get_free_busy
AI agents call get_free_busy to retrieve information from Zimbra MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
get_free_busy retrieves calendar availability data without creating, modifying, or deleting any information. It is a read-only query operation typical of calendar systems. No side effects or data mutations occur. Severity is low because the blast radius of misuse is limited to information disclosure of calendar availability, which is relatively benign compared to other operations on this server.
From the tool's definition Tool name 'get_free_busy' indicates querying calendar availability status. The Zimbra server description states it 'supports searching' and 'managing calendar events,' and this tool retrieves free/busy information without modifying data.
Attacks that exploit this kind of access
get_free_busy. It is categorised as a Read tool in the Zimbra MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Zimbra MCP Server MCP server in PolicyLayer and add a rule for get_free_busy: 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 Zimbra MCP Server. Nothing to install.
get_free_busy 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 get_free_busy 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 get_free_busy. 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.
get_free_busy is provided by the Zimbra MCP Server MCP server (jeremie-lesage/zimbra-mcp). 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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