AI agents use upload_attachment to create or update resources in Basecamp MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Basecamp MCP Server environment.
This tool creates new data (file attachments) in a reversible manner—uploads can be deleted or replaced. It is not destructive (no irreversible deletion), not financial, and not execute-class (no arbitrary code/command execution). The severity is medium because bulk uploads or attachment spam could consume storage or create data clutter, but the blast radius is limited to attachment objects within Basecamp projects.
From the tool's definition Tool name 'upload_attachment' and description 'Upload a file attachment' indicate file creation/storage. Basecamp API context confirms this creates new data objects (attachments) in the project management system.
Documented attack patterns abuse exactly the kind of access upload_attachment gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Basecamp MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for upload_attachment:
{
"version": "1",
"default": "deny",
"tools": {
"upload_attachment": {
"limits": [
{
"counter": "upload_attachment_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}upload_attachment 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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Upload a file attachment. It is categorised as a Write tool in the Basecamp MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Basecamp MCP Server MCP server in PolicyLayer and add a rule for upload_attachment: 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 Basecamp MCP Server. Nothing to install.
upload_attachment 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 upload_attachment 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 upload_attachment. 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.
upload_attachment is provided by the Basecamp MCP Server MCP server (qusaiisaleem/basecamp-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Basecamp 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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56 Basecamp MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.