CVE-2026-33709: Jupyter JupyterHub open redirect vulnerability

CVE-2026-33709 · Severity: medium · CVSS 6.1 · Published 2026-04-03

JupyterHub, a platform used to manage multi-user Jupyter notebook environments, is vulnerable to an open redirect flaw. Attackers can create deceptive links that appear to lead to a legitimate JupyterHub login page but instead redirect the user to a malicious external website after they log in. This can be used in phishing campaigns to steal user credentials or deliver malware by exploiting the user's trust in the original domain.

Technologies: jupyterhub (PyPI). Vendors: PyPI.

Quick answers

Is CVE-2026-33709 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-33709 being exploited in the wild.
How severe is CVE-2026-33709?
Medium severity, with a CVSS score of 6.1, published 3 April 2026.
Which products and versions are affected?
jupyterhub (PyPI) <= 5.4.3, ECOSYSTEM:introduced=0,fixed=5.4.4.
Is there a fix for CVE-2026-33709?
Yes. jupyterhub (PyPI): upgrade to 5.4.4 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-33709 attacked?
It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-33709?
Check whether you run jupyterhub (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • jupyterhub (PyPI): upgrade to 5.4.4 or later
    pip install "jupyterhub>=5.4.4"

Technical details

An open redirect vulnerability (CWE-601) exists in JupyterHub versions prior to 5.4.4. The application fails to properly validate user-supplied redirect URLs, allowing an attacker to bypass internal checks designed to prevent redirection to external domains. An attacker can exploit this by crafting a URL that points to the JupyterHub login endpoint with a malicious destination in the redirect parameter. If a user clicks the link and authenticates, the application will redirect them to the attacker-controlled site. This issue is patched in version 5.4.4; as a workaround, administrators can implement Location header filtering at the reverse proxy level (e.g., Nginx or Apache).

Affected products

  • Jupyter JupyterHub < 5.4.4

Identifiers

  • CVE-2026-33709
  • GHSA-3vff-hjqv-m7h8
  • PYSEC-2026-2188

Timeline

  • 2026-03-26: other: Version 5.4.4 tagged on GitHub
  • 2026-04-02: advisory: GitHub Security Advisory published
  • 2026-04-03: disclosed: CVE published to NVD

References

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