AI agents call cal_list_calendars to retrieve information from M365 without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool queries and returns calendar data without modifying, executing, or deleting anything. It is a straightforward read operation that retrieves metadata about the user's calendars. The blast radius of misuse is low—an attacker gains visibility into calendar structure but cannot modify events, delete calendars, or trigger external actions.
From the tool's definition Tool name 'cal_list_calendars' and description 'List all calendars in the user' indicate a retrieval operation with no side effects.
Attacks that exploit this kind of access
List all calendars in the user\. It is categorised as a Read tool in the M365 MCP Server, which means it retrieves data without modifying state.
Register the M365 MCP server in PolicyLayer and add a rule for cal_list_calendars: 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 M365. Nothing to install.
cal_list_calendars 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 cal_list_calendars 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 cal_list_calendars. 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.
cal_list_calendars is provided by the M365 MCP server (swamirama/m365-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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