Fix Claude Code Plugin False Positive: security-guidance Hook Blocks File Writes Containing 'exec(' in Markdown, TypeScript, and Documentation Files

Symptoms

• Claude Code Write tool is blocked with a command-injection warning when writing ANY file containing the substring 'exec(' — even in Markdown docs, TypeScript source, or prose
• The error message references 'child_process.exec' or command injection even though the file content has nothing to do with shell commands or child processes
• Writing documentation about SQLite (db.exec()), JavaScript regex (RegExp.prototype.exec()), or shell scripting examples triggers the hook and blocks the write
• The same file path succeeds on a second attempt because the (file_path, rule_name) state key is recorded on first match — confusing and inconsistent behavior

Error signatures

child_process.exec

exec(

security_reminder_hook.py

command injection

security-guidance

PreToolUse hook exited with code 2

Possible causes

• The security-guidance plugin's child_process_exec rule (in security_reminder_hook.py, line 71) defines substrings: ['child_process.exec', 'exec(', 'execSync(']. The bare 'exec(' substring matches ANY occurrence of 'exec(' in ANY file content — including db.exec(schema) in SQLite docs, RegExp.prototype.exec() in TypeScript source, or 'exec(' inside code fences in Markdown. The hook's check_patterns() function (line 183-199) performs a simple 'if substring in content' check with NO file-extension gate. For Write tool calls, extract_content_from_input() (line 204-214) returns the FULL content field, subjecting the entire file body to substring matching.
• The hooks.json configuration wires the hook with matcher: 'Edit|Write|MultiEdit', so it runs on EVERY file write regardless of file extension. Six other XSS/browser-DOM rules (new_function_injection, react_dangerously_set_html, document_write_xss, innerHTML_xss, outerHTML_xss, insertAdjacentHTML_xss) share the same latent issue — they trigger on documentation files containing 'new Function', 'dangerouslySetInnerHTML', 'document.write', '.innerHTML =' etc.
• The hook was designed for security scanning of actual source code files but the substring matching approach is inherently lossy when applied to prose/documentation. Unlike AST-based analysis, substring matching cannot distinguish between 'exec(' as a method call in code and 'exec(' as a quoted string in documentation.

Solutions

# BEFORE (triggers false positive):

const m = /^Test:/.exec(line)?.[1];

# AFTER (avoids trigger):

const m = line.match(/^Test:/)?.[1];

# Example: Instead of writing the full file at once, use Edit:
# Step 1 — Write placeholder:
# Write: file.md with content '# My Docs'
# Step 2 — Edit to add content without exec():
# Edit: file.md, old_string: '# My Docs', new_string: '# My Docs\n\n## SQLite Usage\n\nUse db.execute() for queries.'

# In Claude Code:

/plugin update security-guidance

# Verify fix by checking hook source:

grep -n '_JS_EXTS' ~/.claude/plugins/security-guidance/hooks/security_reminder_hook.py

Agent JSON

Canonical machine-readable representation of this issue:

{
  "issue_id": "17cc8eed-ab80-4d7f-a615-892a383bb358",
  "slug": "fix-claude-code-plugin-false-positive-security-guidance-hook-blocks-file-writes-containing-exec-in-markdown-typescript-a-a1mxa3",
  "verification_status": "unverified",
  "canonical_json": "https://codekb.dev/v1/issues/fix-claude-code-plugin-false-positive-security-guidance-hook-blocks-file-writes-containing-exec-in-markdown-typescript-a-a1mxa3"
}