Summary
The ?next=... URL query parameter has an open redirection vulnerability. In jupyter_server<=2.17.0, this URL query parameter allows redirection to arbitrary external domains, which can be exploited to facilitate phishing attacks on server users.
Details
The vulnerability is caused by insufficient validation in the LoginFormHandler._redirect_safe() method.
- Source code reference: https://github.com/jupyter-server/jupyter_server/blob/987ebdd5e188cdc49751b01a0d6782d686492a53/jupyter_server/auth/login.py#L33-L76
This vulnerability was originally reported by Noriaki Iwasaki. All discovery credit goes to them.
PoC
- Navigate to
http://localhost:8888/login?next=///google.com - Observe that the user is redirected to
google.comdespite it being an external domain.
The external domain passed in the ?next parameter may be replaced with a malicious lookalike to facilitate phishing attacks. Jupyter Server deployments served on a public domain are especially vulnerable, as prod.company.com may be redirected to a look-alike URL such as prod.company.dev.
Jupyter Server 2.18+
Workaround
None.
Impact
This vulnerability affects all users, especially enterprise users who work with sensitive/confidential data.
Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites. Typical impact: phishing and credential harvesting via a trusted domain.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2025-61669? CVE-2025-61669 is a medium-severity open redirect vulnerability in jupyter-server (pip), affecting versions <= 2.17.0. It is fixed in 2.18.0. Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites.
- Which versions of jupyter-server are affected by CVE-2025-61669? jupyter-server (pip) versions <= 2.17.0 is affected.
- Is there a fix for CVE-2025-61669? Yes. CVE-2025-61669 is fixed in 2.18.0. Upgrade to this version or later.
- Is CVE-2025-61669 exploitable, and should I be worried? Whether CVE-2025-61669 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-61669 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2025-61669? Upgrade
jupyter-serverto 2.18.0 or later.