Env var prefix risk

What mcp-scan saw

With requiredEnvVarPrefix set in .mcp-scan.json, the scan loop tested every key in the server's env block with startsWith against that prefix and reported each one that does not match. The comparison is case-sensitive and produces one finding per non-matching key.

Why it fires

A prefix convention is what makes it possible to tell at a glance which variables an MCP server is allowed to read, which matters because env is inherited and a server can read far more than its own block. This is a policy rule, so it only exists once your team turns it on.

When this is a false positive

• Third-party servers hardcode their variable names. GITHUB_TOKEN, ANTHROPIC_API_KEY, and DATABASE_URL are read by name inside the package and cannot be renamed to fit your prefix.
• The check is case-sensitive, so a prefix of MYCO_ does not match myco_ and reports keys that follow the convention in spirit.
• It fires once per key, so a server with six standard variables produces six findings for one policy decision.
• The prefix in .mcp-scan.json may have been inherited from another repo. An empty string matches everything, so the rule is off by default.

How to fix it

1. Open .mcp-scan.json and read requiredEnvVarPrefix. That value is the whole rule.
2. For variables you control, rename them to carry the prefix and update the server that reads them.
3. For third-party variables with fixed names, you cannot rename them. Decide whether the convention is worth the noise it produces on every such server.
4. If the convention only applies to your own servers, set requiredEnvVarPrefix to an empty string and enforce it in code review instead.
5. To suppress, add 'env-var-prefix-risk' to suppressRules in .mcp-scan.json.