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Darnit Security Guide

This document describes security considerations, best practices, and configuration options for using Darnit securely.

Table of Contents


Dynamic Module Loading Security

Darnit can import a Python attribute named in configuration as package.module:attribute: MCP tool handlers in [mcp.tools], handler references, and type = "python" adapters. Every such import goes through one function, darnit.core.handlers.resolve_module_path (framework-design.md 6.5).

Resolution Policy

  • The path must be a.b.c:attr, with every part a Python identifier. Relative paths, empty parts, and dotted attributes are refused.
  • The module's top-level package must be darnit, or the package of an implementation that discovery loaded from the darnit.implementations entry points (darnit_csl:register allows darnit_csl.*).
  • The allowed set is derived from installed entry point metadata. There is no list to extend: installing an implementation package allows its modules, and nothing else does.
  • The check runs before the import, so a refused module is never imported.

Failure Behavior

  • A refused path raises HandlerImportRefused (a ValueError) naming the path and the allowed packages, logged at WARNING.
  • At MCP server start, a tool whose handler is refused is not registered, and the server logs an ERROR naming the tool.

Security Implications

  • A configuration string cannot reach os, subprocess, or any other package that is not darnit or an installed implementation.
  • The policy is not a sandbox. Allowed packages are code the operator installed, and [mcp.tools] is read only from an installed framework TOML or an operator-supplied darnit serve <config.toml>, never from the audited repository.
  • To use your own adapter or tool module, ship it in a package registered under darnit.implementations.

GitHub Token Security

Darnit requires GitHub API access for many checks (branch protection, workflows, etc.).

Token Sources

Darnit obtains GitHub tokens in this order:

  1. GITHUB_TOKEN environment variable
  2. gh auth token (GitHub CLI authentication)

Required Permissions

For read-only auditing, your token needs:

Permission Scope Purpose
repo Read Access repository metadata, branch protection
read:org Read Check organization settings (if applicable)

For remediation (creating files, changing branch protection). darnit reads the current settings before any change, so a token that can write but not read protection settings changes nothing:

Permission Scope Purpose
repo Write Create/modify files, enable branch protection
workflow Write Modify GitHub Actions workflows

Best Practices

  1. Use fine-grained tokens with minimal permissions
  2. Never commit tokens to version control
  3. Rotate tokens regularly especially for CI/CD
  4. Use short-lived tokens in automated pipelines
  5. Audit token usage via GitHub's security log

CI/CD Configuration

# GitHub Actions example
jobs:
  audit:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      security-events: write
    steps:
      - uses: actions/checkout@v4
      - name: Run Darnit Audit
        env:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        run: |
          uv run python main.py audit_openssf_baseline

Custom Adapter Security

When creating custom adapters, follow these security guidelines.

Adapter Development Checklist

  • Validate all inputs from configuration and control definitions
  • Sanitize file paths to prevent path traversal attacks
  • Avoid shell injection when executing external commands
  • Handle secrets securely - never log credentials
  • Implement timeouts for external calls
  • Use least privilege - request only necessary permissions

Secure Command Execution

For command-based adapters, use safe execution patterns:

import subprocess
import shlex

class SecureCommandAdapter(CheckAdapter):
    def check(self, control_id, owner, repo, local_path, config):
        command = config.get("command", "")

        # NEVER do this - shell injection vulnerability
        # subprocess.run(f"tool {local_path}", shell=True)

        # DO this - use list arguments, no shell
        subprocess.run(
            ["tool", "--path", local_path],
            shell=False,
            timeout=300,
            capture_output=True,
        )

Input Validation

from pathlib import Path

def validate_path(path: str, allowed_base: str) -> Path:
    """Validate path is within allowed directory."""
    resolved = Path(path).resolve()
    allowed = Path(allowed_base).resolve()

    if not str(resolved).startswith(str(allowed)):
        raise ValueError(f"Path {path} is outside allowed directory")

    return resolved

Configuration Security

darnit separates two kinds of configuration:

  • Operator configuration is tool configuration owned by whoever runs darnit. It is the only place tool settings come from.
  • Project claims in .project/ are statements a repository makes about itself. They are reported, and they count only under the trust and evidence rules below.

Nothing in an audited repository can add to, override, or select operator configuration.

Operator Configuration

Operator configuration is a TOML file found the same way by every driver (CLI, MCP server, headless harness):

  1. --operator-config PATH given at launch (darnit audit, darnit run, darnit harness, darnit serve, darnit config show).
  2. Otherwise the per-user location: $XDG_CONFIG_HOME/darnit/config.toml when XDG_CONFIG_HOME is set and absolute, else ~/.config/darnit/config.toml (Linux and macOS), or %APPDATA%\darnit\config.toml (Windows).
  3. Otherwise built-in defaults.

It holds allowed plugins and trusted publishers, MCP servers, per-control pass overrides and custom controls, storage backends, LLM settings, trusted repositories, CI trust rules, policy defaults, and the remediation policy for platform changes (Remediation Safety):

schema_version = 1

[plugins]
allowed = ["openssf-baseline"]
trusted_publishers = ["https://github.com/darnitdevorg"]
allow_unsigned = false

[mcp_servers.scanner]
command = ["scanner-mcp", "--stdio"]
env = { SCANNER_TOKEN = "$SCANNER_TOKEN" }   # substituted from the environment at launch

[trust]
repos = ["github.com/example/project"]
ci = [ { event = "push-default-branch" } ]

[policy]
confirmation_expiry_days = 180

[remediation]
platform = "prompt"      # prompt | manual | auto
high_impact = "prompt"   # prompt | manual | auto

darnit config show prints the file in use, its SHA-256 digest, the permission-check result, and the effective settings with secrets redacted. Every audit report records the same source and digest, so reference secrets as $VAR rather than writing them into the file.

Safeguards:

  • Validation: unknown keys and invalid values stop the run with an error naming the file and key.
  • Containment: an operator configuration path inside the audited repository is refused, and the refusal is reported. A repository cannot supply operator configuration by passing a path into itself.
  • Permission check (POSIX): the file and each parent directory up to your home directory must be owned by you (or root) and not group- or world-writable. A failing file is loaded with a warning, or refused in strict mode.
  • Strict mode: enabled by --strict-operator-config, automatically in recognized CI, or by policy.strict_permissions = true in the file. The file can only turn strict mode on, never off.

Trusted Repositories and CI

A repository's claims can only be honored when the operator trusts that repository for the run.

  • Local runs: a repository is trusted when the identity you name (--repo HOST/NAMESPACE/NAME on the CLI and harness, or the owner/repo arguments of an MCP tool) is listed in [trust].repos. Identities are compared in canonical form, so SSH and HTTPS URLs, a trailing .git, and host case all match. A checkout's own remotes are never trusted; a mismatch between your target and the checkout's origin is reported.
  • CI: trust comes from CI metadata and an opt-in rule. The only rule is push-default-branch: a push to the repository's default branch (GitHub Actions or GitLab CI) of a listed repository, with the checked-out commit matching the one CI reports. Pull requests, merge requests (from forks or not), workflow_run, merge-queue events, and unrecognized CI environments are untrusted.

Manage the list with darnit config trust add|list|remove, which edits only [trust].repos in the operator configuration file. Reports record the trust decision, its reason, and the CI facts used.

Project Claims in .project/

A repository records that a control does not apply in .project/darnit.yaml:

controls:
  OSPS-BR-02.01:
    status: n/a
    reason: "Pre-1.0 project with no releases yet. Tracked in issue #123."
    asserted_by: "@maintainer"   # optional

Project data in .project/ that makes a control not applicable (for example a value its applicability condition reads) is a claim too. Every claim has one outcome, shown in the report:

Outcome When Effect
honored The repository is trusted, an explicit claim gives a reason, and no evidence the control declares contradicts it; or an operator confirmed the claim Control is N/A, labelled asserted
pending Anything else, including untrusted repositories, claims without a reason, and evidence that could not be obtained Control is evaluated normally and counts as non-compliant
contradicted Evidence contradicts the claim (for example a release exists) Claim is ignored; control is evaluated normally

An operator can confirm a pending claim through the confirm_project_data MCP tool (confirm_not_applicable). Confirmations are stored on the operator side, never in the repository, and lapse when they expire or when the claim's reason or evidence changes. An agent must only confirm a claim when the operator explicitly asks it to.

Removed: .baseline.toml

darnit no longer reads .baseline.toml. Nothing in it has any effect: not per-control status and reason (even for a trusted repository), not extends (use --framework), and not tool settings. When the file is present, the audit reports one notice saying it was ignored.

Run darnit config migrate [REPO] to write its claims to .project/darnit.yaml (existing claims are kept unless you pass --force) and print a proposed operator configuration fragment for its tool settings. The command never writes operator configuration. Review both, then delete .baseline.toml.

Configuration Review Checklist

When reviewing changes to .project/:

  1. Verify N/A justifications are legitimate and each claim has a reason
  2. Check the audit report for pending and contradicted claims, and for ignored repository settings, which indicate configuration that belongs in operator configuration

MCP Server Security

When running Darnit as an MCP server with AI assistants, consider these security aspects.

Access Control

The MCP server has access to:

  • File system (read for auditing, write for remediation)
  • GitHub API (via configured token)
  • Network (for external tool integrations)

Register darnit at User Scope

Register darnit's MCP server in your own (user-scope) agent configuration, not in a configuration file committed to a repository. darnit install writes user-scope registrations by default; --project writes a repository-scoped one and is not recommended.

A repository-scoped registration lets the repository decide how darnit is launched: its command, arguments, and environment. For example, a repository-scoped uv run darnit serve runs the repository's own copy of darnit, not the one you installed. Do not approve repository-scoped darnit servers in repositories you do not control. When darnit's own code is running from inside the audited repository, audit results include a warning recommending user-scope registration (expected only when developing darnit itself).

{
  "mcpServers": {
    "darnit": {
      "command": "darnit",
      "args": ["serve"],
      "env": {
        "GITHUB_TOKEN": "${GITHUB_TOKEN}",
        "DARNIT_LOG_LEVEL": "INFO"
      }
    }
  }
}

Pass --operator-config PATH and --strict-operator-config in args if you keep operator configuration somewhere other than the per-user location.

Security Recommendations

  1. Run with minimal permissions - Use read-only tokens when only auditing
  2. Preview, then approve by digest - Remediation previews by default; approve only the change sets and plan items a person reviewed
  3. Review AI-suggested changes - Don't blindly apply remediation recommendations
  4. Isolate sensitive repositories - Consider separate MCP server instances
  5. Monitor MCP server logs - Track what operations are being performed

Preview Mode

remediate_audit_findings, enable_branch_protection, and remediate_community_spec preview by default (dry_run=True), and darnit run previews unless given --apply. A preview writes nothing: no file, no platform setting, no run manifest. See Remediation Safety.


Plugin Security Model

Darnit's plugin system allows extending functionality through third-party packages. This section describes the security model for plugins.

Current Status

Note: The Sigstore verification module (darnit.core.verification) is fully implemented and tested, but it is not yet integrated into plugin discovery. Currently, discover_implementations() loads all entry-point plugins unconditionally. The verification infrastructure is ready to be wired in — see the TODO in packages/darnit/src/darnit/core/discovery.py.

In practice this means:

  • Local development: All plugins load without verification (expected behavior).
  • Published releases: The GitHub Actions publish workflow supports Sigstore attestations (attestations: true), but the release trigger is not yet active.
  • Production hardening: Once verification is integrated into discovery and packages are published with attestations, set allow_unsigned = false to enforce signed-only plugins.

Plugin Verification with Sigstore

Darnit supports Sigstore-based plugin verification to ensure plugins come from trusted sources.

Configuration

# Operator configuration (for example ~/.config/darnit/config.toml)
[plugins]
allow_unsigned = false          # Reject unsigned plugins (use true for local dev)
trusted_publishers = [          # Trust plugins signed by these OIDC identities
    "https://github.com/kusari-oss",
    "https://github.com/openssf",
]

Trusted Publisher Formats

The trusted_publishers list supports multiple identity formats:

Format Example Matches
Full GitHub URL https://github.com/kusari-oss Any repo in that org
GitHub org name kusari-oss Substring match in identity
Specific repo https://github.com/kusari-oss/darnit Exact repo match
Email identity security@example.com Email-based OIDC

Example with multiple formats:

[plugins]
allow_unsigned = false
trusted_publishers = [
    "https://github.com/kusari-oss",     # Trust all repos in org
    "https://github.com/openssf",         # Trust OpenSSF org
    "mycompany",                          # Trust by org name substring
]

Verification Modes

Mode allow_unsigned Behavior
Strict false Only signed plugins from trusted publishers load
Permissive true All plugins load, warnings for unsigned

Using the Verifier

from darnit.core.verification import PluginVerifier, VerificationConfig

# Production mode: require signed plugins from trusted publishers
config = VerificationConfig(
    allow_unsigned=False,
    trusted_publishers=[
        "https://github.com/kusari-oss",
        "https://github.com/openssf",
    ],
)
verifier = PluginVerifier(config)

result = verifier.verify_plugin("darnit-baseline")
if result.verified:
    if result.signed:
        print(f"Plugin verified (signed by {result.publisher})")
    else:
        print(f"Plugin allowed (unsigned): {result.warning}")
elif result.error:
    print(f"Verification failed: {result.error}")

# Development mode: allow all plugins with warnings
dev_config = VerificationConfig(allow_unsigned=True)
dev_verifier = PluginVerifier(dev_config)

Handler Registration Security

Plugins register handlers using the @register_handler decorator or register_handlers(). Registration needs no import by name. A handler referenced by module:function path instead is resolved under the policy in Dynamic Module Loading Security.

Registering Handlers

from darnit.core.handlers import register_handler

@register_handler("my_custom_check")
def my_custom_check(context):
    """Custom check implementation."""
    # Check logic here
    return PassResult(outcome=PassOutcome.PASS, ...)

The handler can then be referenced in TOML by short name:

[[controls."MY-01.01".passes]]
handler = "my_custom_check"  # Short name from registry

Security Recommendations

  1. Enable strict verification in production (allow_unsigned = false)
  2. Verify trusted publishers match expected identities
  3. Review plugin code before adding to trusted list
  4. Use short names when possible for better auditability
  5. Monitor verification cache at ~/.darnit/verification_cache/

Verification Cache

Verification results are cached to handle Sigstore service unavailability:

  • Cache location: ~/.darnit/verification_cache/
  • TTL: 24 hours by default
  • Format: JSON files keyed by package name and version

To clear the cache:

rm -rf ~/.darnit/verification_cache/

Graceful Degradation

When Sigstore services are unavailable:

  1. Cached results are used if available
  2. Warning logged if no cached result exists
  3. Behavior depends on allow_unsigned:
    • true: Plugin loads with warning
    • false: Plugin rejected

Signing Plugins with Sigstore

Plugin authors can sign their packages using Sigstore for trusted distribution.

GitHub Actions Workflow (Recommended)

The easiest way to sign plugins is via GitHub Actions with OIDC:

# .github/workflows/release.yml
name: Release

on:
  release:
    types: [published]

permissions:
  id-token: write  # Required for Sigstore OIDC
  contents: read
  attestations: write

jobs:
  publish:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - name: Set up Python
        uses: actions/setup-python@v5
        with:
          python-version: "3.12"

      - name: Install build tools
        run: pip install build twine

      - name: Build package
        run: python -m build

      - name: Publish to PyPI with attestations
        uses: pypa/gh-action-pypi-publish@release/v1
        with:
          attestations: true

Manual Signing

For local signing:

# Install sigstore
pip install sigstore

# Sign a distribution file
python -m sigstore sign dist/my_plugin-1.0.0-py3-none-any.whl

# This creates:
# - dist/my_plugin-1.0.0-py3-none-any.whl.sigstore

Verification by Users

Users can verify signed plugins:

python -m sigstore verify identity \
  --cert-identity your-email@example.com \
  --cert-oidc-issuer https://github.com/login/oauth \
  dist/my_plugin-1.0.0-py3-none-any.whl

Arbitrary Code Execution Warning

⚠️ Security Warning: Plugins can execute arbitrary code in your environment.

Darnit plugins have full Python execution capabilities and can:

  • Read and write files on your filesystem
  • Make network requests to any host
  • Execute system commands via subprocess
  • Access environment variables including secrets

Before installing any plugin:

  1. Review the source code or trust the publisher
  2. Check the publisher identity via Sigstore signature
  3. Use allow_unsigned = false to require signed plugins
  4. Run in isolated environments (containers, VMs) for untrusted plugins

For plugin authors:

  • Follow secure coding practices (input validation, no shell injection)
  • Sign your releases with Sigstore
  • Document required permissions clearly
  • Avoid hardcoded secrets or credentials

Result Integrity

A compliance tool that reports PASS on weak evidence is worse than one that reports nothing. Darnit limits who may conclude what, separates "the project fails" from "we could not measure", and never lets a model decide a PASS on its own. The authoritative rules are in framework-design.md sections 3.0.1, 3.0.2, 3.5, 3.8, and 5.2.

Per-Step Conclusions

Each control is verified by an ordered list of steps. Every step type has a ceiling: the outcomes it may at most conclude for its control.

Step type May conclude
file_exists, regex / pattern FAIL only (absence is proof; presence of a file or keyword is not). PASS only when the step declares existence = true because the requirement is literally that the file exists.
exec, gh_api, github_branch_protection PASS or FAIL
llm_eval, manual Nothing
Plugin handlers What they register (ceiling=...); nothing if they register no ceiling

A step may narrow its ceiling with concludes, but may widen it only with a recorded promotion that cites a measurement on the adversarial fixture corpus (tests/darnit_baseline/corpus/); a widening without one is rejected when controls load. An outcome a step may not conclude is kept as evidence and evaluation continues. A pattern miss is inconclusive unless the step declares fail_on_miss. When no step concludes, the control is WARN (needs verification).

When reviewing a framework TOML or plugin change, treat any new existence = true, promotion, fail_on_miss, fail_on_status, or plugin ceiling as a change to what darnit is willing to claim, and check it against the corpus report (uv run python scripts/corpus_report.py --format markdown). CI fails on any false PASS by a step allowed to conclude PASS.

ERROR Is Never FAIL

A step that could not measure returns ERROR with a class and cause: auth (401/403), rate_limit (429 or a rate-limit 403), unavailable (5xx, transport failure, undeclared status), missing_tool (an absent binary or required MCP server), or evaluation. ERROR never concludes FAIL: later steps still run, and if none concludes the control ends ERROR. A platform response proves failure only when the gh_api step lists its status in fail_on_status (for example 404 for "no branch protection"), and a rate limit never does. A token that cannot read a setting therefore shows up as ERROR [auth], not as a failing project. ERROR is non-compliant.

PASS Candidates Confirmed by the Operator

Controls that need judgment of document content end PENDING (pending.kind = "llm_judgment") after the deterministic steps. A judgment comes from the harness's model step or from a coding agent through the submit_judgment MCP tool; both follow the same rules:

  • A positive judgment must cite verbatim excerpts of the content the step read. If every excerpt is found, it becomes a PASS candidate (PENDING, pending.kind = "confirmation"), stored on the operator side and labelled with the model, version, and a digest of the judged content and rubric. A candidate is not compliant.
  • A judgment that cites text not present in the content produces no candidate and the control stays WARN.
  • A negative judgment is a model finding: FAIL with authority: suggestive and concluded_by: llm_judgment.
  • A model-service failure is ERROR.

Only an operator makes a candidate count, through confirm_project_data (confirm_pass_candidate). The confirmed control then reports PASS with authority: asserted, concluded_by: confirmation, and the confirmer, time, and expiry. The confirmation lapses when the judged content or the rubric changes or it expires. Agents must never confirm a candidate without the operator's explicit instruction, and the ActionPlan audit step accepts no client-supplied results. Reports and attestations keep a candidate's status PENDING and label it "not compliant until confirmed".


Attestation Security

Darnit can generate cryptographically signed attestations for compliance status.

Sigstore Integration

Attestations are signed using Sigstore for keyless signing:

  • No key management required
  • Transparency log provides tamper evidence
  • OIDC identity ties signatures to verifiable identities

Verification

To verify an attestation:

# Install cosign
brew install cosign

# Verify the attestation
cosign verify-attestation \
  --type https://in-toto.io/Statement/v1 \
  --certificate-identity-regexp '.*' \
  --certificate-oidc-issuer-regexp '.*' \
  attestation.json

Attestation Security Considerations

Aspect Recommendation
Storage Store attestations separately from code
Retention Keep attestations for audit trail
Verification Verify attestations in CI/CD pipelines
Trust Configure allowed OIDC issuers for your organization

Remediation Security

Remediation changes files in your repository, .project/ data, commits and pull requests, and settings on the hosting platform. A damaging change is worse than no change, so remediation plans before it acts, acts only on what it planned, and reports only what it verified. The authoritative rules are in docs/architecture/framework-design.md sections 4 and 15.

Remediation Safety

Preview equals apply. Every remediation previews by default. The preview runs the same handler logic as the apply against the current state and lists every file to be created or changed, every platform field with its value before and after, every command, and a digest for each plan item and platform change set. A step whose effect cannot be computed in advance (a handler without plan support, or an exec step not declared effects = "working_tree" and offline = true) is labelled "cannot be previewed exactly".

Platform changes never weaken settings. One platform engine makes every platform write, from TOML (platform_setting) and from enable_branch_protection alike. It:

  • reads the current settings first, and writes nothing if they cannot be read;
  • changes only what the control requires, and never removes, loosens, or resets anything else (required approvals are a minimum; existing status checks, push restrictions, code-owner review, and linear history stay as they are);
  • writes nothing when the settings, or an active repository or organization ruleset, already satisfy the control;
  • targets the repository's default branch unless a branch is named;
  • reads the settings back afterwards and derives the outcome from them, not from response text.

Approval is bound to the change. The operator configuration sets the policy separately for platform changes and for high-impact changes (repository visibility, organization-wide settings):

Policy Behavior
prompt (default) Writes a change set only when its digest is approved. darnit run asks on the terminal; through MCP, the agent passes approve with the digests the person approved
manual Makes no platform change and reports the steps
auto Writes without asking, still reading first, changing only what is needed, and reading back; the report records the change and its impact
  • The policy comes only from operator configuration; a [remediation] setting in the audited repository is ignored.
  • A digest covers the change and the settings it was computed from. If the settings changed after the preview, nothing is written and a new preview is needed.
  • A high-impact change set under prompt needs its own digest; a batch approval never covers it.
  • dry_run=False alone approves nothing. A remediation marked safe = false and a step that cannot be previewed exactly need their own plan item digest under every policy, including auto.
  • Organization two-factor enforcement has no API, so its remediation is manual under every policy.

Outcomes come from a re-check. Each control gets one outcome (fixed, changed_not_passing, changed_not_verified, unchanged, needs_approval, needs_confirmation, manual, error). fixed needs a change and a passing re-check of the control. Summaries and the commit and pull request steps are derived from these outcomes, never from text in the report. If darnit cannot tell whether project context is still unconfirmed, remediation does not run.

Version-Control Safety

  • Your work is never committed. Each apply records the files it wrote in an operator-side run manifest (never inside the checkout). commit_remediation_changes stages only those files, and only while they are unchanged since remediation wrote them. Ignored files are never staged, and there is no option to stage everything.
  • No stash. darnit never stashes, drops a stash, or discards your changes. A new branch keeps your uncommitted changes in the working tree; switching to an existing branch requires a clean tree.
  • Unsafe states stop before any change: a detached HEAD, a merge or rebase in progress, or a remediation branch holding commits without the Darnit-Remediation-Run trailer.
  • Your edits are not overwritten. A file with uncommitted changes is not written; the preview and the apply both report it as user_changes_present.
  • create_remediation_pr pushes only the remediation branch.

Using MCP Tools Safely

# 1. Preview (the default): planned files, platform changes, and digests
remediate_audit_findings(local_path="/path/to/repo", categories=["all"])

# 2. Show the preview to the person. Apply with only the digests they approved,
#    on a branch, and open a pull request.
remediate_audit_findings(
    local_path="/path/to/repo",
    categories=["all"],
    dry_run=False,
    approve=["sha256:..."],
    branch_name="fix/openssf-baseline-compliance",
    auto_commit=True,
    create_pr=True,
)

# 3. Review the pull request before merging.

Never pass digests the person did not approve, and never use dry_run=False as a substitute for approval.


Reporting Security Issues

If you discover a security vulnerability in Darnit:

  1. DO NOT create a public GitHub issue
  2. See SECURITY.md for reporting instructions
  3. Email security concerns to the maintainers listed there

Additional Resources