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proton-mail-bridge-client MCP Server Security Report

googlarz/proton-mail-bridge-client

Local-first Proton Mail MCP server and CLI via Proton Bridge. Search, draft, send and organize mail from Claude Desktop, Claude Code or any MCP client. 96 tools, read-only and send-to-self modes.

Security Trust Score
Grade F · Serious issues
Tier 1 · Public sourceHigh confidence · 98%latest vmain@643676d Repository
Declared MCP capabilities
ResourcesPrompts

Run it securely

This server scored F. Run it behind runtime policy enforcement so one bad tool call can't become an incident.

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2 issues capping this score
  • criticalNo command-injection sinks — 2 occurrences
  • mediumNo over-broad / destructive tools — 1 over-broad tool(s)

The short answer

Is proton-mail-bridge-client safe to use?
proton-mail-bridge-client scores 15/100 (grade F) on the Canopii Trust Index, and carries 2 confirmed security failures that cap its score: No command-injection sinks and No over-broad / destructive tools. It passes 14 of the 21 controls that apply to it.
What security issues does proton-mail-bridge-client have?
proton-mail-bridge-client fails 2 controls: No command-injection sinks and No over-broad / destructive tools. Each failure on this page carries the evidence behind it — the file and line, dependency, or CVE that decided it.
How reliable is the security score for proton-mail-bridge-client?
We could evaluate 98% of the controls that apply to proton-mail-bridge-client. Scores are deterministic — the same source always produces the same score — and a partially-scannable server cannot present a high one, because confidence caps the result. The scanner is open source, so this score can be reproduced independently.
How was proton-mail-bridge-client scored?
Its published source was scanned against a fixed catalog of weighted security controls covering code safety, committed secrets, dependency vulnerabilities, tool-description integrity, authentication and transport, and maintenance. A confirmed flaw caps the score outright regardless of what else passes. The full rubric is published.
Reputation85stars19forks1open issues2d agolast commit<1yage

Security controlslatest scored version vmain@643676d

Each control is evaluated deterministically with evidence. The score is earned from passing controls; a failed guard caps it.

Model–MCP Runtime Guardrails

  • Fail
    User-in-the-Loop / Approval Scopeguard1 over-broad tool(s)

    No over-broad or destructive tools (arbitrary shell, bulk-delete) that warrant human approval. How many servers fail this?

    delete_email

    Fix: Scope tools narrowly; avoid arbitrary command execution and destructive defaults.

  • Warn
    Strict JSON Schema Enforcementschemas not strict

    Tool inputs are constrained (additionalProperties:false), so unexpected arguments can't be smuggled in.

    Fix: Set additionalProperties:false and require explicit parameters on every tool.

  • Pass
    Indirect Prompt Injection (IPI) Defensesguardno injection markers

    Tool/prompt/resource text is free of hidden instructions that could hijack the agent.

  • Pass
    Tool Definition Integrityguardtool definitions stable; no risky changes in version history

    Every consecutive version pair is diffed for new injection markers or destructive scope — a risky diff anywhere in history is a rug-pull (fail, durable); benign description drift warns.

Application Security Checks

  • Fail
    No command-injection sinksguard2 occurrences

    Untrusted tool input reaching a shell yields remote code execution. How many servers fail this?

    src/config-env.ts:37src/config-env.ts:250

    Fix: Never pass tool arguments to a shell; use argv arrays with shell disabled.

  • Warn
    No path traversalguard77 occurrences

    Naive path checks let tools read/write outside intended directories (EscapeRoute-class).

    scripts/homebrew-formula.mjs:73src/cli.ts:87src/cli.ts:99src/cli.ts:990

    Fix: Resolve to a canonical path and verify containment; reject ../ and symlinks.

  • Warn
    No SSRF sinksguard1 occurrence

    Fetching tool-supplied URLs can pivot into internal networks and metadata services.

    src/services/embedding-service.ts:235

    Fix: Allow-list destinations; reject arbitrary/loopback/link-local URLs.

  • Pass
    No dynamic code executionguardno sinks found

    eval()/exec()/Function() on tool-derived strings allows arbitrary code execution.

  • Pass
    No unsafe deserializationguardno sinks found

    pickle/yaml.load/etc. on untrusted data can execute code.

  • Pass
    No committed secretsguardno secrets found

    Hardcoded keys/tokens in published source are live credentials an attacker can use.

  • Pass
    Credentials sourced from environmentreads credentials from environment

    Reading secrets from env/secret stores avoids hardcoding them.

  • Pass
    No known-vulnerable dependencies151 runtime deps, no known CVEs

    Runtime dependencies (parsed from the lockfile) are scanned against OSV.dev for published CVEs. Advisory: flagged dependencies lower the score but don't hard-cap it, since transitive reachability is unproven.

  • Pass
    Dependencies pinned (lockfile)lockfile present

    A lockfile makes installs reproducible and resistant to silent dependency swaps.

  • Pass
    Actively maintainedrecent commits

    Unmaintained servers don't receive security fixes.

  • Pass
    Repository not archivedguardactive

    Archived repositories will never be patched.

  • Pass
    Declares a licenseMIT

    A clear license is required for legal enterprise use.

  • Pass
    Has a security policySECURITY.md present

    A SECURITY.md gives a private path to report vulnerabilities.

  • Pass
    Adoption & popularityestablished adoption

    A small, capped nudge from stars/downloads — widely-used servers get more eyes on bugs. It can never offset a real security failure.

  • Not checked
    Signed releasesnot evaluated

    Signed releases let consumers verify artifacts weren't tampered with.

  • N/A
    No install/post-install scriptsguardno published package

    install hooks run arbitrary code on every consumer at install time.

  • N/A
    Package name not typosquattingguardno published package

    Names mimicking popular packages are a common malware delivery vector.

  • N/A
    Published with provenanceno published package

    Build provenance attests the artifact was built from the claimed source by CI.

  • N/A
    Established maintainerno published package

    Brand-new / single anonymous maintainers raise takeover and malware risk.

Transport & Trust Model

  • Warn
    Network Exposurebinds 0.0.0.0

    Binding 0.0.0.0 or exposing debug inspectors widens the attack surface.

    Fix: Bind to 127.0.0.1 by default; never ship open debug endpoints.

  • Pass
    Execution Sandboxingcontainerized

    A container/sandbox image limits blast radius; a server that runs natively has full host access.

  • N/A
    Transport Encryption (TLS)guardno remote endpoints

    Plaintext HTTP exposes traffic and bearer tokens to interception.

  • N/A
    IAM / Authentication Scopingno remote endpoints

    OAuth 2.1 / Protected Resource Metadata gates who can invoke tools.

  • N/A
    Live Endpoint Reachablenot dynamically scanned

    A dynamic scan connected to the declared remote endpoint and it responded — verified live, not a dead URL.

  • N/A
    Authentication Enforced (live)not dynamically scanned

    If the server declares auth is required, it must actually reject anonymous clients. Serving tools to unauthenticated callers is a real exposure.

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Versions

VersionScoreStatus
vmain@643676dlatest15Fscored
vmain@db6939c15Fscored
vmain@4ba9e4b15Fscored
vmain@04365a015Fscored
vmain@3d5fc8f16Fscored
vmain@6c805fa15Fscored
vmain@51842cb15Fscored
vmain@738819816Fscored
vmain@4f48c2b89Bscored
vmain@4cdfc3693Ascored
vmain@ebcc64593Ascored
vmain@9c0db4393Ascored
vmain@e6f86ae93Ascored
vmain@7c7002e92Ascored
vmain@0e4e0ad92Ascored
vmain@a32ff5093Ascored
vmain@7ed56cc93Ascored
vmain@b90aa6c93Ascored
vmain@0728f7f93Ascored
vmain@815a05689Bscored
vmain@d58166289Bscored
vmain@e91bbe889Bscored
vmain@47fc10089Bscored
vmain@477199189Bscored
vmain@e5ac19989Bscored
vmain@811be5d89Bscored
vmain@741427a89Bscored
vmain@8d5666289Bscored
vmain@c60941a88Bscored

Wondering how this compares? The MCP Security Index tracks grade distribution, committed secrets, and missing authentication across the whole ecosystem, refreshed monthly.