Jupyter Server versions 2.0.0 through 2.6.0 allowed a GatewayClient.url configuration to replace the normal kernel websocket handler with a channel handler that authenticated the user but omitted a required authorization check for kernel execution. This is a credential or privilege escalation vulnerability that enables an authenticated but restricted user to open an upstream kernel channel and run code as the kernel, exposing data, credentials, and permitting environment modification.

The vulnerability affects the Jupyter Server product from the jupyter‑server vendor. All releases between 2.0.0 and 2.6.0 are impacted. Any deployment that manually registers the deprecated jupyter_server.gateway.handlers module after 2.6.0 remains at risk, because the handler still bypasses kernel‑execute authorization.

The CVSS score of 8.8 indicates a high severity. The EPSS score of < 1% indicates a very low but non‑zero likelihood of exploitation, and the vulnerability is not listed in the CISA KEV catalog. Based on the description, it is inferred that the likely attack vector is network‑based via the GatewayClient WebSocket channel, which can bypass authorization once the user is authenticated. An attacker can execute arbitrary code on the kernel, potentially compromising data and system integrity.