c3p0 is a JDBC Connection pooling library. In versions prior to 0.14.0,  c3p0 in combination with other libraries, can compose to a "sink" for  deserialization gadgets. The JDBC spec's DataSource.getConnection() and  ConnectionPoolDataSource.getPooledConnection() match the getXXX() form, so JavaBean libraries treat them as "properties" assumed safe while they actually call into JDBC drivers. Attackers can thus craft malicious  DataSource objects whose property lookups invoke vulnerable drivers, then  smuggle them in serialized form to where an application deserializes and auto-resolves bean properties — triggering the attack. This requires a  susceptible DataSource/ConnectionPoolDataSource and JDBC driver on the  CLASSPATH, plus a carrier that auto-looks-up JavaBean properties on = deserialization, most commonly a collection paired with an Apache commons-beanutils Comparator that sorts by bean properties. c3p0 supplied that susceptible DataSource/ConnectionPoolDataSource, which was an  essential component of the trigger. This issue has been fixed in version 0.14.0.