CVE-2020-26275: 
Python vulnerability analysis and mitigation

The Jupyter Server, which provides backend services, APIs, and REST endpoints for Jupyter web applications like Jupyter notebook, JupyterLab, and Voila, was found to contain an open redirect vulnerability (CVE-2020-26275) before version 1.1.1. The vulnerability was discovered in December 2020 and could allow malicious actors to redirect users to untrusted websites (GitHub Advisory).

The vulnerability exists in the server's URL handling mechanism where a maliciously crafted link to a Jupyter server could redirect the browser to a different website. The issue particularly affects Jupyter servers running without a base_url prefix. A link to a Jupyter server may appear safe but could ultimately redirect to a spoofed server on the public internet. This vulnerability is similar to one that was previously patched in upstream notebook v5.7.8 (GitHub Advisory).

The vulnerability could be exploited to conduct phishing attacks by redirecting users from legitimate Jupyter server instances to malicious websites. While all Jupyter servers running without a base_url prefix are technically affected, the exploitation requires the attacker to know the Jupyter server hosts. This could lead to users unknowingly accessing malicious servers while believing they are interacting with legitimate Jupyter instances (GitHub Advisory).

The vulnerability can be exploited by crafting malicious links that appear to point to legitimate Jupyter server instances. However, the exploitability is limited to scenarios where the attacker knows the target Jupyter server hosts. The attack requires creating specially crafted URLs that can redirect users to malicious websites (GitHub Advisory).

The vulnerability has been patched in jupyter_server version 1.1.1. For users unable to upgrade, a workaround is available by running the server with a URL prefix using the command: 'jupyter server --ServerApp.base_url=/jupyter/' (GitHub Advisory).