JupyterHub has an Open Redirect Vulnerability

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

5.1 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-33709: 0.21% estimated exploitation activity in the next 30 days; percentile 11.81 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Affected Version JupyterHub <= 5.4.3 Impact An open redirect vulnerability in JupyterHub <=5.4.3 allows attackers to construct links which, when clicked, take users to the JupyterHub login page, after which they are sent to an arbitrary attacker-controlled site outside JupyterHub instead of a JupyterHub page, bypassing JupyterHub's check to prevent this. Patches Upgrade to JupyterHub 5.4.4 Workarounds A deployment can apply filters on the Location header in a reverse proxy such as nginx/apache/traefik.

Published by the source

3 Apr 2026, 21:36 UTC

Last modified by the source

13 Jul 2026, 07:26 UTC

Source last checked

26 Oct 2026, 13:40 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-3vff-hjqv-m7h8

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-3vff-hjqv-m7h8

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# Patch Next advisory brief: CVE-2026-33709

Advisory: JupyterHub has an Open Redirect Vulnerability
IDs: CVE-2026-33709, GHSA-3vff-hjqv-m7h8
Record: https://patchnext.com/advisories/cve-2026-33709 (revision 3, source checked 26 Oct 2026, 13:40 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: jupyterhub 5.4.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI jupyterhub: affected <= 5.4.3; fixed in 5.4.4

## Suggested inspection (read-only)
- `python -m pip show jupyterhub`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on jupyterhub.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-3vff-hjqv-m7h8 (OSV record GHSA-3vff-hjqv-m7h8 lists affected ranges: PyPI jupyterhub >=0 <5.4.4 (fixed))
- Verified: https://github.com/advisories/GHSA-3vff-hjqv-m7h8 (GitHub-reviewed advisory GHSA-3vff-hjqv-m7h8 lists affected ranges: PyPI jupyterhub >=0 <=5.4.3)

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