GHSA-rrqh-93c8-j966

Summary

A denial-of-service vulnerability exists in ruby-saml even with the messagemaxbytesize setting configured. The vulnerability occurs because the SAML response is validated for Base64 format prior to checking the message size, leading to potential resource exhaustion.

Details

ruby-saml includes a message_max_bytesize setting intended to prevent DOS attacks and decompression bombs. However, this protection is ineffective in some cases due to the order of operations in the code:

https://github.com/SAML-Toolkits/ruby-saml/blob/fbbedc978300deb9355a8e505849666974ef2e67/lib/onelogin/ruby-saml/saml_message.rb

      def decode_raw_saml(saml, settings = nil)
        return saml unless base64_encoded?(saml) # <--- Issue here. Should be moved after next code block.

        settings = OneLogin::RubySaml::Settings.new if settings.nil?
        if saml.bytesize > settings.message_max_bytesize
          raise ValidationError.new("Encoded SAML Message exceeds " + settings.message_max_bytesize.to_s + " bytes, so was rejected")
        end

        decoded = decode(saml)
        ...
      end

The vulnerability is in the execution order. Prior to checking bytesize the base64_encoded? function performs regex matching on the entire input string:

!!string.gsub(/[\r\n]|\\r|\\n|\s/, "").match(BASE64_FORMAT)

Impact

What kind of vulnerability is it? Who is impacted?

When successfully exploited, this vulnerability can lead to:

• Excessive memory consumption
• High CPU utilization
• Application slowdown or unresponsiveness
• Complete application crash in severe cases
• Potential denial of service for legitimate users

All applications using ruby-saml with SAML configured and enabled are vulnerable.

Potential Solution

Reorder the validation steps to ensure max bytesize is checked first

def decode_raw_saml(saml, settings = nil)
  settings = OneLogin::RubySaml::Settings.new if settings.nil?

  if saml.bytesize > settings.message_max_bytesize
    raise ValidationError.new("Encoded SAML Message exceeds " + settings.message_max_bytesize.to_s + " bytes, so was rejected")
  end

  return saml unless base64_encoded?(saml)
  decoded = decode(saml)
  ...
end