Overwrite part of string. Args: key: The name of the key offset: Position to start overwriting value: String to write Returns: Success message or error message
AI agents use string_set_range to create or update resources in AWS — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your AWS environment.
This tool writes or modifies data in a reversible manner. While 'overwrite' could seem destructive, it is modifying a string value rather than deleting the entire key or data structure. The operation is reversible through subsequent writes. However, without knowing the blast radius (whether this affects critical AWS configuration, secrets, or application data), severity is set to medium.
From the tool's definition Tool description states 'Overwrite part of string' with parameters for key, offset, and value. The operation modifies existing data (overwrite) but does not delete or irreversibly destroy it.
Documented attack patterns abuse exactly the kind of access string_set_range gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and AWS, and nothing reaches the server without passing your rules. This is the rule we recommend for string_set_range:
{
"version": "1",
"default": "deny",
"tools": {
"string_set_range": {
"limits": [
{
"counter": "string_set_range_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}string_set_range 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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Overwrite part of string. Args: key: The name of the key offset: Position to start overwriting value: String to write Returns: Success message or error message. It is categorised as a Write tool in the AWS MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the AWS MCP server in PolicyLayer and add a rule for string_set_range: 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 AWS. Nothing to install.
string_set_range 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 string_set_range 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 string_set_range. 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.
string_set_range is provided by the AWS MCP server (@awslabs/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from AWS, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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300 AWS tools catalogued and risk-classified — across an index of 43,000+ MCP servers.