CVE-2026-86049
Jupyter Server is the backend for Jupyter web applications. Prior to version 2.21.0, the 5xx request logging path in jupyter_server/log.py copies the Referer header into a JSON header block without applying the token scrubbing used for the request URI. A request that returns HTTP 500 while the Referer contains a token-bearing URL can therefore write that token to server logs in plaintext. An attacker who can read those logs can recover the token and use the affected user's Jupyter Server permissions. This issue is fixed in version 2.21.0.
What this means for your business
- An attacker can use it remotely, over a network, with an ordinary user login, but only after tricking someone into an action such as opening a file or a link.
What to do
- 1Ask your IT team or provider whether any of your systems use the affected product.
- 2If you do, follow the vendor's guidance. No patch reference has been published yet.
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Scoring
- CVSS
- 7.1 (v3.1)
- Vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H- Weakness
- CWE-532
- Assigned by
- security-advisories@github.com
Dates
- Published
- 2026-09-17
- Last modified
- 2026-09-18
- Sources
- NVD
References
- https://github.com/jupyter-server/jupyter_server/commit/52513529af7096e622c00911b17627b266294717
- https://github.com/jupyter-server/jupyter_server/pull/1681
- https://github.com/jupyter-server/jupyter_server/releases/tag/v2.21.0
- https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-c3mw-737p-c7g2