An issue was discovered in the Extended Choice Parameter (aka extended-choice-parameter) plugin 0.64 for Jenkins 2.89.3. The PATH_INFO filename is vulnerable to path traversal attacks via ..\ sequences to the /plugin/extended-choice-parameter/js/ URI.
Jenkins before 2.107 and Jenkins LTS before 2.89.4 did not properly prevent specifying relative paths that escape a base directory for URLs accessing plugin resource files. This allowed users with Overall/Read permission to download files from the Jenkins master they should not have access to. On Windows, any file accessible to the Jenkins master process could be downloaded. On other operating systems, any file within the Jenkins home directory accessible to the Jenkins master process could be downloaded.