Jupyter Server: Gateway WebSocket handler bypasses kernel execute authorization

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Jupyter Server is the backend for Jupyter web applications. From 2.0.0 until 2.6.0, enabling GatewayClient.url replaced the normal KernelWebsocketHandler with WebSocketChannelsHandler, which authenticated the user but did not call authorizer.is_authorized(...) for the execute action on the kernels resource. A restricted authenticated user could therefore open an upstream kernel channel and obtain kernel execution despite the configured Authorizer denying that action, exposing data and credentials available to the kernel and permitting modification or disruption of the kernel environment. The default gateway configuration is fixed in version 2.6.0. In 2.6.0 and later, the same authorization bypass remains possible when a deployment manually registers the deprecated jupyter_server.gateway.handlers module, because its handler still omits the configured kernel-execute authorization decision.

Source published

21 Oct 2026 19:58:51 UTC

Source modified

28 Oct 2026 01:36:08 UTC

Observed here

28 Oct 2026 02:51:34 UTC

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CVSS 3.1 · 8.8 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H