Jupyter Server has an open redirection vulnerability in `next` query parameter
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.
Impact
This vulnerability affects all users, especially enterprise users who work with sensitive/confidential data.
Patches
Jupyter Server 2.18+
Workaround
None.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | jupyter-server | < 2.18.0 | 2.18.0 |
References
- CVSS vector
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:H/SI:N/SA:N- Weakness (CWE)
CWE-601- Platform
- Python (PyPI)
- Package
jupyter-server- Disclosed
- 05.05.2026
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-67 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-qh7q-6qm3-653w - CC BY 4.0
Vulnerability history: jupyter-server
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 14
- First → latest
- 11.2020 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- High 7
- Medium 6
Disclosures per year
- 2020: 2
- 2021: 0
- 2022: 2
- 2023: 3
- 2024: 1
- 2025: 0
- 2026: 6
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Jupyter Server has an open redirection vulnerability in `next` query parameter this entry
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