Comment Not a vulnerability in Java Commons Library (Score 5, Informative) 115
The linked article takes a lot of words to get to the point, which is that "WebLogic, WebSphere, JBoss, Jenkins, and OpenMMS, and many other pieces of software." will deserialize arbitrary user-supplied Java objects. To exploit that, you just provide a serialized class from commons-collections which (by design) executes the class's code during its deserialization process.
If your application doesn't whitelist the classes it deserializes from an untrusted user, you deserve everything you get.