AI agents use hash_set to create or update resources in MCP Server Redis — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your MCP Server Redis environment.
The tool sets (creates or modifies) multiple fields within a Redis hash. This is a Write operation because it modifies data reversibly without irreversibly deleting or executing arbitrary logic. Severity is medium because misuse could corrupt application state or overwrite important cached data, but the operation is reversible through subsequent hash_set or delete operations.
From the tool's definition Tool name 'hash_set' and description 'Set multiple hash fields' indicate creation or modification of hash data structure fields in Redis.
Documented attack patterns abuse exactly the kind of access hash_set gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and MCP Server Redis, and nothing reaches the server without passing your rules. This is the rule we recommend for hash_set:
{
"version": "1",
"default": "deny",
"tools": {
"hash_set": {
"limits": [
{
"counter": "hash_set_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}hash_set 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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Set multiple hash fields. It is categorised as a Write tool in the MCP Server Redis MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the MCP Server Redis MCP server in PolicyLayer and add a rule for hash_set: 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 MCP Server Redis. Nothing to install.
hash_set 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 hash_set 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 hash_set. 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.
hash_set is provided by the MCP Server Redis MCP server (prajwalnayak7/mcp-server-redis). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from MCP Server Redis, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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10 MCP Server Redis tools catalogued and risk-classified — across an index of 43,000+ MCP servers.