Summary
Jupyter Server: Gateway WebSocket handler bypasses kernel execute authorization
Jupyter Server's gateway WebSocket handler checks that a user is authenticated, but it does not ask the configured Authorizer whether that user may execute kernels.
In Jupyter Server 2.0.0 through 2.5.0, enabling GatewayClient.url automatically replaced the normal kernel channel handler with this gateway-specific handler. An authenticated user who is denied the execute action on the kernels resource can therefore still open a kernel channel and send messages to the upstream kernel.
Details
The normal handler performs the expected authorization check before creating the WebSocket connection:
The gateway handler only checks current_user and then opens the upstream channel. It never calls authorizer.is_authorized(...):
https://github.com/jupyter-server/jupyter_server/blob/v2.5.0/jupyter_server/gateway/handlers.py#L49-L75
https://github.com/jupyter-server/jupyter_server/blob/v2.5.0/jupyter_server/gateway/handlers.py#L87-L98
Gateway mode selected that handler automatically by replacing handlers with matching routes:
https://github.com/jupyter-server/jupyter_server/blob/v2.5.0/jupyter_server/serverapp.py#L437-L446
PR #1261 stopped replacing the normal handler and routed gateway traffic through GatewayWebSocketConnection instead. This appears to have fixed the default gateway configuration in 2.6.0, although the deprecated handler is still present in current releases and can still be registered directly.
https://github.com/jupyter-server/jupyter_server/pull/1261
Code-level validation
- Configure a custom Authorizer that returns false for
executeonkernelsfor a regular authenticated user. - Configure
GatewayClient.urlon Jupyter Server 2.0.0-2.5.0. - The normal
KernelWebsocketHandlerwould reject that user with 403 inpre_get. - Gateway mode replaces it with
WebSocketChannelsHandler. Itsauthenticatemethod only rejects anonymous users, andgetproceeds to the upstream gateway without an authorization decision.
Affected versions
- Default gateway configuration: 2.0.0 through 2.5.0
- 2.6.0 and later: the default path uses the authorized standard handler, but manually registering the deprecated
jupyter_server.gateway.handlersmodule still exposes the old behavior.
Impact
This is a missing authorization check, not an authentication bypass. It matters in deployments that use a restrictive custom Authorizer and Jupyter Gateway/Enterprise Gateway. A read-only or otherwise limited authenticated user can cross the intended authorization boundary and obtain kernel execution, with access to data and credentials available to that kernel.
The application does not perform an authorization check before performing a sensitive operation. Typical impact: unauthorized access to restricted functionality or data.
CVE-2026-114135 has a CVSS score of 8.8 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.6.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-114135? CVE-2026-114135 is a high-severity missing authorization vulnerability in jupyter-server (pip), affecting versions >= 2.0.0, < 2.6.0. It is fixed in 2.6.0. The application does not perform an authorization check before performing a sensitive operation.
- How severe is CVE-2026-114135? CVE-2026-114135 has a CVSS score of 8.8 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of jupyter-server are affected by CVE-2026-114135? jupyter-server (pip) versions >= 2.0.0, < 2.6.0 is affected.
- Is there a fix for CVE-2026-114135? Yes. CVE-2026-114135 is fixed in 2.6.0. Upgrade to this version or later.
- Is CVE-2026-114135 exploitable, and should I be worried? Whether CVE-2026-114135 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-114135 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-114135? Upgrade
jupyter-serverto 2.6.0 or later.