Replace the binary for an existing image in-place.
AI agents use update_image to create or update resources in Docx — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Docx environment.
The tool modifies existing image content within a Word document by replacing its binary data. This is a reversible write operation (the original image can theoretically be restored from backups or undo history), distinguishing it from destructive deletion. The scope is limited to image replacement within documents managed by the server, giving it medium severity rather than high.
From the tool's definition Tool description: 'Replace the binary for an existing image in-place.' The verb 'replace' indicates modification of existing data (the image binary), which is a write operation. The Word document structure is altered but not deleted or destroyed.
Documented attack patterns abuse exactly the kind of access update_image gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Docx, and nothing reaches the server without passing your rules. This is the rule we recommend for update_image:
{
"version": "1",
"default": "deny",
"tools": {
"update_image": {
"limits": [
{
"counter": "update_image_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}update_image 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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Replace the binary for an existing image in-place. It is categorised as a Write tool in the Docx MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Docx MCP server in PolicyLayer and add a rule for update_image: 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 Docx. Nothing to install.
update_image 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 update_image 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 update_image. 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.
update_image is provided by the Docx MCP server (securityronin/docx-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Docx, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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219 Docx tools catalogued and risk-classified — across an index of 43,000+ MCP servers.