AI agents call compare_files to retrieve information from MCP Filesystem Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
The compare_files tool performs a non-destructive comparison operation. It retrieves content from two files and displays their differences, which is a pure read operation with no capability to modify, delete, or execute code. The low severity reflects minimal risk even if misused by an AI agent, as the worst outcome would be information disclosure of already-accessible files.
From the tool's definition Tool description states 'Compare two text files and show differences' - a read-only operation that retrieves and displays file content without modification or side effects.
Documented attack patterns abuse exactly the kind of access compare_files gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and MCP Filesystem Server, and nothing reaches the server without passing your rules. This is the rule we recommend for compare_files:
{
"version": "1",
"default": "deny",
"tools": {
"compare_files": {}
}
}compare_files is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Compare two text files and show differences. It is categorised as a Read tool in the MCP Filesystem Server MCP Server, which means it retrieves data without modifying state.
Register the MCP Filesystem Server MCP server in PolicyLayer and add a rule for compare_files: 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 MCP Filesystem Server. Nothing to install.
compare_files 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 compare_files 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 compare_files. 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.
compare_files is provided by the MCP Filesystem Server MCP server (safurrier/mcp-filesystem). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 21 MCP Filesystem Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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21 MCP Filesystem Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.