AI agents use cache_prepend to create or update resources in Awslabs Amazon Sns Sqs — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Awslabs Amazon Sns Sqs environment.
The tool modifies existing data by prepending a string, which is a reversible write operation. However, the description is minimal and the tool name 'cache_prepend' suggests it operates on a cache value. The context (SNS/SQS server) is somewhat inconsistent with a cache operation, lowering confidence. Assuming it modifies cache entries, it falls under Write as data is altered but not destroyed.
From the tool's definition 'Prepend a string to an existing value' — modifies existing data by prepending content
Documented attack patterns abuse exactly the kind of access cache_prepend gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Awslabs Amazon Sns Sqs, and nothing reaches the server without passing your rules. This is the rule we recommend for cache_prepend:
{
"version": "1",
"default": "deny",
"tools": {
"cache_prepend": {
"limits": [
{
"counter": "cache_prepend_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}cache_prepend 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.
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Prepend a string to an existing value. It is categorised as a Write tool in the Awslabs Amazon Sns Sqs MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Awslabs Amazon Sns Sqs MCP server in PolicyLayer and add a rule for cache_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 Awslabs Amazon Sns Sqs. Nothing to install.
cache_prepend 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 cache_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.
Set action: deny in the PolicyLayer policy for cache_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.
cache_prepend is provided by the Awslabs Amazon Sns Sqs MCP server (awslabs.amazon-sns-sqs-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Awslabs Amazon Sns Sqs, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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