list_prepend

THE RISK

High Risk

Why list_prepend needs a policy

The description is minimal and uninformative about what list is being modified or where it resides. 'Prepend value to list' suggests a write/modify operation on some data structure. Given the AWS Support MCP context and sibling tools, this likely modifies some internal list or data structure.

From the tool's definition Tool name: 'list_prepend', description: 'Prepend value to list.'

Documented attack patterns abuse exactly the kind of access list_prepend gives an agent:

POLICY

How to control list_prepend

PolicyLayer is an MCP gateway — it sits between your AI agents and AWS Support MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for list_prepend:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "list_prepend": {
      "limits": [
        {
          "counter": "list_prepend_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

list_prepend stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

Create a free account and register AWS Support MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

RATE-LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

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All 805 AWS Support MCP Server tools →

Execute tools on other servers

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Go deeper

Govern code and CI agents → Branch allowlists, approval on merges, and rate caps on the build and pipeline tools agents trigger.
High-risk tools in AWS Support MCP Server → Every high-risk tool this server exposes, in one view.
All high-risk MCP tools → Every high-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Agent sandbox → Bounding what an agent can execute and where the boundary should sit.
Least privilege for MCP → Granting agents the minimum tool surface the task needs.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →
PolicyLayer vs alternatives → How deterministic, per-call MCP policy compares with gateways, identity layers, and authorisation platforms.

FAQ

Questions about list_prepend

What does the list_prepend tool do? +

Prepend value to list. It is categorised as a Execute tool in the AWS Support MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on list_prepend? +

Register the AWS Support MCP Server MCP server in PolicyLayer and add a rule for list_prepend: 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 AWS Support MCP Server. Nothing to install.

What risk level is list_prepend? +

list_prepend is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit list_prepend? +

Yes. Add a rate_limit block to the list_prepend 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.

How do I block list_prepend completely? +

Set action: deny in the PolicyLayer policy for list_prepend. 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.

What MCP server provides list_prepend? +

list_prepend is provided by the AWS Support MCP Server MCP server (awslabs.aws-support-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every AWS Support MCP Server tool call.

Start from AWS Support MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →