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. 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.
//
// Protocol:
//   - Read JSON from stdin: { tool_name, tool_input }
//   - tool_input.command — the shell command string
//   - BLOCK (exit 2): catastrophic/irreversible operations
//   - 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.
// bash-normalize logic copied inline (MIT) — cannot import from separate plugin.

import { readFileSync } from 'node:fs';

// ---------------------------------------------------------------------------
// Bash normalization (from llm-security/scanners/lib/bash-normalize.mjs)
// Strips bash evasion techniques: empty quotes, ${} expansion, backslash splitting.
// ---------------------------------------------------------------------------
function normalizeBashExpansion(cmd) {
  if (!cmd || typeof cmd !== 'string') return cmd || '';

  let result = cmd
    // Strip empty single quotes: w''get -> wget
    .replace(/''/g, '')
    // Strip empty double quotes: r""m -> rm
    .replace(/""/g, '')
    // Single-char ${x} -> x (evasion: c${u}rl -> curl, assumes x=x)
    .replace(/\$\{(\w)\}/g, '$1')
    // Multi-char ${ANYTHING} -> '' (unknown value, strip entirely)
    .replace(/\$\{[^}]*\}/g, '')
    // Strip backtick subshell with empty/whitespace content
    .replace(/`\s*`/g, '');

  // Iteratively strip backslash between word chars (c\u\r\l needs 2 passes)
  let prev;
  do {
    prev = result;
    result = result.replace(/(\w)\\(\w)/g, '$1$2');
  } while (result !== prev);

  return result;
}

// ---------------------------------------------------------------------------
// 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',
    pattern: /\b(?: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.',
  },
];

// ---------------------------------------------------------------------------
// Normalize: strip ANSI, collapse whitespace
// ---------------------------------------------------------------------------
function normalizeCommand(cmd) {
  return cmd
    .replace(/\x1B\[[0-9;]*m/g, '')
    .replace(/\s+/g, ' ')
    .trim();
}

// ---------------------------------------------------------------------------
// 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);
}

// Strip bash evasion, then normalize whitespace
const deobfuscated = normalizeBashExpansion(command);
const normalized = normalizeCommand(deobfuscated);

// Check BLOCK rules first
for (const rule of BLOCK_RULES) {
  if (rule.pattern.test(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'
  );
}

process.exit(0);