Repository Connector Plugin stores credentials in its global configuration file org.jvnet.hudson.plugins.repositoryconnector.RepositoryConfiguration.xml on the Jenkins controller as part of its configuration.
While the credentials are stored encrypted on disk, they are transmitted in plain text as part of the configuration form by Repository Connector Plugin 1.2.6 and earlier. This can result in exposure of the credential through browser extensions, cross-site scripting vulnerabilities, and similar situations.