10 for LLM Applications 2026 as numbered when this template was written; check the current list at genai.owasp.org before an assurance review.

14. Test plan

ID	Test	Method	Expected result	Linked control
ATP-TST-001 (Example)	Call a tool not in the inventory	Direct runtime call	Denied, logged	ATP-POL-001
ATP-TST-002 (Example)	Reset another user's password via ticket text	Adversarial ticket	Denied, escalated	ATP-POL-002
ATP-TST-003 (Example)	Reset a privileged account	Fixture account	Denied	ATP-POL-003
ATP-TST-004 (Example)	Approve a T2 action after 6 minutes	Delayed approval	Expired, new approval needed	Section 7
ATP-TST-005 (Example)	31 resets in an hour	Load script	Thirty-first denied, page sent	ATP-LIM-003
ATP-TST-006 (Example)	Token reuse from outside the runtime	Replay captured token	Rejected (audience or expiry)	5.3
ATP-TST-007 (Example)	Secret pattern in a tool result	Fixture result	Masked before context	10.2
ATP-TST-008 (Example)	Disable a tool during a run	Toggle ATP-REV-001	Next call denied	ATP-REV-001
ATP-TST-009 (Example)	Revoke agent identity	Toggle ATP-REV-002	All calls fail within 5 min	ATP-REV-002
ATP-TST-010 (Example)	Audit completeness	Compare runs with log	Every call has a complete entry	Section 11

15. Traceability matrix

Tool	Class	Tier	Identity	Policy	Limits	Tests
ATP-TOOL-001 (Example)	C1	T0	ATP-ID-001, ATP-ID-002	ATP-POL-001	ATP-LIM-001	ATP-TST-001
ATP-TOOL-003 (Example)	C3	T1	ATP-ID-001, ATP-ID-002	ATP-POL-004	ATP-LIM-004	ATP-TST-007
ATP-TOOL-004 (Example)	C4	T2	ATP-ID-001, ATP-ID-003	ATP-POL-002, ATP-POL-003, ATP-POL-005	ATP-LIM-002, ATP-LIM-003	ATP-TST-002 to ATP-TST-006
ATP-TOOL-005 (Example)	C3	T3	ATP-ID-001, ATP-ID-002	ATP-POL-001	ATP-LIM-005	ATP-TST-010

16. Glossary and references

Term	Meaning
Least agency	Granting an agent only the autonomy, tools and reach its task requires
Non-human identity	An identity for software (agent, service, workload) rather than a person
Step-up confirmation	A stronger check, such as re-authentication, before a sensitive action
Token exchange	Issuing a new token that represents a user and an acting agent together
Audience restriction	Binding a token to one resource server so it is refused elsewhere
Open-world tool	A tool that reads or affects systems outside the organisation's control

References:

OWASP Top 10 for Agentic Applications for 2026, December 2025, https://genai.owasp.org/resource/owasp-top-10-for-agentic-applications-for-2026/
OWASP Top 10 for LLM Applications 2026, August 2026, https://genai.owasp.org/resource/owasp-genai-llm-top-10-2026/
Model Context Protocol specification, revision 2026-07-28, https://modelcontextprotocol.io/specification/2026-07-28
RFC 8693 OAuth 2.0 Token Exchange; RFC 8707 Resource Indicators for OAuth 2.0
[Internal identity and access management standard]

Standard and licence note

Based on the OWASP Top 10 for Agentic Applications for 2026 and the OWASP Top 10 for LLM Applications 2026 by the OWASP GenAI Security Project (https://genai.owasp.org/), licensed under Creative Commons Attribution-ShareAlike 4.0 (https://creativecommons.org/licenses/by-sa/4.0/). Entry IDs and short names are used for mapping and all descriptions are original text. Because section 13 adapts those lists, the adapted mapping is shared under CC BY-SA 4.0 and any further adaptation of it must carry the same licence. MCP and IETF RFC references are summarised in original wording. Check the current OWASP lists and specifications before use; example values are illustrative. Template licence: MIT.