Overview
CVE-2006-4111 describes a vulnerability in Ruby on Rails before 1.1.5 that allowed remote attackers to execute Ruby code with severe or serious impact via a File Upload request that manipulates the LOAD_PATH via an HTTP header. This is a CWE-94 style code injection risk stemming from untrusted input influencing code loading. In practice, an attacker could inject a header such as X-Load-Path that is prepended to the Ruby $LOAD_PATH, causing subsequent require or autoload calls to fetch attacker-controlled files. If those files contain malicious code, the server runs it with the app's privileges, potentially leading to full compromise.
The impact includes arbitrary code execution, which in turn can be leveraged to cause resource abuse, memory or CPU exhaustion, or complete service disruption. The root cause is trusting request headers to alter a global load path, enabling an attacker to influence which libraries the application loads. The recommended remediation is to upgrade to the patched Rails release (1.1.5 or later) and to stop using user-controlled load paths altogether; instead use explicit, whitelisted loading of libraries (e.g., via Bundler/gems) and avoid modifying $LOAD_PATH from request data.
This guide demonstrates a concrete remediation pattern: upgrade Rails to the fixed version and refactor code to prevent header-driven load-path changes, replacing dynamic, user-controlled requires with explicit, safe loading. It also discusses how to audit header handling and implement secure loading practices, referencing CVE-2006-4111 to anchor the guidance.
Affected Versions
Rails before 1.1.5
Code Fix Example
Ruby on Rails API Security Remediation
Vulnerable pattern:
class UploadsController < ApplicationController
def create
if (path = request.headers['X-Load-Path'])
# Dangerous: user-controlled input manipulating LOAD_PATH
$LOAD_PATH.unshift(path)
end
# This can load attacker-controlled code via a require below
require 'uploaded_library'
# ... use the loaded library
end
end
Fixed pattern:
class UploadsController < ApplicationController
def create
# Do not modify LOAD_PATH from user input
# Use a fixed, whitelisted loading strategy
safe_libraries = %w[uploaded_library safe_lib1 safe_lib2]
if params[:library] && safe_libraries.include?(params[:library])
require params[:library]
else
render plain: 'Forbidden', status: :forbidden
return
end
# ... use the loaded library
end
end