cms_upload_asset_from_base64
Upload a small asset inline as base64 (≤100 KB decoded). The right choice when you have generated the asset in this conversation (image-gen output, screenshot, plot) and need it in the CMS without leaving the chat: compress to WebP or JPEG well under 100 KB first, then pass the bytes here. SVG is...
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What cms_upload_asset_from_base64 does on Munin
AI agents use cms_upload_asset_from_base64 to create or update resources in Munin, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Munin environment.
Why cms_upload_asset_from_base64 is rated Medium
The tool creates and stores new assets in the CMS system, making it a Write action. Severity is medium because: (1) it has built-in constraints (≤100 KB, no SVG) that limit damage scope, (2) uploads are generally reversible (assets can be deleted), and (3) the impact is localized to media storage rather than core data or user accounts.
From the tool's definition Tool description states "Upload a small asset inline as base64", which is a create/write operation that adds new data to the CMS. The description explicitly frames this as uploading/storing content.
Attacks that exploit this kind of access
The rule that runs cms_upload_asset_from_base64 safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Munin, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For cms_upload_asset_from_base64, this is the rule to start with:
cms_upload_asset_from_base64 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.
The button opens the PolicyLayer dashboard: create your workspace, connect Munin, apply this rule, and every cms_upload_asset_from_base64 call is checked against it from then on.
Questions about cms_upload_asset_from_base64
Upload a small asset inline as base64 (≤100 KB decoded). The right choice when you have generated the asset in this conversation (image-gen output, screenshot, plot) and need it in the CMS without leaving the chat: compress to WebP or JPEG well under 100 KB first, then pass the bytes here. SVG is rejected. For larger assets reachable over HTTPS use. It is categorised as a Write tool in the Munin MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Munin MCP server in PolicyLayer and add a rule for cms_upload_asset_from_base64: 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 Munin. Nothing to install.
cms_upload_asset_from_base64 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 cms_upload_asset_from_base64 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 cms_upload_asset_from_base64. 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.
cms_upload_asset_from_base64 is provided by the Munin MCP server (https://mcp.getmunin.com/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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