The vulnerability stems from unencrypted credential storage in JabberBuilder.xml. Jenkins plugins typically handle configuration through Descriptor classes and XStream serialization. The saveConfiguration method (or equivalent persistence mechanism) would be directly writing credentials to disk without encryption. The DescriptorImpl.configure method would process form submissions containing credentials but fail to use Jenkins' credential encryption APIs. Confidence is high for the persistence mechanism due to the specific file path in advisories, and medium for the descriptor method due to typical Jenkins plugin patterns without seeing actual code.