feat: initial companion repo for CC-024 Hooks

hooks/pre-tool-use.sh

@@ -0,0 +1,72 @@
+#!/bin/bash
+# pre-tool-use.sh: Block dangerous shell commands before Claude executes them.
+#
+# Claude Code calls this script BEFORE executing any Bash command.
+# The script receives a JSON object on stdin with two fields:
+#   - tool_name: the name of the tool being called (e.g., "Bash")
+#   - tool_input: the arguments passed to the tool (e.g., {"command": "ls -la"})
+#
+# Exit codes:
+#   0  Allow the command to proceed
+#   2  Block the command (Claude receives the "reason" field as an error message)
+#
+# When blocking, write a JSON object to stdout:
+#   {"decision": "block", "reason": "Human-readable explanation"}
+#
+# Make this script executable: chmod +x hooks/pre-tool-use.sh
+
+# Read the full JSON payload from stdin
+input=$(cat)
+
+# Extract tool_name and the command argument from the JSON
+tool_name=$(echo "$input" | python3 -c "import sys,json; print(json.load(sys.stdin).get('tool_name',''))" 2>/dev/null)
+command=$(echo "$input" | python3 -c "import sys,json; print(json.load(sys.stdin).get('tool_input',{}).get('command',''))" 2>/dev/null)
+
+# Only inspect Bash tool calls. Allow everything else immediately.
+if [ "$tool_name" != "Bash" ]; then
+  exit 0
+fi
+
+# Each blocked pattern is checked separately with a descriptive reason.
+# Pattern matching uses grep -qiE (case-insensitive extended regex).
+
+block_if_match() {
+  local pattern="$1"
+  local reason="$2"
+  if echo "$command" | grep -qiE "$pattern"; then
+    echo "{\"decision\": \"block\", \"reason\": \"$reason\"}"
+    exit 2
+  fi
+}
+
+# Recursive deletion of the root filesystem
+block_if_match 'rm -rf /' 'Recursive deletion from root is not allowed'
+
+# sudo: prevents privilege escalation
+block_if_match 'sudo ' 'Commands with sudo are not allowed'
+
+# World-writable permissions: a common misconfiguration that opens security holes
+block_if_match 'chmod 777' 'chmod 777 is not allowed: use more restrictive permissions'
+
+# Direct disk write: can wipe an entire disk in seconds
+block_if_match 'dd if=' 'Direct disk writes with dd are not allowed'
+
+# Filesystem formatting: permanently destroys data
+block_if_match 'mkfs' 'Formatting filesystems is not allowed'
+
+# Fork bomb: crashes the system by spawning processes until resources are exhausted
+block_if_match ':\(\)\{' 'Fork bombs are not allowed'
+
+# Piping curl or wget output directly into a shell:
+# executes arbitrary remote code without review
+block_if_match 'curl.+\|.+bash' 'Piping curl into bash is not allowed'
+block_if_match 'curl.+\|.+sh' 'Piping curl output into a shell is not allowed'
+block_if_match 'wget.+\|.+bash' 'Piping wget into bash is not allowed'
+block_if_match 'wget.+\|.+sh' 'Piping wget output into a shell is not allowed'
+
+# Shutdown and reboot: should never be triggered by an automated agent
+block_if_match '^shutdown' 'Shutdown commands are not allowed'
+block_if_match '^reboot' 'Reboot commands are not allowed'
+
+# Nothing matched: allow the command
+exit 0