id: ruby-unsafe-regex
name: Unsafe Dynamic Regex
severity: warning
category: security
defect_class: injection
inline_tier: blocking
language: ruby

message: "Regexp.new with variable — ReDoS risk if pattern is user-controlled"

description: |
  Building regexes from variables can cause ReDoS if user-controlled.
  A crafted pattern causes catastrophic backtracking.
  
  ✅ FIX:
    safe = Regexp.escape(user_input)
    Regexp.new(safe)
    
    # Or use string methods:
    content.include?(user_input)

query: |
  (call
    receiver: (constant) @RECV
    method: (identifier) @METH
    arguments: (argument_list
      (identifier) @PATTERN)
    (#eq? @RECV "Regexp")
    (#eq? @METH "new"))

metavars:
  - RECV
  - METH
  - PATTERN

has_fix: false

tags:
  - security
  - regex
  - redos

examples:
  bad: |
    pattern = params[:filter]
    Regexp.new(pattern)          # ReDoS risk!
    Regexp.new(user_input, 'i')  # ReDoS risk!
  
  good: |
    safe = Regexp.escape(params[:filter])
    Regexp.new(safe)