AI agents use cancel_auto_merge to create or update resources in Gitlab — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Gitlab environment.
Cancelling auto-merge modifies the state of a merge request by removing its scheduled auto-merge configuration. This is a reversible write operation (auto-merge can be re-enabled), not a destructive action since no data is deleted. The blast radius is medium as it affects the CI/CD workflow but doesn't delete code or pipelines.
From the tool's definition Cancel auto-merge for a merge request
Documented attack patterns abuse exactly the kind of access cancel_auto_merge gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Gitlab, and nothing reaches the server without passing your rules. This is the rule we recommend for cancel_auto_merge:
{
"version": "1",
"default": "deny",
"tools": {
"cancel_auto_merge": {
"limits": [
{
"counter": "cancel_auto_merge_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}cancel_auto_merge 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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Cancel auto-merge for a merge request. It is categorised as a Write tool in the Gitlab MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Gitlab MCP server in PolicyLayer and add a rule for cancel_auto_merge: 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 Gitlab. Nothing to install.
cancel_auto_merge 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 cancel_auto_merge 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 cancel_auto_merge. 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.
cancel_auto_merge is provided by the Gitlab MCP server (yoda-digital/mcp-gitlab-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 88 Gitlab tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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88 Gitlab tools catalogued and risk-classified — across an index of 42,500+ MCP servers.