What is CVE-2026-33709?

CVE-2026-33709 is a medium-severity vulnerability in Jupyter Jupyterhub, classified under URL Redirection to Untrusted Site (Open Redirect). CVSS score: 6.1/10. Published 2026-04-03.

How severe is CVE-2026-33709?

Medium severity. CVSS v3 base score is 6.1 out of 10.

Open Redirect in Jupyter Jupyterhub

CVE-2026-33709

JupyterHub is software that allows one to create a multi-user server for Jupyter notebooks. Prior to version 5.4.4, an open redirect vulnerability in JupyterHub 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. This issue has been patched in version 5.4.4.

Vulnerability class: Open Redirect

Published 2026-04-03 · last modified 2026-07-24.

CVSS v3 metric

CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.003 (21.7th percentile), scored 2026-10-18.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 22nd percentile — 21.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001

Affected products

Jupyter Jupyterhub
Jupyterhub — versions < 5.4.4

Weakness classification (CWE)

CWE-601 — URL Redirection to Untrusted Site (Open Redirect)

References

github.com/jupyterhub/jupyterhub/security/advisories/GHSA-3vff-hjqv-m7h8 (Mitigation, Vendor Advisory)
github.com/jupyterhub/jupyterhub/releases/tag/5.4.4 (Product)

Frequently asked questions

What is CVE-2026-33709?: CVE-2026-33709 is a medium-severity vulnerability in Jupyter Jupyterhub, classified under URL Redirection to Untrusted Site (Open Redirect). CVSS score: 6.1/10. Published 2026-04-03.
How severe is CVE-2026-33709?: Medium severity. CVSS v3 base score is 6.1 out of 10.