CVE-2025-61669: jupyter_server next parameter open redirect can redirect users to external domains

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-05-05 · updated 2026-10-07
Weakness: CWE-601

Description

Jupyter Server is the backend for Jupyter web applications. In jupyter_server versions through 2.17.0, the next query parameter in the login flow is insufficiently validated in `LoginFormHandler._redirect_safe()`, which allows redirects to arbitrary external domains via values such as `///example.com`. An attacker can use a crafted login URL to redirect users to a malicious site and facilitate phishing attacks. This issue is fixed in version 2.18.0.

Affected products

jupyter-server jupyter_server: before 2.18.0 — fixed in 2.18.0

How to fix

Upgrade to a fixed version: jupyter-server jupyter_server 2.18.0. Check the vendor advisory for mitigations.

References

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