CVE-2026-35397 jupyter-server path traversal allows access to sibling directories sharing root_dir name prefix
Authenticated users can escape the configured root directory to read, write, and delete files in sibling directories sharing a name prefix.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-35397?
CVE-2026-35397 is a high-severity path traversal vulnerability in jupyter-server jupyter_server, published on 5 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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.
Weakness: CWE-22
Which versions are affected by CVE-2026-35397?
3 open source packages ship an affected version, including jupyter-server. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
jupyter-server PyPI | All versions | 2.18.0 |
jupyter-server PyPI | All versions | 2.18.0 |
jupyter-server PyPI | All versions | 2.18.0 |
Products include Jupyter Jupyter Server.
How do I fix CVE-2026-35397?
Upgrade jupyter-server to 2.18.0 or later.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-35397 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-35397 exists.
Public exploit code: 1 proofs of concept on GitHub.
Other vulnerabilities in jupyter-server jupyter_server
- CVE-2026-44727 Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP
- CVE-2026-40110 jupyter-server CORS origin validation bypass via unanchored regex in allow_origin_pat
- CVE-2026-40934 jupyter-server authentication cookies remain valid after password reset due to static cookie secret
- CVE-2024-35178 Jupyter server on Windows discloses Windows user password hash
- CVE-2022-24757 Sensitive Auth & Cookie data stored in Jupyter server logs
Sources
Also known as CLEANSTART-2026-BF97060, CLEANSTART-2026-UA81846, DEBIAN-CVE-2026-35397, GHSA-5789-5fc7-67v3, PYSEC-2026-68, UBUNTU-CVE-2026-35397.