Please report security vulnerabilities through GitHub's private vulnerability reporting, not a public issue:
Report a vulnerability (Security tab → "Report a vulnerability")
This opens a private advisory visible only to you and the maintainer, so the issue isn't publicly disclosed before a fix ships. Please include enough detail to reproduce it (steps, affected version/commit, expected vs. actual behavior).
Mill is a desktop app that executes guardrailed local commands and integrations on the user's behalf. Things that are in scope for a security report:
- A workflow, trigger, or MCP tool call bypassing the guardrail preview/ approval step and taking an action without the user seeing it first.
- Secrets (connector credentials, API keys) stored anywhere other than the OS keychain, or leaking into logs, exported workflows, or the frontend.
- The MCP listener: Mill exposes a local, unauthenticated MCP server bound
to
127.0.0.1(loopback-only, by design — it never binds a non-loopback interface and is not reachable off the local machine). A report that it is reachable off-machine, or that a loopback process without the user's intent can drive it, is in scope. A report that "it has no auth" on its own is expected/by-design for a loopback listener and not itself a vulnerability, unless it demonstrates cross-boundary reachability. - Arbitrary command/code execution reachable without going through the guardrail (i.e. a path that runs something the user never previewed or approved).
Out of scope: vulnerabilities requiring an already-compromised machine, social engineering, or issues in third-party dependencies without a demonstrated Mill-specific exploit path (report those upstream; Mill still wants to know if it makes a dependency's issue reachable in a novel way).
Mill is pre-1.0. There are no released version branches yet — the only
supported line is the latest commit on main. Fixes land there; there is
no backport policy until a 1.0 release establishes one.