Attach a file to a task. Provide the absolute file path and the MCP server reads it directly from disk.
AI agents use blob_attach to create or update resources in Flux MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Flux MCP Server environment.
This operation modifies task state by attaching a file, which is a reversible write operation (the attachment can be removed). It does not execute arbitrary code, delete data irreversibly, or move money.
From the tool's definition Tool description states 'Attach a file to a task', which creates or modifies task data by adding a file attachment. The tool reads from disk and binds that content to a task entity.
Documented attack patterns abuse exactly the kind of access blob_attach gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Flux MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for blob_attach:
{
"version": "1",
"default": "deny",
"tools": {
"blob_attach": {
"limits": [
{
"counter": "blob_attach_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}blob_attach 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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Attach a file to a task. Provide the absolute file path and the MCP server reads it directly from disk. It is categorised as a Write tool in the Flux MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Flux MCP Server MCP server in PolicyLayer and add a rule for blob_attach: 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 Flux MCP Server. Nothing to install.
blob_attach 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 blob_attach 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 blob_attach. 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.
blob_attach is provided by the Flux MCP Server MCP server (sirsjg/flux). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 25 Flux MCP Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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25 Flux MCP Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.