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Response snapshot Oct 27, 2026, 04:06 UTC

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VulnerabilityCVE-2026-114135

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.

At a glance

Exploited
Not known
Severity
8.8 High (CVSS 3.1)
Chance of exploitation
0.5% in the next 30 days
Sources
2 independent sources

What to do

GitHub lists first patched versions: jupyter-server: 2.6.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-354v-3q48-cv69 (opens a new tab)

What happened

### Summary

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

Continue reading

The normal handler performs the expected authorization check before creating the WebSocket connection:

https://github.com/jupyter-server/jupyter_server/blob/v2.5.0/jupyter_server/services/kernels/websocket.py#L39-L47

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

1. Configure a custom Authorizer that returns false for `execute` on `kernels` for a regular authenticated user. 2. Configure `GatewayClient.url` on Jupyter Server 2.0.0-2.5.0. 3. The normal `KernelWebsocketHandler` would reject that user with 403 in `pre_get`. 4. Gateway mode replaces it with `WebSocketChannelsHandler`. Its `authenticate` method only rejects anonymous users, and `get` proceeds to the upstream gateway without an authorization decision.

### 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.

### 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.handlers` module still exposes the old behavior.

Affected package ranges reported by GitHub: jupyter-server: >= 2.0.0, < 2.6.0

Scores and how they were measured

CVSS base severity

8.8

Version 3.1As of

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

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.5%

Scored Percentile 41.4%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-354v-3q48-cv69 (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-354v-3q48-cv69, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-354v-3q48-cv69, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  4. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-354v-3q48-cv69, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  5. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-354v-3q48-cv69, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  6. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-354v-3q48-cv69, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  7. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-354v-3q48-cv69, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  8. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-354v-3q48-cv69, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  9. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-354v-3q48-cv69, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  10. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-354v-3q48-cv69, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  11. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-354v-3q48-cv69, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  12. Primary source

    NVD CVE-2026-114135 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  13. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  14. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-114135, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 22). Jupyter Server: Gateway WebSocket handler bypasses kernel execute authorization (CVE-2026-114135). https://kevwire.com/record/CVE-2026-114135

MLA

"Jupyter Server: Gateway WebSocket handler bypasses kernel execute authorization (CVE-2026-114135)." KEVWire, 22 Oct. 2026, kevwire.com/record/CVE-2026-114135.

Chicago

KEVWire. "Jupyter Server: Gateway WebSocket handler bypasses kernel execute authorization (CVE-2026-114135)." Last modified October 22, 2026. https://kevwire.com/record/CVE-2026-114135.

Evidence summary (plain text)

Jupyter Server: Gateway WebSocket handler bypasses kernel execute authorization (Oct 22, 2026).
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.
CVSS 8.8 (version 3.1; evidence as of Oct 22, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-114135).
EPSS 0.5% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-114135&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-354v-3q48-cv69: https://github.com/advisories/GHSA-354v-3q48-cv69
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQxNTo1Mjo1NlrOAAfxiA%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0OToxMlrOAAf0LQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NzoxN1rOAAf0Kg%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NTozNlrOAAf0Jw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NTowNVrOAAf0JQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0Mzo0NVrOAAf0Iw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0MzozMVrOAAf0Ig%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODozNTowMVrOAAZRcw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODozMDoyN1rOAAY_5Q%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODoyOTowNVrOAAfz8g%3D%3D
NVD CVE-2026-114135: https://nvd.nist.gov/vuln/detail/CVE-2026-114135
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?pubStartDate=2026-10-12T13:35:55.142Z&pubEndDate=2026-10-26T13:35:55.142Z&resultsPerPage=500&startIndex=8000
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-114135&date=2026-10-26
Record ID: CVE-2026-114135.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 01:40 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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