You can change the password for a user account with the Api.ChangePassword method. Recommendation: Before changing a password, read the password policy from the CPU using the Api.GetPasswordPolicy API method. If the new password does not conform to the password policy of the CPU, a corresponding ...
AI agents use Api-ChangePassword to create or update resources in ThinkPLC-MCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your ThinkPLC-MCP environment.
This tool creates or modifies data (user account password) reversibly. While password changes are critical security operations, they are not destructive (the old password still exists in logs/backups), not financial, and not code execution.
From the tool's definition The tool description explicitly states 'You can change the password for a user account with the Api.ChangePassword method' and requires 'you must enter the current password for this call.' This modifies user account credentials, which is a reversible but…
Documented attack patterns abuse exactly the kind of access Api-ChangePassword gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and ThinkPLC-MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for Api-ChangePassword:
{
"version": "1",
"default": "deny",
"tools": {
"Api-ChangePassword": {
"limits": [
{
"counter": "api-changepassword_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}Api-ChangePassword 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.
Free to start. No card required.
You can change the password for a user account with the Api.ChangePassword method. Recommendation: Before changing a password, read the password policy from the CPU using the Api.GetPasswordPolicy API method. If the new password does not conform to the password policy of the CPU, a corresponding error message is returned. No prior authorizations are required to call the Api.ChangePassword method, but you must enter the current password for this call. Possible error messages: 5 System is read-only || The memory card is write-protected. Therefore, the password cannot be changed. 6 Not accepted || The password change is not performed because a CPU was configured with firmware version < V3.1. The method can only be used with CPUs as of firmware version V3.1. 100 Login failed || The user name and password combination is invalid. Assign a permissible user name and a permissible password. Another reason why the login failed may be an active brute force attack. 103 New password does not follow password policy || The provided new password does not match with the required password policy. Assign a password conforming to the password policy. The Api.GetPasswordPolicy method provides you with the password policy of the CPU, if the CPU is in. It is categorised as a Write tool in the ThinkPLC-MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the ThinkPLC- MCP server in PolicyLayer and add a rule for Api-ChangePassword: 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 ThinkPLC-MCP. Nothing to install.
Api-ChangePassword 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 Api-ChangePassword 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 Api-ChangePassword. 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.
Api-ChangePassword is provided by the ThinkPLC- MCP server (mrwan84/thinkplc-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from ThinkPLC-MCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
23 ThinkPLC-MCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.