MarkUs is a web application for the submission and grading of student assignments. Prior to version 2.9.4, MarkUs allows course instructors to upload YAML files to create/update various entities (e.g., assignment settings). These YAML files are parsed with aliases enabled. This issue has been patched in version 2.9.4.
https://github.com/MarkUsProject/Markus/security/advisories/GHSA-m9rx-85mx-q9h6