# CVE-2026-35397: jupyter-server: Jupyter Server is the backend for Jupyter web applications

CVE-2026-35397 is fixed in jupyter-server on 1 platform by DEBIAN-CVE-2026-35397 (version 2.20.0-1), released May 5, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-35397
- Priority: High
- CVSS: 8.8 (high)
- EPSS: 0.0062
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 5, 2026

## Description

Jupyter Server is the backend for Jupyter web applications. In versions 2.17.0 and earlier, a path traversal vulnerability in the REST API allows an authenticated user to escape the configured root_dir and access sibling directories whose names begin with the same prefix as the root_dir. For example, with a root_dir named "test", the API permits access to a sibling directory named "testtest" through a crafted request to the /api/contents endpoint using encoded path components. An attacker can read, write, and delete files in affected sibling directories. Multi-tenant deployments using predictable naming schemes are particularly at risk, as a user with a directory named "user1" could access directories for user10 through user19 and beyond. A user who can choose a single-character folder name could gain access to a significant number of sibling directories.   Version 2.18.0 contains a fix. As a workaround, ensure folder names do not share a common prefix with any sibling directory.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | jupyter-server Debian 14 | 2.20.0-1 | [DEBIAN-CVE-2026-35397](https://patchblox.com/security/data/fix/linux/debian-cve-2026-35397.md) | May 5, 2026 |

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Data as of 2026-11-08T00:53:09Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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