AI agents use a2a_broadcast to create or update resources in Wmux — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Wmux environment.
This tool writes data (messages) to multiple workspaces, making it a Write operation. It is not Read (retrieves nothing), Execute (no code/command execution), Destructive (messages can be deleted/cleared), or Financial. Severity is medium because broadcasting to all workspaces could cause widespread disruption or confusion if misused by an agent, but messages are not permanent and reversible.
From the tool's definition Tool description states 'Send a message to ALL other workspaces at once', indicating it creates/writes messages to multiple recipients with reversible effect.
Attacks that exploit this kind of access
Send a message to ALL other workspaces at once (e.g. announcements, greetings). For targeted messages, use a2a_task_send instead. It is categorised as a Write tool in the Wmux MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Wmux MCP server in PolicyLayer and add a rule for a2a_broadcast: 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 Wmux. Nothing to install.
a2a_broadcast 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 a2a_broadcast 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 a2a_broadcast. 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.
a2a_broadcast is provided by the Wmux MCP server (openwong2kim/wmux). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
a2a_broadcast is one line of Wmux's registry record.
The record carries the whole server: verified identity, auth posture, risk grade, every tool classified, recommended policy — re-checked continuously.
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