Information disclosure in Jupyter-Server Jupyter Server
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.
CVSS v3 metric
CVSS v3 base score 7.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H.
Affected products
- Jupyter-server Jupyter_server — versions < 2.21.0
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM)
- security-advisories@github.com (x_refsource_MISC)
- security-advisories@github.com (x_refsource_MISC)
- security-advisories@github.com (x_refsource_MISC)
Frequently asked questions
- What is CVE-2026-86049?
- CVE-2026-86049 is a high-severity vulnerability in Jupyter-Server Jupyter Server, classified under Insertion of Sensitive Information into Log File. CVSS score: 7.1/10. Published 2026-09-17.
- How severe is CVE-2026-86049?
- High severity. CVSS v3 base score is 7.1 out of 10.