CVE-2020-26275 is a medium-severity (CVSS 6.1) Open Redirect vulnerability in jupyter-server. 1 public exploit reference exists, so weaponization risk is real. A fix is available for jupyter-server — see the affected versions and patch details below.
Jupyter Server open redirect vulnerability
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2020-26275 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
jupyter-serverReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Impact
What kind of vulnerability is it? Who is impacted?
Open redirect vulnerability - a maliciously crafted link to a jupyter server could redirect the browser to a different website.
All jupyter servers running without a base_url prefix are technically affected, however, these maliciously crafted links can only be reasonably made for known jupyter server hosts. A link to your jupyter server may appear safe, but ultimately redirect to a spoofed server on the public internet. This same vulnerability was patched in upstream notebook v5.7.8.
Patches
Has the problem been patched? What versions should users upgrade to?
Patched in jupyter_server 1.1.1. If upgrade is not available, a workaround can be to run your server on a url prefix:
jupyter server --ServerApp.base_url=/jupyter/
References
For more information
If you have any questions or comments about this advisory, or vulnerabilities to report, please email our security list [email protected].
Credit: Yaniv Nizry from CxSCA group at Checkmarx
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | jupyter-server | all versions | 1.1.1pip install --upgrade 'jupyter-server==1.1.1' |
Affected Products
jupyter serverjupyterResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for jupyter-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update jupyter-server to 1.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-26275 is resolved across your whole dependency graph.
Workarounds
Stop reflecting attacker-controlled destinations: resolve every redirect target against an allowlist of paths or hosts you own, prefer a server-side key over a full URL in the request, and reject absolute URLs entirely where the flow only ever needs a relative one.
Frequently Asked Questions
Is CVE-2020-26275 in your dependencies?
Find it across PyPI, including transitive dependencies.