Set UNIX permissions on a file or directory. Can optionally apply recursively and strip existing ACLs.
AI agents use filesystem_set_permissions to create or update resources in Truenas — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Truenas environment.
This tool modifies file and directory permissions, which are write operations that change system state. While permission changes are technically reversible (can be undone by resetting to previous values), the impact is significant—incorrect permission assignments could lock out legitimate users or expose sensitive data.
From the tool's definition Tool description states it 'Set[s] UNIX permissions on a file or directory' and can 'apply recursively and strip existing ACLs'. This modifies filesystem metadata and access control configurations, which are reversible but impactful changes.
Documented attack patterns abuse exactly the kind of access filesystem_set_permissions gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Truenas, and nothing reaches the server without passing your rules. This is the rule we recommend for filesystem_set_permissions:
{
"version": "1",
"default": "deny",
"tools": {
"filesystem_set_permissions": {
"limits": [
{
"counter": "filesystem_set_permissions_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}filesystem_set_permissions stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
Free to start. No card required.
Set UNIX permissions on a file or directory. Can optionally apply recursively and strip existing ACLs. It is categorised as a Write tool in the Truenas MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Truenas MCP server in PolicyLayer and add a rule for filesystem_set_permissions: 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 Truenas. Nothing to install.
filesystem_set_permissions is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the filesystem_set_permissions 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 filesystem_set_permissions. 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.
filesystem_set_permissions is provided by the Truenas MCP server (spranab/truenas-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Truenas, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
279 Truenas tools catalogued and risk-classified — across an index of 43,000+ MCP servers.