AI agents call browser_cookies to retrieve information from Wmux without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool spans Read and Write (get vs set/clear), so by severity rules the most impactful operation applies. Setting or clearing cookies can modify authentication state and session data — a Write-level action. However, the most dangerous misuse is reading authentication/session cookies (even with the sensitive-domain guard), which could expose credentials.
From the tool's definition Manage browser cookies: get, set, or clear. Reads from sensitive domains (email, banking, auth) are blocked and values from such domains are redacted unless allowSensitiveDomains:true is set.
Attacks that exploit this kind of access
Manage browser cookies: get, set, or clear. Reads from sensitive domains (email, banking, auth) are blocked and values from such domains are redacted unless allowSensitiveDomains:true is set. It is categorised as a Read tool in the Wmux MCP Server, which means it retrieves data without modifying state.
Register the Wmux MCP server in PolicyLayer and add a rule for browser_cookies: 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.
browser_cookies 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 browser_cookies 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 browser_cookies. 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.
browser_cookies 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.
browser_cookies 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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