CVE-2026-114135: Jupyter Server: Gateway WebSocket handler bypasses kernel execute authorization
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.isauthorized(...) 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 jupyterserver.gateway.handlers module, because its handler still omits the configured kernel-execute authorization decision.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Jupyter Serverto a version that resolves this vulnerability.Fixed in 2.6.0
Event History
Frequently Asked Questions
Which deployments are exposed?
Deployments running Jupyter Server from 2.0.0 through 2.6.0 are exposed when GatewayClient.url is enabled. In 2.6.0 and later, exposure can still occur if the deployment manually registers the deprecated jupyter_server.gateway.handlers module.
What access does an attacker need?
An attacker needs an authenticated account that is restricted by the configured Authorizer from executing actions on kernels. No user interaction is required; the attacker can open an upstream kernel channel and bypass that kernel-execute authorization decision.
What is the impact of successful exploitation?
The attacker can obtain kernel execution despite the configured authorization restriction. This can expose data and credentials available to the kernel and allow modification or disruption of the kernel environment.
What should be checked during triage or used as a temporary mitigation?
Check whether GatewayClient.url is enabled and whether the deprecated jupyter_server.gateway.handlers module is manually registered. If patching is not immediately possible, disable the affected gateway configuration and avoid registering the deprecated handler module.