This record as markdown: /tools/io-fusionauth-mcp-api/updatelambdawithid.md
What updateLambdaWithId does on Fusionauth
AI agents use updateLambdaWithId to create or update resources in Fusionauth, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Fusionauth environment.
Why updateLambdaWithId is rated Medium
This is a Write operation because it modifies existing lambda resources reversibly. However, it carries high severity because lambdas in FusionAuth control core authentication and authorization logic—misconfigured or malicious lambdas could compromise security across the system, even though the action itself is theoretically reversible.
From the tool's definition Tool name 'updateLambdaWithId' and description 'Updates the lambda with the given Id' indicate modification of existing data (lambda configuration/code).
Attacks that exploit this kind of access
The rule that runs updateLambdaWithId safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Fusionauth, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For updateLambdaWithId, this is the rule to start with:
updateLambdaWithId 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.
The button opens the PolicyLayer dashboard: create your workspace, connect Fusionauth, apply this rule, and every updateLambdaWithId call is checked against it from then on.
Questions about updateLambdaWithId
Updates the lambda with the given Id. It is categorised as a Write tool in the Fusionauth MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Fusionauth MCP server in PolicyLayer and add a rule for updateLambdaWithId: 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 Fusionauth. Nothing to install.
updateLambdaWithId 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 updateLambdaWithId 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 updateLambdaWithId. 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.
updateLambdaWithId is provided by the Fusionauth MCP server (@fusionauth/mcp-api). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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