git-hardening/README.md

# 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

```bash
# 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

```bash
# 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