voyage/hooks/scripts/pre-bash-executor.mjs

#!/usr/bin/env node
// Hook: pre-bash-executor.mjs
// Event: PreToolUse (Bash)
// Purpose: Block or warn about destructive shell commands, and ask a person
//   before merge into main, push, tag/release and destructive git (P12).
//   Wired universally (every Voyage session, not just execution) by deliberate
//   decision -- these are session-agnostic safety rails (rm -rf /, fork bombs,
//   ...). The CC if: path-scoping mechanism now works, but narrowing to
//   execute-only would only weaken protection with no offsetting benefit. See
//   cc-upgrade matrix CC-15/F2.
//
// Precondition: Voyage's guards are deterministic only when no installed mod
//   handles `tool.check`. A mod that does answers after the PreToolUse hooks
//   and can replace their answer (code.claude.com/docs/en/permissions section Extend
//   permissions with hooks). A hook cannot see whether such a mod is installed.
//
// Protocol:
//   - Read JSON from stdin: { tool_name, tool_input, cwd }
//   - tool_input.command — the shell command string
//   - BLOCK (exit 2): catastrophic/irreversible operations
//   - ASK   (exit 0, JSON permissionDecision "ask"): merge into main, push,
//     tag/release, destructive git (hooks/lib/git-approval.mjs). The prompt is
//     labelled [plugin:voyage] and also appears in auto mode (hooks reference
//     section PreToolUse decision control). Advisories are added to the prompt.
//   - WARN  (exit 0): risky but recoverable operations — advisory to stderr
//   - Allow (exit 0): everything else
//
// Based on llm-security's pre-bash-destructive.mjs with executor-specific additions.
// Command reading lives in hooks/lib/bash-view.mjs (shared with the hook that
// logs approvals).

import { readFileSync } from 'node:fs';

// The guard's own modules are loaded so that a broken install cannot crash
// the hook: a crash (exit 1) is a non-blocking error to Claude Code, which
// would let every command through. A module that will not load makes the
// guard ask about every command instead.
let lib;
let loadError = null;
try {
  const [view, approval, record] = await Promise.all([
    import('../lib/bash-view.mjs'),
    import('../lib/git-approval.mjs'),
    import('../lib/approval-record.mjs'),
  ]);
  lib = { ...view, ...approval, ...record };
} catch (e) {
  loadError = e;
}

// ---------------------------------------------------------------------------
// BLOCK rules — exit 2, command is not executed.
// ---------------------------------------------------------------------------
const BLOCK_RULES = [
  {
    name: 'Filesystem root/home destruction (rm -rf /)',
    // Matches rm with both -r and -f flags targeting /, ~, or $HOME.
    // Uses (?:\s|$) instead of \b because / and ~ are non-word chars.
    pattern: /\brm\s+(?:-[a-zA-Z]*f[a-zA-Z]*\s+|--force\s+)*-[a-zA-Z]*r[a-zA-Z]*\s+(?:\/|~|\$HOME)(?:\s|$)/,
    description:
      '`rm -rf /`, `rm -rf ~`, and `rm -rf $HOME` would destroy the filesystem ' +
      'or home directory. Unconditionally blocked.',
  },
  {
    name: 'World-writable chmod (chmod 777)',
    pattern: /\bchmod\s+(?:-[a-zA-Z]+\s+)*777\b/,
    description:
      '`chmod 777` grants full read/write/execute to all users. ' +
      'Use minimal permissions (e.g. 644, 755).',
  },
  {
    name: 'Pipe-to-shell (curl|bash, wget|sh)',
    pattern: /(?:curl|wget)\b[^|]*\|\s*(?:bash|sh|zsh|ksh|dash)\b/,
    description:
      'Piping remote content into a shell allows arbitrary remote code execution. ' +
      'Download first, review, then execute.',
  },
  {
    name: 'Fork bomb',
    pattern: /:\(\)\s*\{\s*:\s*\|\s*:&\s*\}\s*;?\s*:/,
    description: 'Fork bomb — exhausts system process resources. Blocked.',
  },
  {
    name: 'Filesystem format (mkfs)',
    pattern: /\bmkfs(?:\.[a-z0-9]+)?\s/,
    description: '`mkfs` formats a filesystem, destroying all data. Blocked.',
  },
  {
    name: 'Raw disk overwrite via dd',
    pattern: /\bdd\b[^&|;]*\bof=\/dev\/(?:sd|nvme|hd|vd|xvd|mmcblk)[a-z0-9]*/,
    description: '`dd` writing to a raw block device destroys disk data. Blocked.',
  },
  {
    name: 'Direct device write (> /dev/sd*)',
    pattern: />\s*\/dev\/(?:sd|nvme|hd|vd|xvd|mmcblk)[a-z0-9]*/,
    description: 'Shell redirection to a block device destroys disk data. Blocked.',
  },
  {
    name: 'eval with variable/command expansion',
    pattern: /\beval\s+(?:`|\$[\({]|"[^"]*\$)/,
    description:
      '`eval` with variable or command substitution is a code injection vector. ' +
      'Refactor to use explicit commands.',
  },
  // --- Executor-specific additions ---
  {
    name: 'System shutdown/reboot',
    // Anchored to command position — start of string/line, or after a
    // separator (`;`, `|`, `&`, `&&`), with optional `sudo` and an optional
    // absolute path. An unanchored \b match blocked the bare word anywhere,
    // including quoted grep patterns, heredoc data, and commit messages.
    //
    // Runs against commandView, not the whitespace-collapsed string: collapsing
    // \s+ to ' ' would erase the newline separator before the pattern ever saw
    // it, and quoted spans must read as data, not as command position.
    commandView: true,
    pattern: /(?:^|[\n;|&])\s*(?:sudo\s+(?:-[a-zA-Z]+\s+)*)?(?:[\w./-]*\/)?(?:shutdown|reboot|halt|poweroff)\b/,
    description: 'System shutdown/reboot commands are blocked during execution.',
  },
  {
    name: 'Cron persistence',
    pattern: /\bcrontab\b|>\s*\/etc\/cron/,
    description:
      'Writing to crontab or /etc/cron* creates persistent scheduled tasks. ' +
      'Blocked during execution.',
  },
  {
    name: 'Base64-encoded execution',
    pattern: /\bbase64\b[^|]*\|\s*(?:bash|sh|zsh)\b/,
    description: 'Base64-decoded content piped to shell is obfuscated code execution. Blocked.',
  },
  {
    name: 'Kill all processes (kill -9 -1)',
    pattern: /\b(?:kill|pkill)\s+-9\s+-1\b/,
    description: 'Killing all user processes with signal 9. Blocked.',
  },
  {
    name: 'History destruction',
    pattern: /\bhistory\s+-c\b|>\s*~\/\.bash_history\b|>\s*~\/\.zsh_history\b/,
    description: 'Clearing shell history or truncating history files. Blocked.',
  },
];

// ---------------------------------------------------------------------------
// WARN rules — exit 0 with advisory message on stderr.
// ---------------------------------------------------------------------------
const WARN_RULES = [
  {
    name: 'Force push (git push --force)',
    pattern: /\bgit\s+push\b[^|&;]*(?:--force|-f)\b/,
    description:
      'WARNING: `git push --force` rewrites remote history. Prefer `--force-with-lease`.',
  },
  {
    name: 'Hard reset (git reset --hard)',
    pattern: /\bgit\s+reset\s+--hard\b/,
    description:
      'WARNING: `git reset --hard` permanently discards uncommitted changes.',
  },
  {
    name: 'Recursive remove (rm -rf, non-root)',
    pattern: /\brm\s+(?:-[a-zA-Z]*f[a-zA-Z]*\s+|--force\s+)*-[a-zA-Z]*r[a-zA-Z]*\s+/,
    description:
      'WARNING: `rm -rf` permanently deletes files. Verify the target path.',
  },
  {
    name: 'Docker system prune',
    pattern: /\bdocker\s+system\s+prune\b/,
    description:
      'WARNING: `docker system prune` removes all stopped containers and unused images.',
  },
  {
    name: 'npm publish',
    pattern: /\bnpm\s+publish\b/,
    description:
      'WARNING: `npm publish` releases a package to the public registry.',
  },
  {
    name: 'DROP TABLE or DROP DATABASE (SQL)',
    pattern: /\bDROP\s+(?:TABLE|DATABASE|SCHEMA)\b/i,
    description:
      'WARNING: SQL DROP permanently deletes database objects.',
  },
  {
    name: 'DELETE without WHERE (SQL)',
    pattern: /\bDELETE\s+FROM\s+\w+(?:\s*;|\s*$)/i,
    description:
      'WARNING: DELETE FROM without WHERE deletes all rows.',
  },
  // --- Executor-specific additions ---
  {
    name: 'Dependency installation during execution',
    pattern: /\b(?:npm\s+install\s+--save|pip3?\s+install\s+(?!-e\s+\.)|cargo\s+add)\b/,
    description:
      'WARNING: Installing dependencies during plan execution is unusual. ' +
      'Verify this is intentional.',
  },
];

// ---------------------------------------------------------------------------
// Main
// ---------------------------------------------------------------------------
let input;
try {
  const raw = readFileSync(0, 'utf-8');
  input = JSON.parse(raw);
} catch {
  // Cannot parse stdin — fail open.
  process.exit(0);
}

const command = input?.tool_input?.command;

if (!command || typeof command !== 'string') {
  process.exit(0);
}

if (loadError) {
  process.stdout.write(JSON.stringify({
    hookSpecificOutput: {
      hookEventName: 'PreToolUse',
      permissionDecision: 'ask',
      permissionDecisionReason:
        `Voyage's Bash guard could not load its rules (${loadError.message}), so this command was not checked. ` +
        'Way forward: approve only a command you have read yourself; reinstall Voyage to restore the guard.',
    },
  }));
  process.exit(0);
}
const { normalizeBashExpansion, normalizeCommand, commandPositionView, classifyGitApproval, askReason, writeApprovalRecord } = lib;

// Strip bash evasion, then normalize whitespace
const deobfuscated = normalizeBashExpansion(command);
const normalized = normalizeCommand(deobfuscated);
const commandView = commandPositionView(deobfuscated.replace(/\x1B\[[0-9;]*m/g, ''));

// Check BLOCK rules first
for (const rule of BLOCK_RULES) {
  if (rule.pattern.test(rule.commandView ? commandView : normalized)) {
    process.stderr.write(
      `[voyage] BLOCKED: ${rule.name}\n` +
      `  Command: ${normalized.slice(0, 200)}${normalized.length > 200 ? '...' : ''}\n` +
      `  ${rule.description}\n`
    );
    process.exit(2);
  }
}

// Check WARN rules (advisory — still exit 0)
const warnings = [];
for (const rule of WARN_RULES) {
  if (rule.pattern.test(normalized)) {
    warnings.push(`  [WARN] ${rule.name}: ${rule.description}`);
  }
}

if (warnings.length > 0) {
  process.stderr.write(
    `[voyage] SECURITY ADVISORY: Potentially risky command.\n` +
    `  Command: ${normalized.slice(0, 200)}${normalized.length > 200 ? '...' : ''}\n` +
    warnings.join('\n') + '\n'
  );
}

// P12: ask a person before merge into main, push, tag/release, destructive git.
// A classifier error must not turn into a silent allow of a push: ask instead.
let approvals;
try {
  approvals = classifyGitApproval(command, { cwd: input.cwd });
} catch (e) {
  approvals = [{ name: `a command the approval guard could not read (${e.message})`, kind: null, way: 'approve only if you have read the command yourself.' }];
}

if (approvals.length > 0) {
  // What the person is asked is what post-approval-log.mjs logs once the call ran.
  const loggable = approvals.filter((m) => m.kind).map(({ kind, name, subject }) => ({ kind, name, subject }));
  const recorded = writeApprovalRecord(input.session_id, input.tool_use_id, {
    command,
    permission_mode: input.permission_mode ?? null,
    matches: loggable,
    asked_at: new Date().toISOString(),
  });
  // Say it now if this approval cannot reach the log afterwards.
  const unlogged = loggable.length > 0 && !recorded
    ? ' Note: this approval will not be logged (Voyage could not record the question).' : '';
  const advisory = (warnings.length > 0 ? ` Advisory: ${warnings.map((w) => w.trim()).join(' ')}` : '') + unlogged;
  process.stdout.write(JSON.stringify({
    hookSpecificOutput: {
      hookEventName: 'PreToolUse',
      permissionDecision: 'ask',
      permissionDecisionReason: askReason(approvals) + advisory,
    },
  }));
}

process.exit(0);