Invicti identified a Remote Code Evaluation (RoR - JSON) by capturing a DNS A request, which occurs when input data is run as code.

The JSON Parsing code in Rails 2.3 and 3.0 support multiple parsing backends. One of the backends involves transforming the JSON into YAML, and passing that through the YAML parser. Using a specially crafted payload, attackers can trick the backend into decoding a subset of YAML.

An attacker can execute arbitrary Ruby on Rails (RoR) code on the system. The attacker may also be able to execute arbitrary system commands.

Upgrade to version 2.3.16, 3.0.20, or higher, to address this vulnerability. If you are unable to upgrade, or apply the patches, you can work around this vulnerability by switching backends to the JSONGem backend. Place this code in an application initializer:ActiveSupport::JSON.backend = "JSONGem"