Write data to a file. If it exists, create a numbered backup (e.g., file.1.csv).
AI agents use write_file_backup to create or update resources in File Writer — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your File Writer environment.
This tool creates or modifies data reversibly. It writes to files but preserves prior versions through automatic backups, so data loss is not irreversible. The blast radius is medium: uncontrolled file writes could corrupt critical documents, fill disk space, or overwrite important configurations within the restricted root directory, but the backup mechanism mitigates some risk.
From the tool's definition Tool name is 'write_file_backup' and description states 'Write data to a file'. The backup mechanism (creating numbered backups of existing files) demonstrates reversibility—the original data is preserved, not deleted.
Attacks that exploit this kind of access
Write data to a file. If it exists, create a numbered backup (e.g., file.1.csv). It is categorised as a Write tool in the File Writer MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the File Writer MCP server in PolicyLayer and add a rule for write_file_backup: 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 File Writer. Nothing to install.
write_file_backup 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 write_file_backup 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 write_file_backup. 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.
write_file_backup is provided by the File Writer MCP server (thekogit/file_writer_mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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