AI agents call get_user_by_username to retrieve information from X(Twitter) V2 MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves user profile information by username from Twitter/X API v2. It performs a query operation with no data modification, deletion, or external execution. The blast radius is minimal - at worst, an AI agent could retrieve information about any public Twitter user, which is already publicly available. No authentication bypass or private data exposure is implied.
From the tool's definition Tool name 'get_user_by_username' indicates data retrieval. Server description states the MCP server enables 'retrieve tweets, post content, reply, quote, and more' - retrieval is listed as a core read function.
Documented attack patterns abuse exactly the kind of access get_user_by_username gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and X(Twitter) V2 MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for get_user_by_username:
{
"version": "1",
"default": "deny",
"tools": {
"get_user_by_username": {}
}
}get_user_by_username is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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get_user_by_username. It is categorised as a Read tool in the X(Twitter) V2 MCP Server MCP Server, which means it retrieves data without modifying state.
Register the X(Twitter) V2 MCP Server MCP server in PolicyLayer and add a rule for get_user_by_username: 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 X(Twitter) V2 MCP Server. Nothing to install.
get_user_by_username 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 get_user_by_username 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 get_user_by_username. 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.
get_user_by_username is provided by the X(Twitter) V2 MCP Server MCP server (nexusx-mcp/x-v2-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from X(Twitter) V2 MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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16 X(Twitter) V2 MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.