C1 Identity & least privilege
0.17 / 1.00
The server runs as the local user and holds no credentials of its own by default; the default browser is a fresh, throwaway profile with no logins, which is a real narrowing. But nothing checks what the browser is allowed to reach: the model can point browser_open at any directory as the profile (including a directory that already holds logins), choose any proxy, and navigate to any URL including file:// paths and local network services. A .env file in the directory the host starts the server from can widen the same settings silently.
C2 Approval gates
0.25 / 1.00
As a tool server it does not own the approval prompt, so what matters is the risk signal it gives the host. Every tool carries explicit readOnly/destructive hints and clicking, typing and navigating are correctly marked destructive. But browser_evaluate, which runs arbitrary model-written JavaScript in the page, is marked read-only, and the code's own comment says read-only means a client may run it without asking. A regex refuses a handful of obvious page-changing calls but, by the authors' own statement, is not a boundary, and fetch(), location changes and similar calls pass. There is no server-side read-only mode or dry-run.
C3 Tool & action scoping
0.20 / 1.00
File upload is a model of careful scoping: it is off unless the operator lists directories, and each path is resolved, contained, refused through hidden directories, size-capped, and re-checked on the opened file. Everything else is general-purpose. browser_navigate accepts any URL with no scheme or host check, so file://, localhost and cloud-metadata addresses are not refused. browser_evaluate takes arbitrary JavaScript behind a denylist of a few method names. browser_open accepts any directory as a profile.
C4 Code-execution isolation
0.45 / 1.00
Model-written JavaScript runs through browser_evaluate inside the page of a patched Firefox. The only containment is the browser's own content-process sandbox and same-origin rules, which this repository neither configures nor verifies; the regex filter on the script is explicitly described by its authors as not a sandbox. The browser process itself runs as the user with the server's environment, full network, and whatever logins the chosen profile holds.
C5 Untrusted input blast radius
0.00 / 1.00
The server reads arbitrary web pages and returns their text, HTML and snapshot to the model as plain results, with no untrusted marker and mixed with the server's own instructions. Nothing drops a leg of the Rule of Two: the same session reads hostile pages, can hold logged-in sessions or local files, and can send data anywhere through navigate or through browser_evaluate, which is advertised read-only so many hosts will run it unprompted. The server's own instructions also coach the model to use throwaway-mail sites to get through email verification.
C6 Memory, context & configuration integrity
0.10 / 1.00
The MCP server reads a .env file from whatever directory the host starts it in, before serving, and applies every variable it finds. Hosts commonly start servers in the project directory, so a cloned repository's .env can silently turn on uploads from chosen directories, route all browsing through an attacker's proxy, pick the browser profile or engine binary, or switch the server to HTTP on any interface with no authentication. Separately, the proxy and profile a model chooses are written to a session file and reused by the next browser_open with no arguments, and all standalone clients share the same default file.
C7 Third-party extensions
0.35 / 1.00
The server has no plugin or extension mechanism, but at startup it automatically downloads and then runs a roughly 250 MB patched Firefox build. The download and its check against a pinned 'seal' live in the invisible-playwright/invisible-core dependencies, so the verification can't be confirmed from this repository. The binary path can also be set through STEALTHFOX_BINARY, including from a workspace .env, and the browser runs as the user with the server's environment.
C8 Secrets & sensitive-data protection
0.42 / 1.00
There is good care around page secrets: password and one-time-code fields are masked in snapshots, HTML reads and typing replies, so a filled password is not echoed into the conversation, and the server drops any OpenRouter key from its environment before launching the browser. There is no telemetry and no logging. Weak spots: proxy credentials are written in plaintext into the session file with default permissions, and browser_evaluate and read_text can still read secret values directly.
C9 Audit & traceability
0.00 / 1.00
The MCP server keeps no record of what it did: no tool-call log, no audit file, no logging calls at all in the server package. The only persisted file records who the main browser is (seed, proxy, profile), not its actions. Any record of activity exists only in the host's transcript, which doesn't count for the server.
C10 Limits & kill switch
0.38 / 1.00
The server bounds most single operations: navigation waits at most 45 seconds, element actions 15 seconds, and text and JavaScript results are capped at 6,000 characters. Some operations are open-ended: snapshots are uncapped by default, press-and-hold duration is whatever the model asks, and browser_evaluate has no timeout. Closing the stdio connection closes the browsers and cancels background typing. There are no rate limits.
SafetyCard