Advisories for Pypi/Jupyterhub-Ltiauthenticator package

The LTI 1.1 validator stores OAuth nonces in a class-level dictionary that grows without bounds. Nonces are added before signature validation, so an attacker with knowledge of a valid consumer key can send repeated requests with unique nonces to gradually exhaust server memory, causing a denial of service.

Only users that has configured a JupyterHub installation to use the authenticator class LTI13Authenticator are influenced. LTI13Authenticator that was introduced in jupyterhub-ltiauthenticator 1.3.0 wasn't validating JWT signatures. This is believed to allow the LTI13Authenticator to authorize a forged request granting access to existing and new user identities.