AI agents call list_customers to retrieve information from Fortnox without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves and queries customer data without creating, modifying, deleting, or executing operations. It has no side effects on the accounting system beyond fetching information. The low severity reflects minimal blast radius—an AI agent listing customers poses no risk of data loss, financial harm, or unwanted modifications.
From the tool's definition Tool description states 'Search and filter the customer database' with no mention of modification, deletion, or side effects. The verb 'list' and action words 'search and filter' are consistent with read-only data retrieval operations.
Attacks that exploit this kind of access
Search and filter the customer database. It is categorised as a Read tool in the Fortnox MCP Server, which means it retrieves data without modifying state.
Register the Fortnox MCP server in PolicyLayer and add a rule for list_customers: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Fortnox. Nothing to install.
list_customers is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the list_customers rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for list_customers. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
list_customers is provided by the Fortnox MCP server (proviscale/fortnox-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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