In rare cases Jenkins Plain Credentials Plugin 182.v468b_97b_9dcb_8 and earlier stores secret file credentials unencrypted (only Base64 encoded) on the Jenkins controller file system, where they can be viewed by users with access to the Jenkins controller file system (global credentials) or with Item/Extended Read permission (folder-scoped credentials).
https://www.jenkins.io/security/advisory/2024-06-26/#SECURITY-2495