git-harden.sh

Audit and harden your global git configuration with security-focused defaults.

Protects against history rewriting, supply chain attacks, credential theft, and malicious repository exploitation. Runs on macOS and Linux.

Quick Start

# Clone and run
git clone https://github.com/YOUR_ORG/git-hardening.git
cd git-hardening
chmod +x git-harden.sh

# Audit your current config (no changes)
./git-harden.sh --audit

# Interactive mode — review and approve each change
./git-harden.sh

# Apply all recommended defaults without prompting
./git-harden.sh -y

On first interactive run, the script asks you to confirm you've reviewed it for safety. If you haven't, it prints instructions for piping it to Claude Code or Gemini CLI for an automated review.

What It Does

The script runs in two phases:

1. Audit — scans your current git config --global and ~/.ssh/config, prints a color-coded report:
   • [OK] already set to the recommended value
   • [WARN] set to a non-recommended value
   • [MISS] not configured
2. Apply — for each non-OK setting, shows what it does and prompts you to accept or skip (or auto-applies with -y)

Settings Applied

Category	What it does
Object integrity	Validates all objects on fetch/push/receive (transfer.fsckObjects, etc.)
Protocol restrictions	Default-deny policy: only HTTPS and SSH allowed. Blocks git:// (unencrypted) and ext:// (arbitrary command execution)
Filesystem protection	Enables core.protectNTFS, core.protectHFS, disables core.fsmonitor
Hook control	Redirects core.hooksPath to ~/.config/git/hooks so repo-local hooks can't execute
Repository safety	safe.bareRepository=explicit, submodule.recurse=false
Pull/merge hardening	pull.ff=only, merge.ff=only — refuses non-fast-forward merges, surfacing rewritten history
Transport security	Rewrites http:// to https://, enforces http.sslVerify=true
Credential storage	Platform-detected secure helper (osxkeychain on macOS, libsecret on Linux). Warns if using plaintext store
Commit signing	SSH-based signing with interactive key setup wizard (software or FIDO2 hardware key)
SSH hardening	StrictHostKeyChecking=accept-new, HashKnownHosts=yes, IdentitiesOnly=yes, modern algorithm restrictions
Visibility	log.showSignature=true

A config backup is saved to ~/.config/git/pre-harden-backup-<timestamp>.txt before any changes.

Signing Setup

The script includes an interactive wizard that:

1. Detects existing SSH keys (including custom-named keys from ~/.ssh/config)
2. Detects FIDO2 hardware (YubiKey, etc.)
3. Offers two tiers:
   • Software SSH key — use existing ed25519 or generate one
   • FIDO2 hardware key — generate ed25519-sk with touch-to-sign (if hardware detected)
4. Configures user.signingkey, commit.gpgsign, tag.gpgsign
5. Sets up ~/.config/git/allowed_signers for local signature verification

With -y, the script auto-detects the best available key. If no key exists, signing config is prepared but not enabled (to avoid breaking commits).

Privacy note: The signing wizard warns that reusing the same signing key across personal and work accounts enables cross-platform identity correlation (OSINT risk). For identity separation, generate dedicated keys per context and use git's includeIf for per-org config.

Usage

git-harden.sh [OPTIONS]

Options:
  --audit       Audit only, no changes (exit code 2 if issues found)
  -y, --yes     Auto-apply all recommended defaults
  --help, -h    Show help
  --version     Show version

Exit Codes

Code	Meaning
0	All OK, or changes applied successfully
1	Error (missing dependencies, etc.)
2	Audit found issues (--audit mode)

Requirements

• git >= 2.34.0 (required for SSH signing)
• ssh-keygen
• Bash 3.2+ (compatible with macOS default bash)

Optional:

• ykman or fido2-token for FIDO2 hardware key detection

Threat Model

What this protects against

• History rewriting — pull.ff=only and merge.ff=only refuse non-fast-forward operations, making force-pushed changes visible
• Object injection — fsckObjects validates every object transferred, catching corruption or malicious payloads
• Protocol downgrade — blocks plaintext git:// and dangerous ext:// protocol
• Hook-based RCE — redirects hook execution away from repo-local .git/hooks/
• Submodule attacks — disables auto-recursion; submodules must be explicitly initialized
• Credential theft — ensures secure credential storage, warns about plaintext store
• Commit impersonation — SSH signing proves key possession (anyone can fake user.name/user.email)
• Filesystem tricks — blocks NTFS/HFS+ path manipulation attacks

What this does NOT protect against

• A compromised machine (malware can use cached keys)
• Malicious code from an authorized signer
• Historical unsigned commits (signing is not retroactive)
• Server-side misconfigurations (see admin recommendations printed by the script)

Admin Recommendations

The script prints (but does not apply) server/org-level recommendations:

• Enable "require signed commits" on protected branches
• Enable GitHub/GitLab vigilant mode
• Restrict force-pushes server-side
• Use fine-grained, short-lived tokens in CI/CD
• Maintain an allowed signers file in repos
• Clone untrusted repos with --no-recurse-submodules
• Use separate signing keys per org to prevent cross-platform identity correlation (OSINT)

Running Tests

# Run the BATS test suite (64 tests)
./test/run.sh

# Requires bats-core submodules — init them if needed
git submodule update --init --recursive

Tests run in an isolated $HOME (via mktemp) and never touch your real git or SSH config.

License

MIT