In jupyterhub-kubespawner before 0.12, certain usernames will be able to craft particular server names which will grant them access to the default server of other users who have matching usernames.
CVSS 3.1HIGH 8.1·Network·Low privileges·No interaction·EPSS 0.01114·Published 2020-07-17·Fixed in 0.12, 0.12.0CWE-863