Overview
CVE-2006-4111 describes a vulnerability in Ruby on Rails before 1.1.5 where a remote attacker could cause arbitrary Ruby code execution by exploiting a File Upload request that manipulates the Ruby $LOAD_PATH via an HTTP header. In effect, an attacker could influence what the app loads at runtime, allowing code execution with the server's privileges if the application loads a library from a path supplied by the attacker.
In practice, an attacker would send a crafted file upload request including a malicious HTTP header designed to modify the LOAD_PATH, causing subsequent dynamic requires to pull code from an attacker-controlled location. The vulnerability is distinct from other Rails CVEs such as CVE-2006-4112 and centers on load path manipulation rather than input validation alone. If exploitation succeeds, this could lead to full compromise of the Rails process.
Remediation involves upgrading Rails to a patched version (1.1.5 or later) and ensuring that the app never uses user-supplied headers or file uploads to alter Ruby's load path. Adopt explicit, fixed requires and robust input validation for file uploads, and exercise least privilege for the Rails process.
Affected Versions
Rails <= 1.1.4
Code Fix Example
Ruby on Rails API Security Remediation
VULNERABLE:
# app/controllers/uploads_controller.rb
class UploadsController < ApplicationController
def create
# Attacker can influence LOAD_PATH via HTTP header on a file upload request
header_path = request.headers['HTTP_LOAD_PATH']
$LOAD_PATH.unshift header_path if header_path && !header_path.empty?
# This can cause require to load attacker-controlled code
require 'daily_vendor_library'
# ... rest of processing
end
end
FIXED:
# app/controllers/uploads_controller.rb
class UploadsController < ApplicationController
def create
# Do not allow user input to modify Ruby's load path
# Use a locked, explicit path for required code
require_dependency Rails.root.join('lib', 'vendor', 'daily_vendor_library')
# ... rest of processing
end
end